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.
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 Changning shale gas horizontal wells with ultra-long horizontal sections. 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 Changning Block, ensure the safe and efficient drilling and completion in Changning Block, and could be popularized in this block.
Aimed at the difficult identification of the fluid properties of Yan'an formation in Huanxi-Pengyang area, Fisher discriminant method is introduced during welllogging and mud logging conventional interpretation. Based on the concept of big data, the logging parameters of reservoir are deeply mined. Considering two aspects of recognition rate and separation degree, 15 sensitive parameters on the reservoir fluid properties are selected for non-standardized discriminant function analysis, and the recognition rate can reach 92.8%. Two functions F1 and F2 with larger contribution rate are used to plot and set up the interpretation chart, and its return rate is 89%. The final interpretation chart was applied during 9 wells' 10 layer fluid interpretation and evaluation, obtained good effect with the coincidence rate 80%, and no valuable reservoirs were leaving out at the same time. The application in Huanxi-Pengyang area proves that Fisher discriminant method is suitable for similar reservoir fluid identification.
In order to explore the influence of loading modes on the scale effect law of shale strength and deformation, the shale outcrop of the seventh member of Yanchang Formation in Ordos Basin was cut into multiple scales for the triaxial compression, uniaxial compression and Brazilian splitting tests. The scale effect law and influence mechanism of shale strength and deformation under different loading modes were analyzed. The results show that: In the triaxial compression test, there are obvious differences in the scale effect law of shale strength and deformation between the regions with the ratio of height to diameter greater than 2 and less than 2. The critical height diameter ratio of rock samples whose end friction effect and heterogeneity play a leading role in the scale effect law of shale strength and deformation is between 0.4 and 0.8; In the uniaxial compression, the scale effect of shale strength and deformation is the most significant, followed by Brazil splitting, and triaxial compression is the least obvious. In triaxial and uniaxial loading of shale, there is no scale effect on the sectional deformation characteristics of stress-strain curve of rock sample, but in Brazilian splitting test, the sectional deformation characteristics of stress-strain curve of shale are various and the scale effect law is complex. Under three loading modes, there is no scale effect in shale failure mode. Heterogeneity, anisotropy and end friction are the basic reasons for the different scale effect laws of shale strength and deformation under different loading modes. The study of the scale effect law of shale strength and deformation under different loading modes can provide reference for choosing reasonable loading mode of rock sample, testing scale and determining mechanical parameters of rock mass in the mine.
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 oil recovery from N2 immiscible flooding and CO2 miscible flooding has little difference. The N2 flooding process can be divided into three stages: namely, the non-breakthrough stage, the early breakthrough stage and the mid-late breakthrough stage. The producing degrees from small pores is higher than that from large pores. However, the oil producing degree 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 producing degree 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 N2 injection in reservoir Chang 6 of the Ansai Oilfield.
Problems occur when drilling horizontal wells in tight gas reservoirs in the 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 drilling fluid system. After the study was completed, recommendations were made regarding forming a new optimized fast drilling technology for horizontal wells in tight gas reservoirs in the Sulige Gas Field. In 2019, this technology was applied in 56 wells in the 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 16.0%. The research and application showed that the key technology for horizontal wells drilling in tight gas reservoirs of the 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 tight gas reservoirs in the Sulige Gas Field.
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.
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.
To improve the rock-breaking efficiency of PDC bits and reduce stick-slip vibration, we developed a compound axial and torsional impact (CATI) drilling tool. The tool, which has the characteristics of simple structure and simultaneous action of the impact forces, makes the use of the energy from the self-excited oscillation pulse jet through a helical surface structure. Field applications have been carried out, and the results show that the tool has an excellent performance in increasing the penetration rate and extending the service time of PDC bit. Compared with conventional drilling, the penetration rate and single bit footage increased by 95.2%−193.8% and 46.4%−229.2%; the results are 66.3% and 194.0% when compared with axial impact drilling; the results are 30.2%−46.8% and 17.2%−191.8% when compared with torsional impact drilling; the penetration rate increased by 71.0% compared with the downhole motor. The results indicate that the tool improves rock-breaking efficiency by increasing the cutting depth, and reduces the stick-slip vibration in hard strata by increasing the cutting force. This study lays a foundation for the improvement and application of the compound axial and torsion impact drilling.
