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Technology Difficulties and Countermeasures of Automatic Vertical Drilling for Ultra-Deep Wells in Bozi Block of Tarim Basin
TENG Xueqing, LIU Hongtao, LI Ning, WANG Tianbo, RU Dajun, DONG Ren
 doi: 10.11911/syztjs.2020113
[Abstract](0) [FullText HTML](0) [PDF 640KB](0)
Abstract:
Bozi Block in Tarim Basin belongs to typical high dip angle, which has a large dip angle, strong natural deviation making ability, It is difficult to ensure well deviation control by using conventional deviation prevention and straight drilling technology. This paper analyzes the application difficulties of automatic vertical drilling technology in ultra deep wells of Bozi Block. In view of the strong downhole vibration and the difficulty of deviation control and straight drilling in the upper conglomerate formation of Bozi Block, the anti deviation drilling technology research is carried out in the aspects of shock absorption optimization, ultra deep well signal transmission, deviation prevention and straightening technology optimization. During the first opening of 198–417 m and 565–1 000 m sections of Well BZ1501, the average penetration time is 189 h, the average ROP is 2.43 m/h, and the well deviation is 0.2°. Compared with the conventional pendulum drilling tool and the vertical drilling system of Well BZ18, it has the advantages of long working life, fast ROP and well deviation control. Field application shows that the technology of deviation prevention and straight drilling has achieved good application effect for ultra deep wells in Bozi Block of Tarim Basin.
Oil-Based Drilling Fluid Technology for Deep Wells in West Region, Sichuan Basin
WANG Xingyuan, LU Dengyun, YUAN Zhiping
 doi: 10.11911/syztjs.2020116
[Abstract](1) [FullText HTML](1) [PDF 1378KB](0)
Abstract:
Deep formation collapse, well leakage accident occur frequently in West of Sichuan Basin. Thick filter cake is difficult formed in OBM and densification is low, which leads to strong wellbore pressure penetration. Aiming at above problems, according to drilling fluid film formation mechanism, a nanosized polymer emulsion was synthesized from styrene, acrylate and other materials using core-shell structure design to form a compact film with external adsorption. According to analysis of geologic, engineering characteristics of risky formations and Hands d90 fill rule, selecting "rigid, elastic, soft and fiber" to form the inner filling plugging agent. Film forming mechanism and morphology were studied by scanning electron microscope. Film-forming effect was evaluated by high temperature and high pressure filtration, water loss and oil loss. Through high temperature and high pressure sand bed filtration experiment, sealing capacity of filling material was evaluated. Experimental results show that nanometer polymer emulsion can form dense film in O/W emulsion and OBM, which can adsorbing on surface of mud cake effectively. Sealing ability of film is up to 2.0 MPa. Filling material added to OBM can increase bearing capacity of inner cake to ≥3.5 MPa. Above technology has been successfully applied in Shuangtan 6 well and Zhongjiang2 well, complex time of deep well leakage, collapse, stuck drilling and other accidents has been reduced to 3.41% and 0%.
Experimental Simulation of Effective Stress Changes in Underground Gas Storage during Injection and Production
YOU Lijun, SHAO Jiaxin, GAO Xinping, KANG Yili, WANG Furong
 doi: 10.11911/syztjs.2020102
[Abstract](0) [FullText HTML](0) [PDF 1363KB](0)
Abstract:
The change of effective stress in the periodic injection-production process of underground gas storage will cause stress sensitivity of the reservoir. Stress sensitivity test and stress sensitivity test considering effective stress action time were carried out, and the permeability of rock samples in the test process was tested. By means of scanning electron microscope (SEM), the fracture wall of rock samples before and after the test considering the effective stress action time was observed. The test results show that the stress sensitivity of carbonate fractures and matrix rocks is weak-moderately weak and none. The stress sensitivity of fracture and matrix rock samples with increased effective stress action time is moderately strong-strong and weak. Within 2 h, the permeability of fractured rock samples decreased by 5%–9%, and that of matrix rock samples decreased by 2%–3%. With the increase of effective stress action time, the fracture of micro-protrusions on rock fracture wall and the initiation and propagation of micro-fractures will strengthen the stress sensitivity of rock samples. The injection-production pressure of underground gas storage should be controlled reasonably, so as to weaken the stress sensitivity of underground gas storage.
The Technical Status and Development Recommendations for the Geothermal Energy Extraction Utilizing Abandoned Wells
SONG Xianzhi, XU Fuqiang, SONG Guofeng
 doi: 10.11911/syztjs.2020120
[Abstract](4) [FullText HTML](1) [PDF 943KB](1)
Abstract:
Geothermal energy is one of the renewable energy sources that replace fossil fuels, but the high development cost makes it difficult to promote and utilize. The petroleum industry produces a large number of abandoned wells every year. Using abandoned wells for geothermal development can alleviate energy problems, economize drilling costs and effectively control the pollution. Based on the current research status of geothermal development using abandoned wells, this work analyzes the feasibility of the abandoned wells transformation. This work elaborates the selection of the target wells and the utilization methods. This work also discusses the abandoned wells transformation and the heat extraction methods. On the whole, the geothermal energy extraction utilizing abandoned wells at home and abroad is still in the stage of theoretical research and experimental research, and there is still a big gap with industrial applications. Starting from the overall trend of geothermal energy extraction utilizing abandoned wells, this paper puts forward suggestions for the research direction: strengthening the research on multi-branch radial well technology, improving the heat extraction performance of abandoned well systems, establishing intelligent decision-making and optimization systems, and strengthening the research on ground supporting facilities. This paper has a certain guiding role in obtaining geothermal resources using abandoned wells.
Cementing Technology for Reservoir Protection in Parahuacu Oilfield, Ecuador
LI Wandong
 doi: 10.11911/syztjs.2020109
[Abstract](11) [FullText HTML](3) [PDF 973KB](3)
Abstract:
In reservoir cementing in Parahuacu Oilfield, Ecuador, edge-bottom-water channeling is prone to happen in the second interface, cement slurry filtrate and solid particles are easy to invade the reservoir pore throat, and conventional cement slurry is easy to leak to the reservoir. Through simulated flushing tests, the developments of acidic flushing fluid, temporary-plugging spacer fluid and interfacial cementation enhancer constituted a multi-effect pre-fluid system; through using hollow glass microsphere, setting up the liquid-solid ratio design window, controlling fluid loss and increasing the anti-water-channeling performance, developed an anti-water-channeling latex low-density cement slurry. Indoor test results show that the multi-effect pre-fluid system can remove 95.0% of the structural mud cake, make the permeability recovery value over 90.0% and increase cement interfacial bonding strength more than 5 times; the anti-water-channeling latex cement slurry has a density of 1.74 kg/L, its performance is stable, API water loss does not exceed 20 mL and static gel strength transition time is less than 10min. The research results were applied to 5 wells on site, with the design of centralizers installation and pump scheme, the casing centralization was up to 85.8%, the annulus displacement efficiency of cement slurry exceeded 95.0%, in the area of reservoir didn't exist the leakage of cement slurry and the channeling of edge-bottom-water, with a good cementing quality. It shows this cementing technology can meet the requirements of reservoir protection.
