Petroleum Drilling Techniques is supervised by China Petrochemical Corporation (Sinopec Group), sponsored by Sinopec Research Institute of Petroleum Engineering.
It aims to serve the authors and readers interested in the field of petroleum, and promote the development of petroleum engineering technology. Its scope covers oil exploitation, oil drilling, and oil drilling equipment.
Petroleum Drilling Techniques is included in CSCD, CA, EBSCO. Impact factor is 1.650.
Since the geological conditions of the shale oil reservoirs in the Jiyang Depression are complex, there are many technical difficulties during the drilling and completion of horizontal wells, such as high safety risk, low rate of penetration (ROP), low efficiency of wellbore trajectory control, high complex efficiency, and poor cementing quality. The key technologies for the drilling and completion of horizontal shale oil wells in the Jiyang Depression were preliminarily developed, benefiting from the exploration and integrated application of optimization design of drilling engineering, ROP and efficiency enhancement for the horizontal wells, development of high-performance synthetic base drilling fluid, and cementing quality improvement for the horizontal wells. Moreover, these technologies were successfully applied to eight horizontal shale oil wells. The average total depth and average ROP were 4 402.60 m and 8.86 m/h, respectively, indicating that one-trip drilling was realized in the kilometric horizontal sections of horizontal shale oil wells in the Jiyang Depression and thus the complex efficiency was lowered significantly. This study can provide technical support for the effective development of shale oil resources in the Jiyang Depression and a reference for the exploration and development of other shale oil blocks in China.
Wellbore instability and excessive friction were encountered during drilling the ultra-long horizontal sections of horizontal wells in the shale oil reservoirs in Jimsar, Xinjiang. For safe and fast drilling of horizontal sections of 3 000–3 500 m, a friction reduction study was performed, such as optimization of the casing program, design of a dual two-dimensional wellbore trajectory, and determination of drilling parameters based on wellbore cleaning conditions. Moreover, an oil-based drilling fluid formula with excellent performance in inhibition, stability, and lubricity was identified in the laboratory. Finally, the key drilling techniques were developed for the horizontal wells with ultra-long horizontal sections in the shale oil reservoirs in Jimsar, Xinjiang. The techniques were applied in three wells with a rate of penetration of 10.9 m/h in the horizontal section and greatly reduced drilling time. The drifting, electric logging, and casing running in those wells were all successful in one trip, without any occurrence of downhole failure during drilling and completion. It set the longest horizontal section record of unconventional oil and gas reservoirs in China. Research and application results show that the techniques can meet the technical requirements for safe and efficient drilling of the horizontal wells with ultra-long horizontal sections in the Jimsar shale oil demonstration zone in Xinjiang and further improve the capacity for horizontal section extension, and it is worthy of popularization and application.
The use of volumetric fracturing technology can greatly increase the single-well production of shale oil in the Ordos Basin. Nevertheless, it is still difficult to achieve economic and effective development under the condition of low oil prices due to the fact that the technical thinking, technology mode and parameter system for volumetric fracturing are not reasonable enough. For this reason, according to field practice and laboratory test results of volumetric fracturing of shale oil at the Chang 7 Member of the Yanchang Formation in the Ordos Basin, Changqing Oilfield transformed the technical thinking for volumetric fracturing, thereby developing a technology mode of “large well clusters, long horizontal wells, dense cluster spacing, clustered perforation, soluble ball sockets, and variable-viscosity slickwater”. Then, the parameter system for volumetric fracturing was optimized. The mechanism of and key technologies for volumetric fracturing stimulation were systematically analyzed in light of the geological characteristics of the shale oil reservoir in the basin. The research results showed that the understanding of the seepage mechanism of shale oil in the reservoirs has gradually evolved from an effective displacement mechanism only for conventional reservoirs to a compound mechanism of effective displacement and oil-water imbibition displacement. The technology mode of volumetric fracturing proposed for the Ordos Basin was researched and developed independently, and its utilization obtained good field application results. In terms of improving the volumetric fracturing technology and obtaining higher productivity, some suggestions for the development of shale oil in the basin were put forward, including the further study of the mechanism of fracturing stimulation, optimization of key technical parameters, and development of volumetric fracturing visualization technology. The research results can provide a basis for the optimal design of volumetric fracturing of horizontal shale oil wells and can be used as a reference for the fracturing reconstruction of similar reservoirs.
The reasonable production system for enhanced fracture network stimulation was studied to maximize the cumulative production in the full period of horizontal continental shale oil wells in the Dongying Sag. According to the complex storage and seepage mechanisms of shale oil reservoirs, a model was built to characterize the full period of fracturing, shut-in, and production of two-phase flow in the dual media in shale oil reservoirs. Production variation with production system (different shut-in time and pressure drop rates in the flowing and pumping stages) and the method for production system optimization were preliminarily discussed by simulation. According to the simulation results, a reasonable production system for target wells was obtained. To be specific, the reasonable shut-in time was 60 d; the pressure drop rate was controlled to be 0.06–0.10 MPa/d at the early flowing stage and 0.02–0.04 MPa/d at the middle flowing stage; fluid-discharging production was carried out at the late flowing stage to rapidly release the oil pressure to 0; the pressure drop rate was controlled to ensure continuous production of oil wells at the pumping stage, avoiding insufficient fluid supply from the formation matrix due to excessively fast pressure drop. The research results can provide theoretical guidance for the development optimization of continental shale oil in the Dongying Sag and also provide references for the optimization of production systems for horizontal shale oil wells in other regions.
Staged fracturing technologies for horizontal wells are the key to the efficient development of shale oil. After more than a decade of research and practice, Sinopec has achieved major breakthroughs in shale oil exploration in several areas and has preliminarily developed the staged fracturing technologies for horizontal shale oil wells, which are characterized by ultra-tight spacing fractures, temporary plugging and diverting, high-concentration proppant injection, and reservoir protection. However, a gap still exists when compared with the process parameters and the technical level of the counterparts abroad. In this work, engineering geological characteristics of major shale oil blocks at home and abroad were compared, and the requirements and challenges for Sinopec’s shale oil fracturing technologies were analyzed. In addition, according to the characteristics of continental shale oil reservoirs, development suggestions on the fracturing technologies for shale oil with medium-high maturity and the in-situ upgrading technologies for shale oil with medium-low maturity were provided with respect to the research and implementation of integration of geology, development, and engineering, with consideration of economy and field operational feasibility. The suggestions can provide guidance in accelerating the building of a technical system for continental shale oil development and achieving the goal of economic development of shale oil.
Depending on the characteristics and the demands of exploration and development of continental shale oil reservoirs, Sinopec has carried out research on technologies for such reservoirs, including optimized and fast drilling and completion, logging evaluation, and reservoir stimulation. These new technologies, which have been successfully applied to 17 exploratory wells, strongly support the exploration and development evaluation of continental shale oil in a number of regions, such as Jiyang Depression, Biyang Sag, and Sichuan Basin. A major breakthrough was achieved in the exploration of shale oil in the Jiyang Depression. However, the shale oil engineering technologies of Sinopec still lag behind those of some foreign countries. Therefore, further research is still needed in technologies of multi-layer stereoscopic development by shale oil well factories, drilling of horizontal wells with ultra-long horizontal sections, and integration of shale oil geology and hydraulic fracturing. Sinopec’s research could thereby strive toward the perfection of the shale oil engineering technology system, the improvements in quality, speed, efficiency and output, and the beneficial development of continental shale oil.