The interspaced adjustment wells were located in the fractured zone with high arranged well density, so many drilling technical problems were arise. For example, the more overflow and leakage appear in drilling, the safe drilling fluid density range is more difficult to determine, collapsing and stuck drilling that happened were caused by fracturing fluid intrusion, and the wellbore trajectory is more harder to design for avoiding fracture zone. To solve the above problems, the formation pressure of interspaced adjustment wells in fracturing zone was accurately analyzing, the safety drilling fluid density range was defined, the wellbore trajectory which could avoid fracture zone was designed, the plugging technology for interspaced adjustment wells and the control of both overflow and leakage was developed. The integration of the safety drilling technology for interspaced adjustment wells in Fuling shale gas field was used in 31 wells. The average horizontal section length is 1 933.25 m, the average drilling period is 52.38 d, and the average ROP is 10.31 m/h. In contrast of the past, the average drilling period was shorten by 10.66%, and the average ROP was improved 15.28%. This technology provide a strong technical support for the second productivity construction in Fuling Shale Gas Field, and which give reference for the similar shale gas field in both domestic and overseas.
Calcium carbonate scaling seriously hinders the sustainable development and utilization of geothermal energy. In order to provide scientific basis for the implementation of geothermal scale inhibition technology, the numerical simulation study on the scaling location of a geothermal Well XX in Boye, Hebei is conducted. The scaling depth prediction and analysis of influencing factors of geothermal well is presented using the WELLSIM software based on the geothermal well physical model. It is shown that, the simulated geothermal fluid temperature at the bottom of the well is 128.0 ℃. The pressure of geothermal fluids drops rapidly as they rise along the wellbore. At the depth of 56.1 m, the flash evaporation occurs here. The flashing depth moves down with the increase of CO2 concentration, NaCl concentration and geothermal fluid flow. What is more, the CO2 concentration has the greatest influence on the flashing depth. In the field of anti-scaling, the depth of the submersible pump or the filling depth of the scale inhibitor should be below the flash point of 56.1m. The flashing position can be adjusted by the wellhead pressure and flow rate to realize the collaborative optimization of geothermal mining and anti-scaling technology.
The Ordovician Santamu Formation in the Menshen 1 fault zone is characterized by mudstone, marl, fracture development and high risk of wellbore collapse. During drilling to 7 392.54 m of Santamu formation, the drilling meets the strike slip fracture zone, and the collapse is stuck, so it is difficult to deal with it. By analyzing the formation characteristics of Santamu formation, the high performance anti-collapse water-based drilling fluid technology is studied: mechanical support of well-wall through reasonable drilling fluid density, combin1ing filtration reduction technology measures are adopted to reduce the damage of filtrate to water-sensitive mudstone formation; multi-amino well-wall inhibitor is introduced to increase K+ content and achieve multiple anti-collapse effect; At the same time, the temperature resistance, lubricity and plugging performance of drilling fluid are improved to meet the requirements of inhibition, plugging, anti-collapse and high temperature stability of Santamu formation. The results show that the high performance anti-collapse water-based drilling fluid has remarkable anti-collapse effect, the K content remains around 35 000 mg/L, the high temperature and high pressure loss of 150 ℃ is reduced from 11.3 mL to 8.0 mL.
During the trial production of unconsolidated gas hydrate sediments in deep water, the decomposition of gas hydrate in a large area of unconsolidated formation may cause the collapse of overlying formation and the wellhead subsidence with the increase of the trial production time, resulting in the failure of trial production. The analysis model of seabed settlement and wellhead stability in the process of hydrate trial production in unconsolidated formation is established. It is considered that the negative friction and downhole load produced by hydrate decomposition are the main factors leading to wellhead instability. The finite element strength reduction method is used to simulate the influence of hydrate decomposition on formation settlement and wellhead stability. The results show that the negative friction around the pipe string is mainly distributed in the area about 1/3 upward from the bottom of the surface pipe after hydrate decomposition. Besides, the larger the hydrate decomposition radius and the higher the hydrate saturation, the greater the negative friction. The laboratory simulation test of the influence of hydrate decomposition on wellhead stability was carried out by using the self-developed wellhead simulation test device for gas hydrate production. The results showed that the relative error of the pull down load and negative friction resistance was within 10%, which verified the reliability of the calculation model and numerical simulation results. The research results can provide a theoretical reference for the control of the trial production time of hydrate in non-diagenetic formations in deep water and wellhead safety assessment.