High-Performance Oil-Based Drilling Fluid Technology for Horizontal Wells in Madong Oilfield of Junggar Basin
ZHANG Xiong, YU Jin, MAO Jun, LIU Zulei
 doi: 10.11911/syztjs.2020106
[Abstract](57) [FullText HTML](11) [PDF 852KB](18)
Abstract:
There were technical difficulties such as drilling jamming, wellbore instability and low ROP caused by mudstone hydration, abnormal pressure and many gravel layers in the horizontal well deflection section and horizontal section of Madong Oilfield in Junggar Basin. In order to solve these problems, XZ high-performance oil-based drilling fluid technology research was carried out. According to the reservoir characteristics of the Madong glutenite oil field and the construction requirements of the mid-long horizontal sections, the formula of XZ high-performance oil-based drilling fluid was determined, and its performance of regulation of density、temperature resistance、shear force increase、sealing pressure、pollution resistance and frost resistance were evaluated. Experiments showed that the oil-based drilling fluid system has a wide density range, stable rheological properties and adjustable shear force between 1.35~2.01 g/cm3; its heat and freezing stability is good, and the low temperature can reach –24 ℃, the high temperature can reach 180 ℃; it has good emulsification stability, and the demulsification voltage is generally above 1000 V; it has strong anti-pollution ability, the concentration of anti-drilling cuttings pollution is equal or greater than 20%, the concentration of anti-formation water pollution is equal or greater than 20%, and the concentration of anti-cement pollution is equal or greater than 10%; its sealing ability is strong, when using sand discs with pore diameters of 120 μm and 150 μm for pressure sealing, the pressure bearing can reach 15 MPa. The oil-based drilling fluid system completed 4 well tests in the Lower Wuerhe Formation of the Madong Oilfield. The borehole stability is good, the well diameter enlargement rate of the inclined section is only 3.55%, and the trip is smooth. The average ROP is increased by 79% compared with the water-based drilling fluid system at the same horizon, and field applications have achieved excellent speed-up effects. The results prove that the use of XZ high-performance oil-based drilling fluid can solve the technical problems such as jamming, borehole instability, and low ROP in the development of Madong glutenite reservoirs, and meet the requirements of safe and fast drilling in the long horizontal section of Madong Oilfield.
Experimental and Numerical Study of Slotted Metal Pipes for Energy-Gathered Bundle Type Nesting Plugging
ZHANG Yiqun, YU Chao, CHENG Guangming, SONG Xianzhi, ZHAO Kexian
 doi: 10.11911/syztjs.2020107
[Abstract](48) [FullText HTML](10) [PDF 1236KB](11)
Abstract:
At present, there is still no solution to the karst lost formation encountered in the drilling and completion of oil, gas and geothermal resources. This paper presents the application of a novel technique, known as energy-gathered bundle type nesting plugging device, in fracture-cavity type carbonate reservoirs using both numerical simulation and experiments. Firstly, the composition and function of this new technique are presented. The invented device comprises external slotted metal pipes and an internal nesting explosion tool. Either spiral slits or straight slits are cut on the slotted metal pipe. Secondly, a coupled explosive-mechanical numerical model was established. The deformation of this device induced by explosion was simulated in order to analyze the performance of different kinds of slotted metal pipes and to optimize the bridging material and the slotting structure. Finally, an experimental setup was designed and several explosion experiments were conducted in air, submerged water, and submerged confining environments respectively. The numerical result shows that the series 5 aluminum alloy pipe with straight slotting patterns, exhibits a suitable tensile deformation without failure under the loading explosion of detonating cord, and can be utilized as the plugging tool. The experimental device can well simulate the downhole environment and verify the feasibility of the new plugging technology. The research results show that the energy-gathered bundle type nesting plugging technology is expected to better solve the technical problems that the plugging materials are difficult to retain and not easy to form the artificial well wall. Therefore, the success chance of plugging of cavity leakage can be improved and the cost of drilling and completion can be reduced.
Research and Application of Multi-Scale Fiber Toughness Cement Slurry Systems
ZOU Shuang, FENG Minghui, ZHANG Tianyi, ZOU Jianlong, ZENG Jianguo, ZHAO Baohui
 doi: 10.11911/syztjs.2020084
[Abstract](53) [FullText HTML](8) [PDF 902KB](20)
Abstract:
To solve the problems of high brittleness, low tensile strength, poor impact resistance and fracture resistance of the set cement in oil wells, three kinds of inorganic fibers with high tensile modulus, high tensile strength and good dispersibility were tested with the goal of optimizing them. This involved conducting orthogonal tests for the further developing a multi-scale fiber toughener BCE-230S. In addition, the effects of BCE-230S on the construction performance of cement slurry and the mechanical properties of set cement were investigated to determine the optimal dosage, by which a multi-scale fiber toughness cement slurry system was formed. The results showed that the splitting tensile strength, compressive strength and impact resistance of the set cement were significantly improved when compared with common cement. Young’s modulus was decreased significantly and the construction performance was ideal. The multi-scale fiber toughness cement slurry system has been applied to the low permeability fracturing wells in the Jidong Oilfield for more than 10 times in the well, and the cementing quality on the two cementing surfaces was measurably improved compared with that of adjacent wells. Later stage fracturing was successful, and no fluid channeling was observed during well testing. The results indicated that the multi-scale fiber toughness cement slurry system can effectively control the embrittlement of oil well set cement, so as to ensure the integrity of the wellbore and the long-term cementing quality, with potential for wide application.
The advance and development of proposals for leakage prevention and plugging technologies in Tarim Oilfield
WANG Tao, LIU Fengbao, LUO Wei, YAN Zhihang, LU Haiying, GUO Bin
 doi: 10.11911/syztjs.2020080
[Abstract](55) [FullText HTML](19) [PDF 580KB](25)
Abstract:
With the goal of solving the problem of circulation lost under complicated geological conditions of Tarim Oilfield, this paper analyzes the types of circulation lost in this oilfield and combines it with formation characteristics, and summarized the development history and achievements of leakage prevention and plugging technologies in this field. It shows that leakages induced by porosity, fracture and caverns are all encountered in Tarim Oilfield, but mainly caused by fractures and fracture-cavity. The development of leakage prevention and plugging technologies in this oilfield has gone through two stages: the establishment of basic system and the implementation of characteristic technology. A series of techniques have been formed such as oil-based drilling fluid leakage prevention and plugging, high-strength pressure-bearing plugging, high-pressure brine layer leakage prevention and plugging, and fracture-cavity leakage plugging. From the analysis and sorting, we have clarified current leakage prevention and plugging techniques in Tarim Oilfield and the remaining challenges in leakage control, and determined the trend of research. Based on the analysis, we proposed recommendations in those technologies for further development, such as strengthening formation prediction, developing or introducing new plugging technologies, enriching engineering techniques, and developing big data plugging software.
Research and test of volume fracturing technology for dry hot rock
CHEN Zuo, ZHANG Baoping, ZHOU Jian, LIU Honglei, ZHOU Linbo, WU Chunfang
 doi: 10.11911/syztjs.2020098
[Abstract](27) [FullText HTML](7) [PDF 1071KB](14)
Abstract:
The lithology, mechanical properties, and development and utilization methods of hot dry rock are quite different from conventional oil and gas resources. Shale oil and gas and tight sandstone oil gas fracturing technology cannot be replicated for hot dry rock, and appropriate fracturing technologies need to be re-studied. In this paper, using underground granite cores and large-size outcrop samples, high-temperature testing and true triaxial physical simulation system testing are used to analyze the mechanical properties of high-temperature rocks, and the morphological characteristics of crack initiation and propagation are simulated physically, and the brittle plasticity, rock failure characteristics, the characteristics of the influence of natural cracks on crack failure pressure, propagation path and shape. As a result, a low-displacement thermal fracturing + glue expansion joint + variable displacement cyclic injection volume fracturing technology was proposed, and experimental fracturing was carried out on site, which verified the results of laboratory research. Studies have shown that granite has strong plasticity, poor brittleness, and large horizontal stress difference at high temperatures. The rock is mainly damaged by tension and shear. Natural cracks and temperature difference effects can significantly reduce the fracture pressure and increase the complexity of the cracks. Dry hot rocks can achieve volume fracturing. The research results have a positive effect on promoting the development of hot dry rock thermal storage volume fracturing technology.
Exploration and Practice on One-trip Drilling Technology of Second Spud in Slim-hole in Southern Sulige Block
SHEN Zhaochao, HUO Rujun, YU Yanfei, DONG Yifan, NI Xiaowei, LEI Yu
 doi: 10.11911/syztjs.2020081
[Abstract](59) [FullText HTML](11) [PDF 692KB](23)
Abstract:
In order to further improve the drilling speed of slim hole wells in the Southern Sulige Block and reduce the development cost, one-trip drilling test in second spud was carried out in this area. By means of bit modification, the bit layout and streamline design are optimized to enhance the bit stability and abrasion resistance; the motor design is optimized to improve the service life and output power; the drilling parameters are optimized to implement the stimulated evolution drilling to improve rock breaking efficiency of the bit; the drilling assembly is optimized and the well trajectory is reasonably adjusted to ensure that one bit can drill both long stable section and down slope section. On this basis, one-trip test has been carried out on SN00XX platform twice, among which, well SN00XX-02 has realized one-trip of motors and well SN00XX-04 has realized one-trip of both motor and the bit. Then one-trip drilling technology was successfully applied in the other two wells. And the drilling cycle was shortened by about 8%. The results show that the one-trip technology can effectively achieve one-trip at second spud, with remarkable speed-up effect, which provides a new development direction for the follow-up drilling speed-up of slim-hole in Southern Sulige Block.
Design of Sponge Coring Tool with Graphen-Modified Lipophilic Sponge and Analysis of Oil Saturation
CHEN Zhongshuai, WU Zhonghua, SI Yinghui
 doi: 10.11911/syztjs.2020111
[Abstract](65) [FullText HTML](10) [PDF 879KB](7)
Abstract:
A new type of sponge coring tools is designed to accurately measure the oil saturation by gathering the crude oil released from the core. In the tools, graphen-modified sponge is used, and protected from pollution by protecting liquid and sealing piston. The sponge is produced by impregnating commercially available sponge in graphene sol, aging and supercritical drying. It has internal holes with varied size, and the capacity of oil absorption of sponge reaches 80.5 g/g. The clearance of sponge and core is determined as 0.6–1 mm by experiments, to meet requirements in oil absorption capacity and core entering liner barrel. In addition, method for analysis of oil saturation date is proposed. The new type of sponge coring tool could be widely used to efficiently gather oil released from the core and get a high core recovery rate.
Research and Application of Key Techniques for Sidetracking Horizontal Wells in Shallow Slimholes in Jidong Oilfield
LI Yunfeng, PAN Junying, ZHOU Yan, ZHU Kuanliang, WANG Zaiming
 doi: 10.11911/syztjs.2020090
[Abstract](85) [FullText HTML](10) [PDF 869KB](21)
Abstract:
In view of the technical problems of high pumping pressure, slow mechanical drilling speed, poor oil-water layer isolation effect, and rapid water cut rise after the oil well is put into production, the horizontal wells with ϕ139.7 mm casing window and sidetracking implemented in the early stage of Jidong Oilfield have been implemented. Research on the optimization of low-pressure-consuming drill pipes, the development and trial of small-size hydraulic pressurized speed-up tools, the optimization of completion liner size and completion methods, and technical measures to improve cementing quality. According to the small clearance between the wellbore and the annulus, a non-standard drill pipe with an outer diameter of ϕ79.4 mm was selected to reduce the pump pressure during construction, and a small hydraulic pressurized speed-up tool was designed and developed to realize the drill bit adjustment. The flexible pressurization effectively increases the rate of penetration; in view of the characteristics of the slim hole and the requirements of the completion method, a non-standard casing of ϕ95.3 mm is selected to meet the needs of the completion method and post-operation construction; the integrated application increases.
Production effect evaluation of CT in Fuling shale gas field
LIU Yaowen, LI Mu
 doi: 10.1911/syztjs.2020089
[Abstract](48) [FullText HTML](5) [PDF 1081KB](24)
Abstract:
As a gas production string, CT is more and more widely used in Fuling shale gas field. The specifications of the string are mainly ϕ50.8 mm×4.45 mm and ϕ38.1 mm×3.68 mm. The production effect of CT in different gas wells is different. In order to further improve the application effect of CT in shale gas wells, based on the field application, the evaluation of the production effect of CT is carried out from three aspects of gas well fluid carrying effect, wellbore pressure loss and stable production capacity of gas wells, and the influence of the specification, depth and timing of CT on the production effect of coiled tubing is analyzed. The results show that the critical liquid carrying capacity can be effectively reduced by 38% by using ϕ50.8 mm×4.45 mm CT compared with ϕ60.3 mm×4.83 mm tubing. The larger the water gas ratio is, the more significant the influence of CT specification and running depth on wellbore pressure loss and gas well stable production time is. In the range of water gas ratio of 0~1.5 m3/104 m3, the earlier it is put into the ϕ50.8 mm×4.45 mm CT for production, the longer the stable production time of the gas well is, the higher the cumulative gas production in the production stage of the gas well is. CT is conducive to the continuous and stable production of shale gas wells with low water gas ratio, and plays a guiding role in the optimization of production string of other shale gas fields.
Integrated processing technology for fishing and redressing of large diameter downholecaving
QIN Chun, CHEN Xiaoyuan, CHENG Zhiyong
 doi: 10.11911/syztjs.2020088
[Abstract](45) [FullText HTML](11) [PDF 1865KB](19)
Abstract:
The fissured deep mudstone & fractured formation are prone to collapse during drilling, and the size of caving is large. At present, conventional methods such as "section plug" cleaning, redressing with cone bit & reverse circulation junk basket are time consuming to deal with the tight pull caused by large-diameter caving, which seriously affects the cost and benefit of the well. Based on the analysis of the reasons which lead to the difficulty & long time for treating large-diameter caving by conventional methods, an integrated tool for breaking, redressing and fishing was developed. According to the bottom hole conditions, different technologies & parameters of redressing & fishing were adopted for removing caving, forming an integrated treatment technology for large-diameter caving. The technology has been applied in two wells where the hole was blocked due to the collapse of the wellbore. The integrated operation of redressing & fishing is carried out onsite, and proved to be 100% success in dealing with cave-in of hard-brittle mudstone. The research results show that the integrated treatment technology has a good effect on the quick treatment of large-diameter caving of hard-brittle mudstone and can effectively reduce the time of treating downhole problems.
Design and Implementation of a Downhole Safety Monitoring System
ZHANG Zhiliang, WANG Wei, YI Ming, LIU Qiang
 doi: 10.11911/syztjs.2020094
[Abstract](99) [FullText HTML](16) [PDF 1111KB](20)
Abstract:
In order to solve the problems of frequent downhole safety accidents, low early-warning efficiency, lagging safety monitoring technology in China, a downhole safety monitoring system with independent intellectual property rights was designed and developed. This system directly measures near-bit mechanical parameters and engineering parameters, and transmits the measured parameters to the drilling risk analysis and assessment system in real time by using the drilling fluid pulse, by which the received data can be analyzed and calculated to determine the type of drilling risk and assess the risk level. Field tests confirmed that the downhole safety system is fully functional and has a stable performance. The accuracy rate of the risk assessment is higher than 95%, and some technical indexes have reached the level of similar monitoring system abroad. The research showed that the downhole safety monitoring system could reduce the drilling risk and drilling cost in deep complex formations. It could create great economic benefits for it has solved the problem of low early warning efficiency of downhole safety accidents.