There are persistent problems of unreasonable key parameters, immature fracturing technology, and low production 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 com-prehensive analysis fracturing effect of fractured wells. It focuses on improving the degree of complex fracture networks, increasing the volume of fracturing stimulation, and maintaining the long-term conductivity of fractures. A large-scale high-strength fracturing technology of volumetric fracturing for deep shale gas horizontal wells that focuses on“dense stage+short cluster spacing, equal size large hole perforation, sand fracturing with low viscosity slick water at high pumping rate, high strength proppant with small particle size combinations”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.
Jilh, Sudair and Khuff are encountered in the third vertical section in HWY block, Saudi Aramco. The scope of the depth is between 3 040 m and 4 150 m. The formation is mainly dolomite, limestone and carbonate which is hard and abrasive. The shale in the upper section is unstable and Serious block loss. So that much higher mud weight has to be used, which makes drilling more difficult and a low ROP. The conventional drilling method has not changed the low ROP, Drilling with down hole power tools such as motor has also no effect. Field tests show that the ϕ228 hydro-efflux hammer can effectively solve the problem of the low ROP on drilling hard formation. Based on the analysis of the rock compressive strength of the above formation, according to the relationship between the performance parameters of the hydro-efflux hammer and the rock drilling resistance parameters, combined with the application well design, the scheme of using ϕ228 Hydro-efflux hammer to increase the ROP is established, and the parameters of rotary percussion drilling are optimized. On this basis, the BHA and matching bit are further optimized, and the impact resistance and aggressiveness of matching bit are analyzed. It has been applied in hwy-116 well. The application results show that the speed-up effect of ϕ228 Hydro-efflux hammer is effective in ROP enhancement, which is 47% higher than the average ROP of adjacent wells. This successful application provides an effective technical means for increasing the ROP in the hard formation of the block.
Premature aging of packer 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., 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 reduce its Mooney viscosity, 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 integrated completion-acid fracturing, solved problems of deep oil and gas development in Tarim Basin, and had a good value for popularization and application.
Aiming at the problems of low warning efficiency and lagging monitoring technology in the frequent occurrence of domestic underground safety accidents, a downhole safety monitoring system with independent intellectual property rights was designed and implemented. The system processed real-time downhole parameters and monitoring data measured by sensors On-site drilling risk analysis and evaluation can effectively improve the safe drilling level of high-risk wells and high-cost wells under deep complex formation drilling conditions. After field tests, the system has perfect functions, stable performance, and the risk assessment accuracy rate is> 95%. It has partially reached or exceeded the technical level of similar foreign products on the measurement parameters of the same parameters. The experimental results show that the downhole safety monitoring system not only effectively solves the problems of low early warning efficiency of safety drilling accidents in deep complex formations, but also improves the drilling level and fills the domestic technological gap, which can produce greater economic benefits.
The Nanchuan Area is another shale gas production block of Sinopec after the first phase of Fuling shale gas production block. In order to further improve mechanical drilling rate and drilling efficiency of the shale gas horizontal well drilling in the block, carrying out technology research and optimization, such as well bore structure optimization, efficient bit optimizing, drilling borehole trajectory optimization, factory pattern, etc. on the basis of learning Fuling mature drilling experience and summarizing the problems existing in the shale gas drilling, finally formed a suitable drilling technology system for Nanchuan Area. The drilling technology system has been applied to over 30 wells in Nanchuan Pingqiao south area. The average drilling cycle has been shortened from 92.00 d to 79.67 d and the average reservoir penetration rate of high-quality reservoirs is over 98%. At the same time, more than 60 percent of the wells had a footage over 1,000 meters in one trip. On the basis, according to the drilling conditions in the JY10 Well block and Dongsheng Block with complex structure, this paper further analyzes the technical difficulties existing in the process of drilling acceleration and puts forward some suggestions to provide technical support for the subsequent production construction and efficient drilling in the area.