Experimental Study on Evaluation Method of Fracturing Effect of Fracture-Cavity Carbonate Reservoir
LI Xinyong, GENG Yudi, LIU Zhiyuan, WANG Wenzhi, ZHOU Zhou
 doi: 10.11911/syztjs.2020074
[Abstract](34) [FullText HTML](10) [PDF 951KB](5)
Abstract:
Fracture-cavity carbonate reservoir fracture fracturing communication evaluation system is missing, which makes it difficult to quantify the effect of fracturing reconstruction. It is necessary to establish a fracturing evaluation method for the characteristics of fracture-cavity carbonate rich in natural karst caves and fractures. By carrying out the hydraulic fracturing physical model experiment of artificial fracture-cavity carbonate samples, based on the experimental results, the evaluation criteria that meet the fracture-cavity carbonate fracturing characteristics are proposed, and the concept of fracture-cavity communication coefficient is proposed. And the quantitative analysis of fracture-cavity communication coefficient is used to evaluate the effect of in-situ stress difference on fracture-cavity carbonate fracturing effect. The experimental results show that the SRV coefficient used to evaluate the fracturing effect cannot accurately evaluate the fracture-cavity carbonate fracturing effect, and the fracture-cavity communication coefficient can make an accurate evaluation of the fracturing effect for the rock conditions where such fractures and caves are developed. In addition, the fracture-cavity communication coefficient is used to evaluate the effect of horizontal in-situ stress difference on fracture-cavity carbonate rock fracturing effect, and the law of increasing in-situ stress difference is obtained, and the fracture-cavity communication coefficient decreases first and then increases. The results of the study show that the influencing factors of fracture-cavity carbonate reservoirs on the effect of fracturing reconstruction are different from conventional reservoirs; the fracture-cavity communication coefficient based on the fracture-cavity carbonate fracturing experiment evaluation system The communication of fracture propagation will be more targeted analysis, and the effect of fracture and cave carbonate reservoir fracturing reformation will be evaluated more effectively.
Key Drilling Technology of Slim Hole in the South Block of Sulige Gas Field
YANG Jing, TU Fuhong, HUO Rujun, TAO Ruidong, SHANG Zibo, GUO Liang
 doi: 10.11911/syztjs.2020082
[Abstract](119) [FullText HTML](20) [PDF 690KB](30)
Abstract:
The directional drilling of the second-spud directional well in the slim borehole in the Southern Sulige Block faces technical difficulties. Such as difficult bit selection, difficult control of the borehole trajectory, well logging blocking, lost circulation. For this reason, PDC bit optimizations,mud motor improvements, drilling tool combination optimization, borehole trajectory control, drilling fluid system optimization and mud loss control were carried out, and Research on key technologies has formed the key technology for small borehole drilling in the Southern Sulige Block. And it has been applied in more than 80 wells, 6 wells with drilling cycle less than 10 days. Optimized drilling assembly and mud motor may make two trip drilling, even one trip drilling possible; control the density, reduce the pressure loss, pre-added plugging material with the drilling to through the easy leakage layer and got a remarkable effect on leak protection and sealing; optimize mud properties to improve the success rate of electrical logging. The key technology of slim hole provides effective technical support for the safe and efficient drilling of small hole directional wells in the Southern Sulige Block.
Leak-Proof Cementing Technology in the Third Opening and Sealing Section of the Ultra-Deep Well in Shunbei Oil and Gas Field Area 1
YANG Hongqi, SUN Lianhuan, AO Zhuqing, SANG Laiyu, YANG Guangguo, GAO Yuan
 doi: 10.11911/syztjs.2020110
[Abstract](55) [FullText HTML](8) [PDF 858KB](14)
Abstract:
Aiming at the problems of low pressure bearing capacity, serious drilling loss, long cementing section and high leakage rate of Silurian formation encountered during the third spud in area 1 of Shunbei Oil and Gas Field, the reasons are analyzed from two aspects of geological factors and engineering factors based on the analysis, the high anti extrusion hollow glass bead is selected as the lightening agent, and the low-density cement slurry system is developed based on the principle of particle size distribution; the formation pressure bearing capacity is improved by adding fibers of different sizes into the isolation fluid; based on the accurate judgment of the extremely easy lost layer, the "forward injection reverse extrusion" anti leakage cementing technology suitable for the liner cementing of long sealing section in ultra deep wells is developed. Laboratory tests show that under 100 MPa liquid column pressure, the density increase of low-density cement slurry is less than 0.03 kg/L, and the compressive strength of cement stone is more than 15 MPa, which has good bearing capacity and high compressive strength; the sealing isolation fluid can increase the bearing capacity of formation by 1.5 MPa. Combining the "forward injection and reverse extrusion" cementing technology with low-density cement slurry and lost circulation isolation fluid, a matching technology for lost circulation cementing of ultra deep wells in block 1 of Shunbei Oil and Gas Field is formed. This technology has been applied in more than 10 wells in the third spud in Shunbei Oilfield. The annular space of the applied wells is all sealed by cement slurry, and there is no lost sealing section, which solves the problem of cementing leakage in this opening. The research and application results show that the matching technology of long sealing section can effectively solve the cementing technical problems of ultra deep low pressure and easily lost circulation wells in block 1 of Shunbei Oil and Gas Field and similar blocks.
Rheological Properties of High-Density Oil-Based Drilling Fluid Considering Wall Slip Effect
LI Wenzhe, ZHONG Chengxu, JIANG Xuemei, LI Zhengtao, CAO Shiping, WU Shuang
 doi: 10.11911/syztjs.2020085
[Abstract](67) [FullText HTML](12) [PDF 969KB](20)
Abstract:
The wall slip effect will seriously affect the accurate measurement of the rheological properties of high-density oil-based drilling fluids, which requires detection and correction. Based on the Tikhonov regularization method, a correction method for wall slip during the measurement of the rheology of high-density oil-based shrinkage fluids was established. Rheological experiments were carried out with original and modified cylinder measuring system of six-speed rotational viscometer, the rheological properties and slip characteristics of high-density water-based drilling fluid were analyzed. The rheological model was optimized and the corresponding rheological parameters were also calculated. The influence of wall slip effects on the rheological parameters were compared and analyzed. The calculation results show that, compared with the rheological parameters before correction, the yield point of the high-density oil-based drilling fluid in the deep shale gas well field after slip correction is smaller, while the fluidity index is larger and close to 1.00, which means the true rheological properties can be expressed by Bingham model. When the wall shear stress is greater than the critical shear stress, the slip velocity increases exponentially as the wall shear stress increases. Studies have shown that high-density oil-based injection fluids will have a slip effect during rheological measurement. The rheological model and the rheological parameters before and after slip correction are significantly different. The effect of the slip effect should be eliminated during rheological measurement.
The Development and Field Testing of a High-Temperature Deep-Layer Open Hole Packer for Acid Fracturing Completion in Deep Carbonate Reservoirs
LIU Yang
 doi: 10.11911/syztjs.2020044
[Abstract](210) [FullText HTML](108) [PDF 964KB](32)
Abstract:
Premature aging of packer rubber elements and damage-prone of packer skeletons during the open hole well completions have been a problem in the deep Ordovician reservoirs of Northern Tarim Basin. To solve this, the causes of failures have been analyzed, after which a flexible anchor slip structure was designed for the protection of steel skeleton and prevention of damage to the rubber element caused by the excessive deformation of steel skeleton under large expansion ratio and high pressure. While maintaining the excellent aging resistance of fluororubber, plasticizing modification technology was used to improve its plasticity and thermal stability, which would make it easier to be moulded through mold injection. For the fluid inlet channel of the setting mechanism, a ball-activated protective sliding sleeve was designed to avoid the settling and clogging of drilling fluid. The improved open hole packer had a temperature resistance of 180 ℃ and strong sealing capacity, which was suitable for long-term sealing of irregular open hole formations. When applying such improved open hole completion packer in 4 wells in the Halahatang Area of Northern Tarim Basin, the RIH was smooth, the setting sign was obvious, and there was no abnormal casing pressure during the large-scale acid fracturing and production process. Research results showed that the improved packer met the needs of the integration of completion, acid fracturing and production testing, solved problems of deep oil and gas development in Tarim Basin, and had a good value for popularization and application.
Research on drilling tool wear and anti-wear technical schemes in hot dry rock drilling
WANG Heng, WANG Lei, ZHANG Dongqing, ZHANG Jinshuang
 doi: 10.11911/syztjs.2020099
[Abstract](50) [FullText HTML](9) [PDF 1340KB](18)
Abstract:
In order to clarify the wear mechanism of drilling tool and put forward appropriate anti-wear technical measures to reduce the wear of drilling tool, the motion state of drill string in wellbore was analyzed and the contact relationship model between drill string and borehole wall was described and established aiming at the problem of drilling tool wear in hot dry rock drilling. The finite element analysis model of drill string dynamics was further established by using finite element method. Taking a typical drilling well in hot dry rock as an example, the contact state between drilling tool and borehole wall is analyzed by solving the dynamic model of drill string. In order to reduce the contact force between the drilling tool and the borehole wall, the influence law of bottom hole assembly(BHA) and drilling parameters on the dynamic characteristics of drilling tools is analyzed. The recommended anti-wear technical scheme of BHA and drilling parameters is given through optimizing the BHA and drilling parameters. The technical scheme has been tested and applied in the hot dry rock drilling field. The footage is 116 m and the centralizer is worn by only 3.0 mm obtaining a good anti-wear effect. It provides a kind of solution to the problem of drilling tool wear in hot dry rock drilling.
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2020, 48(5): 0-0.  
[Abstract](34) [PDF 16186KB](15)
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2020, 48(5): 1-2.  
[Abstract](38) [PDF 327KB](9)
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Development Trends and Prospects of Less-Water Hydraulic Fracturing Technology
JIANG Tingxue, ZUO Luo, HUANG Jing
2020, 48(5): 1-8.   doi: 10.11911/syztjs.2020119
[Abstract](64) [FullText HTML](6) [PDF 1028KB](27)
Abstract:
In view of the large water consumption in conventional hydraulic fracturing, the rare implementation for waterless fracturing to reach high sand liquid ratio, and the difficulty in forming complex fractures with foam fracturing, the concept of a less-water hydraulic fracturing technology was proposed. Making full use of the technical advantages of hydraulic fracturing, waterless fracturing and foam fracturing, less-water hydraulic fracturing can reduce the water consumption to the maximum on the basis of satisfying the fracture volume. This paper mainly introduces the key technologies of less-water hydraulic fracturing including the composite rock breaking technology of supercritical carbon dioxide and low-viscosity slick water, balanced extension control technology for multi-cluster fractures based on multiple factors, sand adding technology during the fracture creating and sand carrying process, and flowback and production life-circle management technology, etc. According to these technologies, key methods of less-water hydraulic fracturing were proposed, such as remarkable enhancement of the fracturing fluids’ facture creating efficiency, maximal improvement of the sand liquid ratio in the multi-scale hydraulic fractures and the application of micro-foam fracturing fluid, etc. The proposal of less-water hydraulic fracturing technology has strong theoretical value and significance in idea change of fracturing and development effect enhancement in China.
Key Technology for Drilling and Completion of Shale Gas Horizontal Wells with Ultra-Long Horizontal Sections in Changning Block
WANG Jianlong, FENG Guanxiong, LIU Xuesong, GUO Rui, GAO Xuesheng, HUO Yang
2020, 48(5): 9-14.   doi: 10.11911/syztjs.2020086
[Abstract](145) [FullText HTML](23) [PDF 1418KB](82)
Abstract:
In order to solve the technical difficulties such as low ROP, long drilling cycle and high downhole risks of shale gas horizontal wells with ultra-long horizontal section in the Changning Block, with theoretical analysis and software simulation calculations, the well trajectory was optimized, the proper drilling equipment and casing running methods were selected, and technical measures were taken to reduce downhole risks, such as introducing vibration reduction and acceleration, leak prevention and plugging. These technologies were developed to form a key technology for the safe and efficient drilling and completion of shale gas horizontal wells with ultra-long horizontal sections in Changning Block. The technology had been tested in 3 horizontal wells with ultra-long horizontal section in Changning Block, no downhole failure occurred during drilling and completion, while ROP was increased by 2.5% and drilling cycle was shortened by 16.9% compared with the offset wells. This showed that this technology could solve the challenges in drilling and completion of those shale gas horizontal wells with ultra-long horizontal section in Chang-ning Block, ensure the safe and efficient drilling and completion in Changning Block, and could be popularized in this block.
Progress and Development Recommendations for Optimized Fast Drilling Technology in Shale Gas Horizontal Wells in the Nanchuan Area
PENG Xing, ZHOU Yucang, LONG Zhiping, ZHANG Shukun
2020, 48(5): 15-20.   doi: 10.11911/syztjs.2020057
[Abstract](115) [FullText HTML](21) [PDF 748KB](43)
Abstract:
the Nanchuan Area is another shale gas deliverability construction area of Sinopec and it follows the phase I deliverability construction of the Fuling shale gas area. In order to further improve the ROP and drilling efficiency of shale gas horizontal wells in this area, and to take into consideration the mature experiences of the Fuling shale gas phase I project, this paper systematically summarizes the existing problems in drilling the shale gas horizontal wells in this area. An optimized fast drilling technology for shale gas horizontal wells in Nanchuan Area was designed based on the analysis and research on the optimization of casing program, customized high-efficiency bit, wellbore trajectory design, cementing and completion modes, and the multi-well pad construction mode with combined drilling rigs, etc., This drilling technology was applied in more than 30 wells in the South Pingqiao Block of Nanchuan, which shortened the average drilling cycle from 92.00 d to 79.67 d and increased the average encountering rate of high-quality reservoirs to more than 98%. Further, more than 60% of these wells achieved a footage of more than 1,000 m in one trip, proving that the drilling technology could greatly improve the ROP and efficiency. On this basis, taken together with the horizontal well drilling difficulties in the JY10 Well Block and the Dongsheng Block with complex structure, recommendations were made to provide technical support for the subsequent deliverability, construction and efficient drilling in the Nanchuan Area.
Key Drilling Technologies of Infill Wells in the Fuling Shale Gas Field
LIU Yanqian
2020, 48(5): 21-26.   doi: 10.11911/syztjs.2020039
[Abstract](101) [FullText HTML](15) [PDF 697KB](40)
Abstract:
Infill wells in the Fuling Shale Gas Field are mostly located in the shale gas fracturing area with dense well pattern, resulting in many drilling technical problems, such as complex and frequent overflows and leakages, difficulty in determining reasonable drilling fluid density window, borehole collapse and sticking caused by fracturing fluid intrusion, and high difficulty in designing borehole trajectory to avoid fracturing interference, etc. To solve the above problems, technical research has been carried out from the perspectives of establishing a formation pore pressure calculation model for fracture zones, reasonable drilling fluid density window design, anti-fracturing interference borehole trajectory design, leakage prevention and plugging, and the prevention and control of simultaneous overflow and leakage in infill wells, etc., forming the key drilling technology suitable for infill wells in the Jiaoshiba main block of Fuling. The key technology has been applied in 31 wells in the Fuling Shale Gas Field, with an average horizontal interval of 1 933.25 m, an average drilling cycle of 52.38 days, and an average ROP of 10.31 m/h. Compared with previous infill evaluation wells, the ROP was increased by 15.3%, and the drilling cycle was shortened by 10.7%. The key drilling technology for infill wells in the Fuling Shale Gas Field provided technical support for the phase II productivity construction of the Fuling Shale Gas Field, and also provided technical references for the development of other shale gas fields.
Optimized Fast Drilling Technology for Horizontal Wells in the Tight Gas Reservoirs in Sulige Gas Field
SHI Peiming, XUE Rangping, WANG Xuefeng, WANG Wanqing, SHI Chongdong, YANG Yong
2020, 48(5): 27-33.   doi: 10.11911/syztjs.2020083
[Abstract](150) [FullText HTML](24) [PDF 617KB](36)
Abstract:
Problems occur when drilling horizontal wells in the tight gas reservoirs in Sulige Gas Field. They include low ROP, contradiction between formation collapse and lost circulation, long drilling cycles, etc. By analyzing the formation drilling challenges, technical research of factory drilling of horizontal wells was conducted to determine the best path forward. The areas studied included drilling mode optimization, “high efficiency PDC bit + high-power PDM” aggressive drilling technology, mode optimization of wellbore trajectory control technology with different offsets and sectional optimization of strongly inhibitive low-density CQSP-4 anti-collapse drilling fluid system. After the study was completed, recommendations were made regarding forming a new optimized fast drilling technology for horizontal wells in the tight gas reservoirs in Sulige Gas Field. In 2019, this technology was applied in 56 wells in Sulige Gas Field, with an average ROP of 12.76 m/h, an average drilling cycle of 39.12 days, and a well construction period of 52.20 days. Compared with those in 2018, in 2019 the ROP increased by 23.16%, the drilling cycle was shortened by 23.71% and the well construction period was reduced by 16.02%. The research and application showed that the key technology for horizontal wells drilling in the tight gas reservoirs in Sulige Gas Field had a remarkable effect on drilling acceleration, which provided technical support and the basis for best practices for the efficient development of the tight gas reservoirs in Sulige Gas Field.
Drilling Rate Improvement Technology Adopted in Well HWY-116 of the HWY Block, Saudi Arabia
YIN Huibo, SUO Zhongwei, LI Bodong, TU Yulin
2020, 48(5): 34-38.   doi: 10.11911/syztjs.2020048
[Abstract](83) [FullText HTML](16) [PDF 701KB](32)
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In order to raise the ROP in hard and highly abrasive formation in the third spud vertical section of the HWY Block in Saudi Arabia, the rotary percussion drilling technology test with hydraulic jet impactor was carried out in the third spud section of Well HWY-116. According to the relationship between the performance parameters of hydraulic jet impactor and the drilling resistance parameters of rock, the BHA was optimized with the drilling design of Well HWY-116 combined. The PDC bit matched the hydraulic jet impactor was selected to optimize the rotary percussion drilling parameters. Based on these optimizations, a drilling rate improvement scheme was formed for rotary percussion drilling with a ϕ228.6 mm hydraulic jet impactor suitable for Well HWY-116. The ROP in the third spud section of Well HWY-116 was 9.40 m/h, which was 45.5% higher than that of the adjoining wells. The results demonstrated that the ROP in hard and highly abrasive formation in the HWY Block of Saudi Arabia could be improved by the rotary percussion drilling technology with hydraulic jet impactor.
Experimental Study on the Scale Effect Law of Shale Strength and Deformation under Different Loading Modes
LI Shuai, CHEN Junbin, ZHAO Qinlei
2020, 48(5): 39-48.   doi: 10.11911/syztjs.2020075
[Abstract](36) [FullText HTML](8) [PDF 2886KB](5)
Abstract:
In order to explore the influence of different loading modes on the scale effect on shale strength and deformation, 7 shale outcrops of the Yanchang Formation in the Ordos Basin were taken and made into different sized core samples for uniaxial, triaxial compression and Brazilian splitting tests. The scale effect law of shale strength and deformation were analyzed under different loading modes. The results show that there are obvious differences in the scale effect on shale strength and deformation when core height/diameter ratio is larger or less than 2 in the triaxial compression test, and end friction effect and heterogeneity will play a decisive role when the ratio is between 0.4 and 0.8. In uniaxial compression tests, the scale effect of shale strength and deformation is the most significant, followed by Brazilian splitting, and triaxial compression. In uniaxial and triaxial loading tests of shale, there is no effect of scale on the sectional deformation characteristics of stress-strain curve of rock sample while it is various and the scale effect law is complex in Brazilian splitting test. Surprisingly, no scale effect is observed in shale failure modes under three loading modes. Heterogeneity, anisotropy and end friction effect are the fundamental causes in different effects of scale on strength and deformation under different loading modes. The experimental results can provide guidance for the selection of reasonable loading mode, testing scale and determination of rock mechanical parameters.
High Performance Anti-Sloughing Water Based Drilling Fluid Technology for Well Manshen 1 in the Ordovician Sangtamu Formation
YU Deshui, XU Hong, WU Xiuzhen, CHEN Yingwei, XU Jinyong
2020, 48(5): 49-54.   doi: 10.11911/syztjs.2020070
[Abstract](86) [FullText HTML](17) [PDF 596KB](22)
Abstract:
The lithology of Ordovician Sangtamu Formation in Manshen 1 fault zone is composed of mudstone and marl with well developed fractures and high risk of wellbore collapse, which brings great challenges to safe drilling. When Well Manshen 1 was drilled to the depth of 7 392.54 m (Sangtamu Formation), a strike slip fault zone was encountered, resulting in well collapse and sticking of drill tools, which was difficult to deal with. Backfill sidetracking was thus implemented. To solve this, the formation characteristics of Sangtamu Formation were analyzed, and the high-performance anti-sloughing water based drilling fluid technology was developed. Reasonable drilling fluid density was selected to mechanically support the borehole wall, compound fluid loss control measures were adopted to reduce the damage caused by filtrate on the water sensitive mudstone formation, and multi-amino borehole wall inhibitors was introduced while increasing K+ content to achieve a multiple anti-sloughing effect. At the same time, the temperature resistance, lubrication property and plugging performance of drilling fluid were improved to meet the requirements of inhibition, plugging, anti-sloughing and high temperature stability of the Sangtamu Formation. The application in the sidetracked borehole of the Well Manshen 1 showed that the drilling fluid performance was stable during sidetracking, the K+ content was maintained to be at around 35 000 mg/L, and the high temperature and high pressure filtration rate was reduced from 11.3 mL to 8.0 mL at 150℃. During the whole construction, no borehole instability occurred in the Sangtamu Formation. The well was successfully drilled to the total depth of the third spud, and the casing was set in place in one run. This showed that the anti-sloughing effect of high performance water based drilling fluid was remarkable, and it achieved the expected goal.
Research and Field Tests of the Lubrication and Friction Reduction Technology of High Density Drilling Fluid in Horizontal Wells
ZHEN Jianwu
2020, 48(5): 55-60.   doi: 10.11911/syztjs.2020076
[Abstract](62) [FullText HTML](7) [PDF 1167KB](17)
Abstract:
Due to the poor lubricity and high friction during the drilling of horizontal wells by using high-density water-based drilling fluids, the lubrication and friction reduction technology was studied, and factors influencing the lubricity and friction reduction performance of high-density drilling fluids were analyzed. Subsequently, lubricant Rhj-1, a lubricant with long-chain fatty acid vegetable oil as the raw material, was developed. The performance evaluation results showed that the lubricant RHJ-1 could reduce the extreme pressure lubrication coefficient of 5.0% bentonite slurry to 0.040. The lubrication coefficient of drilling fluid with a density of 2.10 kg/L could be reduced to a minimum of 0.105 after adding lubricant RHJ-1, and its temperature resistance ability could reach 150 ℃. For the drilling fluids with cuttings powder dosages of 10.0% and 15.0%, when the dosage of lubricant RHJ-1 was increased to 4.0%, the maximum reduction rate of drilling fluid lubrication coefficient could reach 55.58%. In order to ensure the lubricity and friction reduction of high-density drilling fluids in drilling horizontal wells, technical measures such as controlling the solid content and making use of the "bearing" effect of weighting agent, etc. were taken, thereby forming the lubrication and friction reduction technology for high-density drilling fluids. This technology was tested in Well WY23-4HF located in the deep shale gas block in Southwest China, and the tripping out friction after drilling was only 300 kN, which fully met the requirements of lubrication and friction reduction in the drilling of horizontal section. The results showed that the high-density drilling fluid technology for lubrication and friction reduction for horizontal wells is feasible and effective, and is worthy for popularization and application.
Research on Stratum Settlement and Wellhead Stability in Deep Water during Hydrate Production Testing
LI Lilin, YANG Jin, LU Baoping, KE Ke, WANG Lei, CHEN Kejin
2020, 48(5): 61-68.   doi: 10.11911/syztjs.2020095
[Abstract](74) [FullText HTML](12) [PDF 1374KB](35)
Abstract:
During hydrate production testing in deep-water non-diagenetically altered formations, subsea stratum settlement may occur after the decomposition of gas hydrate in a large area of weakly consolidated formation accompanied by an increase of production test time, resulting in wellhead and subsea manifold damage as well as the failure of the production testing project. To solve this problem, an analytical model of subsea stratum settlement and wellhead stability in non-diagenetically altered formations during hydrate production testing was established. Negative friction and drop-down load produced by hydrate decomposition were considered to be the main factors leading to wellhead instability, and the finite element strength reduction method was used to simulate the influence of hydrate decomposition on stratum settlement and wellhead stability. The results showed that the negative friction resistance around the pipe string after hydrate decomposition was mainly distributed in the area about 1/3 the length of conductor above the bottom, and the larger the hydrate decomposition radius, the higher the hydrate saturation, and the greater the negative friction resistance. The laboratory simulation test was carried out to explore the influence of hydrate decomposition on wellhead stability by means of the self-developed wellhead simulation device for gas hydrate production. The results showed that the relative error between the test result and simulation result of negative friction resistance was less than 10%, which verified the reliability of the calculation model and numerical simulation results. The research results can provide a theoretical reference for the time control and wellhead safety assessment of hydrate production test in deep water non-diagenetic formations.
Development and Applications of a Compound Axial and Torsional Impact Drilling Tool
LIU Shubin, NI Hongjian, ZHANG Heng
2020, 48(5): 69-76.   doi: 10.11911/syztjs.2020072
[Abstract](140) [FullText HTML](18) [PDF 1542KB](57)
Abstract:
To improve the rock-breaking efficiency of PDC bits and reduce stick-slip vibration, a compound axial and torsional impact tool was developed. This tool, characterized by a simple structure and the synchronous action of axial and torsional impacts, is used to break rocks. To do so, it used a self-excited oscillation pulse jet as its energy source, and converted axial impact force into compound axial and torsional impacts through helical surface structure. Field applications showed that: compared with conventional drilling tools, the ROP of this compound axial and torsional impact tool was increased by 95.2%–193.8%, and the footage of a single bit was increased by 46.4%–229.2%. Compared with PDM drills, the ROP of this tool was increased by 71.0% while compared with axial impact tools, the ROP of this tool was increased by 66.3%, and the footage of a single bit was increased by 194.0%. Compared with torsional impact tools, the ROP of this tool was increased by 30.2%–46.8%, and the footage of a single bit was increased by 17.2%–191.8%. The research results showed that the developed compound axial and torsional impact tool can improve rock-breaking efficiency and reduce the stick-slip vibration in hard formations. With its remarkable rock-breaking effects and ROP improvement, this tool is worth of application and widespread implementation.
Key Technology of Volumetric Fracturing in Deep Shale Gas Horizontal Wells in Southern Sichuan
ZENG Bo, WANG Xinghao, HUANG Haoyong, ZHANG Nanqiao, YUE Wenhan, DENG Qi
2020, 48(5): 77-84.   doi: 10.11911/syztjs.2020073
[Abstract](99) [FullText HTML](14) [PDF 1088KB](46)
Abstract:
There are persistent problems of immature fracturing technology, unreasonable key parameters, and low production of single well after fracturing in deep shale gas horizontal wells in Southern Sichuan. This paper introduces a process for optimizing the fracturing process and key parameters based on laboratory evaluation and numerical simulation by combining the geological engineering characteristics of deep shale reservoirs in Southern Sichuan through comprehensive analysis of fracturing effect of fractured wells. It focuses on improving the complexity of fracture networks, increasing the volume of fracturing stimulation, and maintaining the long-term conductivity of fractures. The key technology of volumetric fracturing for deep shale gas horizontal wells that focuses on“dense stage+short cluster spacing, equal-holesize large hole perforation, sand fracturing with low viscosity slick water at high pumping rate, high strength proppant with small particle size combinations, and large-scale fracturing with high-strength”is formed. After the application of this technology in Well Z3, its production achieved the rate of 21.3×104m3/d, which doubled and even more than that of wells with normal fracturing methods in the same block. In addition, high-yield production was achieved in several gas wells by applying this technology in deep shale gas horizontal wells in Southern Sichuan. This demonstrated that the technology has good adaptability and can be widely used. The successful application of this key technology in Southern Sichuan has laid a foundation for effective development of shale gas resources with depth around 3 500–4 500 m in Southern Sichuan.
Research on the Microscopic Pore Producing Characteristics of Tight Reservoirs Displaced by Different Gas Injection Media
LI Erdang, HAN Zuowei, GAO Xiangrui, MA Mingyu, QIU Junchao
2020, 48(5): 85-91.   doi: 10.11911/syztjs.2020078
[Abstract](73) [FullText HTML](11) [PDF 975KB](10)
Abstract:
In order to provide clarity in the microscopic oil displacement mechanisms of tight reservoirs displaced by different gas injection media, core displacement experiments of N2 and CO2 injection were carried out respectively based on the principle of NMR T2 spectrum test. The microscopic displacement mechanisms of N2 immiscible flooding and CO2 miscible flooding were studied at the microscopic pore scale, and the oil production from pores with different pore sizes during displacement was evaluated. The results show that final recovery percent from N2 immiscible flooding and CO2 miscible flooding has little difference. The N2 flooding process can be divided into three stages: the non-breakthrough stage, the early breakthrough stage and the mid-late breakthrough stage. The recovery percent from small pores is higher than that from large pores. However, the oil recovery percent from large pores is greatly improved in CO2 miscible flooding, while it is relatively low from small pores. The distribution of microscopic pore structure is the main cause for the difference in recovery percent between large and small pores in the process of N2 and CO2 flooding. The results show that the development effect of N2 flooding in tight reservoirs is better than that of CO2 flooding, which provides a theoretical basis for the development of Chang 6 reservoir by N2 flooding in Ansai Oilfield .
An Experimental Study on the Plugging Mechanisms of Sand-Preventing Medium in the Near-Well Zone of Sand Control Wells in Heterogeneous Polymer-Flooding Reservoirs
WANG Lizhi, DONG Changyin, HE Haifeng, CAO Qingping, SONG Yajun
2020, 48(5): 92-99.   doi: 10.11911/syztjs.2020118
[Abstract](39) [FullText HTML](9) [PDF 1527KB](8)
Abstract:
In light of the plugging problem in oilfield development using the heterogeneous polymer flooding, a simulation experiment to evaluate the plugging due to polymer plug in the sand-preventing medium in the near-well zone was carried out. It used a experimental simulation device of medium plugging of heterogeneous composite flooding. In the experiment, formation sand with grain sized averaging a diameter of 0.15 mm and gravel with a diameter range of 0.6–1.2 mm were used. In conjunction, three types of fluids, including clear water, a tackifying base fluid and a compound fluid contained PPG and polymer material were used. Further, the polymer plug samples in the sand control wells were used, respectively. The results showed that while it was in the gravel packing layer, the plug tended to migrate along the high permeability zone. Carried by fluid shear, the small viscous balls would be peeled off from the plug and then squeezed into the pores and throats in the deep gravel layer. These small, viscous balls impeded the migration of formation sand and intensified the degree of plugging degree in the gravel layer, which was positively related to the plug content. The outcome was a decrease in overall permeability. The results showed that the plugging in the near-well zone of gravel packed sand control wells treated by heterogeneous polymer flooding was a result of physical and chemical compound plugging of polymer dope, plug and solid particles. Early de-plugging measures should be taken to prevent plugging degree aggravation.
Effect of Temperature on the Imbibition Efficiency of the Jimusar Tight Oil Reservoir
XU Feng, YAO Yuedong, WU Chengmei, XU Zhang, ZHANG Jinfeng, ZHAO Guoxiang
2020, 48(5): 100-104.   doi: 10.11911/syztjs.2020114
[Abstract](51) [FullText HTML](16) [PDF 761KB](14)
Abstract:
In order to specify the effect of temperature on the imbibition efficiency in tight reservoirs after dense cut volume fracturing, imbibition mechanism experiments on the natural tight oil reservoir cores of Lucaogou Formation of Jimusar Sag were carried out under different temperature and pressure conditions by using the HTHP imbibition experimental apparatus for tight cores. The experimental results of imbibition and oil displacement showed that the imbibition efficiency increases as the temperature increases, the imbibition rate also accelerates with the increasing temperature, and the time required for imbibition reaction is reduced. When the experimental temperature is higher than the in-situ tight oil reservoir temperature of Jimusar Sag, the temperature increase has a minor effect on the imbibition efficiency. Correspondingly, when the experimental temperature is lower than the reservoir temperature, the lower the temperature, the greater its influence on the imbibition efficiency. There is a positive correlation between the imbibition amount and the saturated oil mass per unit area at different temperature conditions. The results indicated that temperature change has a great effect on the imbibition and oil displacement of the Lucaogou tight oil reservoirs in the Jimusar Sag. Therefore, the cold damage to the formation caused by the fracture fluid should be controlled as much as possible in the volume fracturing of tight oil reservoirs.
Scaling Spot Prediction and Analysis of Influencing Factors for a Geothermal Well in Boye County, Hebei Province
LIANG Haijun, GUO Xiaofeng, GAO Tao, BU Xianbiao, LI Huashan, WANG Lingbao
2020, 48(5): 105-110.   doi: 10.11911/syztjs.2020096
[Abstract](76) [FullText HTML](11) [PDF 1314KB](12)
Abstract:
Calcium carbonate scaling in geothermal wells seriously hinders the sustainable development and utilization of geothermal energy. In order to provide a theoretical basis for the implementation of scale inhibition technology in geothermal wells, the scaling spots of a geothermal well in Boye County of Hebei Province were numerically simulated. Based on the casing program of geothermal wells, the influencing factors and scaling spot depth prediction were studied by using WELLSIM. The results showed that fluid temperature at the bottomhole calculated from the composition of outlet fluids was 128.0 ℃. The geothermal fluid pressure drops rapidly as it rose along the wellbore. A flash occurred at the depth of 56.10 m, the dryness and CO2 partial pressure sharply changed accordingly. The flash depth of geothermal fluids migrated downwards with the increase of CO2 mass fraction, NaCl mass fraction and geothermal fluid flow rate, in which CO2 mass fraction played the decisive role. In field scale prevention practice, the setting depth of the submersible pump and the injection depth of the scale inhibitor should be below the flash depth of 56.1 m. The research shows that the flash depth can be adjusted by controlling the wellhead pressure and flow rate to accomplish the collaborative optimization of geothermal exploitation and scale prevention.
A Study on the Logging-Based Identification Method for Reservoir Fluid Properties of the Yan’an Formation in the Huanxi–Pengyang
ZHANG Congxiu, HAO Jinmei, LIU Zhiheng, GUO Haopeng
2020, 48(5): 111-119.   doi: 10.11911/syztjs.2020079
[Abstract](72) [FullText HTML](21) [PDF 2454KB](14)
Abstract:
In view of the difficulty in identifying the reservoir fluid properties of the Yan’an Formation in the Huanxi–Pengyang Area, beginning with the conventional interpretation difficulties of logging and mud logging, the Fisher discrimination method in SPSS software was introduced, with the concept of Big Data, the logging/mud logging parameters were deeply mined. Considering the recognition rate and separation degree, 15 parameters of reservoir fluid sensitivity were selected to identify the classification of Fisher non-standardized discriminant function, and the accuracy of fluid identification could reach 92.8%. Functions F1 and F2 were selected for their large contribution rate and intersected to plot the interpretation chart, and the identification rate of the chart was 89%. The interpretation chart was applied in the fluids interpretation and evaluation of 10 layers in 9 wells of Huanxi–Pengyang Area with a coincidence rate of 80%, and no valuable layers were missed. The application results showed that the Fisher discriminant method is suitable for high accurate identification of reservoir fluid properties in similar reservoirs, and it is worthy of wide adoption.
Optimal Design of a Downhole Seismic Generator
FENG Jin, CHI Shaolin, ZHANG Manlai, CHEN Wei, HUANG Xinyu
2020, 48(5): 120-126.   doi: 10.11911/syztjs.2020117
[Abstract](52) [FullText HTML](10) [PDF 1641KB](6)
Abstract:
Aiming at the problem of low seismic intensity while drilling, which is detrimental to the anti-collision monitoring between boreholes, an energy storage downhole seismic generator was designed.This generator is composed primarily of a piston, spring, impact hammer, anvil and a delay device. It was able to achieve high efficiency impact by means of the energy storage of drilling fluid. In order to achieve the optimal performance, taking the impact hammer as research object, the impact hammer flow passage model of downhole seismic generator was established. With the CFD software, the influence law on the output performance parameters of downhole seismic generator brought by the spring stiffness, impact hammer mass, throttling area, the outlet diameter, quantity and drilling fluid density were analyzed based on the CFD dynamic grid technology. The results showed that the throttling area, number of outlets, outlet diameter and drilling fluid density were positively correlated with the output performance parameters of downhole seismic generator. The greater the spring stiffness, the smaller the displacement corresponding to the maximum impact energy of the impact hammer. Correspondingly, the greater the mass of the impact hammer, the lower the velocity. Based on the results of single factor analysis, and by taking the impact energy of impact hammer as the optimization target, the optimal combination of design parameters was obtained by the orthogonal test. The results indicated that each design parameter had its unique effect on the output performance of downhole seismic generator. While the outlet diameter and spring stiffness play a prominent role on the output performance of the generator, the throttling area, hammer mass and number of outlets have a significant role on it, and the influence of drilling fluid density is not significant.Thus, the optimal combination of design parameters was selected based on the research results, which can provide a basis for the design of downhole seismic generator.
Drilling Technology Challenges and Resolutions in Fuling Shale Gas Field
Niu Xinming
2014, 42(4): 1-6.   doi: 10.3969/j.issn.1001-0890.2014.04.001
[Abstract](5425) [PDF 1006KB](4007)
Large-Scale Multi-Stage Hydraulic Fracturing Technology for Shale Gas Horizontal Well JY1HF
Zhou Dehua, Jiao Fangzheng, Jia Changgui, Jiang Tingxue, Li Zhenxiang
2014, 42(1): 75-80.   doi: 10.3969/j.issn.1001-0890.2014.01.015
[Abstract](6022) [PDF 1149KB](4174)
The Key Drilling Technologies in Fuling Shale Gas Field
Ai Jun, Zhang Jincheng, Zang Yanbin, Xu Mingbiao
2014, 42(5): 9-15.   doi: 10.11911/syztjs.201405002
[Abstract](4107) [PDF 1084KB](4019)
Application of Multi-Well Pad in Unconventional Oil and Gas Development in China
Zhang Jincheng, Sun Lianzhong, Wang Jiachang, Zang Yanbin
2014, 42(1): 20-25.   doi: 10.3969/j.issn.1001-0890.2014.01.004
[Abstract](4592) [PDF 1211KB](4003)
Integration Technology of Geology Engineering for Shale Gas Development
Zeng Yijin
2014, 42(1): 1-6.   doi: 10.3969/j.issn.1001-0890.2014.01.001
[Abstract](4310) [PDF 1065KB](4473)
Status and Prospect of Multi-Well Pad Drilling Technology in Shale Gas
Chen Ping, Liu Yang, Ma Tianshou
2014, 42(3): 1-7.   doi: 10.3969/j.issn.1001-0890.2014.03.001
[Abstract](3882) [PDF 1031KB](3973)
A New Method for Evaluating Shale Fracability Index and Its Application
Jiang Tingxue, Bian Xiaobing, Su Yuan, Liu Shuanglian, Wei Ran
2014, 42(5): 16-20.   doi: 10.11911/syztjs.201405003
[Abstract](3704) [PDF 1055KB](3676)
Development and Pilot Test of Hydro-Oscillator
Li Bo
2014, 42(1): 111-113.   doi: 10.3969/j.issn.1001-0890.2014.01.022
[Abstract](3838) [PDF 1085KB](4069)
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