Discussion of hydraulic fracturing technical issues in shale oil reservoirs
SHI Lin , ZHANG Kunpeng, MU Lijun
1 China Petroleum Drilling Engineering Research Institute, Beijing 102206, China 2 State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China 3 MOE Key Laboratory of Petroleum Engineering in China University of Petroleum, Beijing 102249, China 4 PetroChina Changqing Oilfield Company Oil and Gas Technology Research Institute, Xian 710018, China
Many pilot tests on the efficient development of unconventional oil have been carried out in Changqing, Jimsar and other regions of China, and good results have been achieved. In 2019, some of the reservoirs in the above areas were named shale oil reservoirs, which aroused widespread attention at home and abroad. Expanding the scope of the definition of shale oil will help improve the efficiency of unconventional oil and gas development. However, compared with the development of shale gas reservoirs, there are still some theoretical and technical shortcomings in the efficient development of shale oil reservoirs. In this way, research and discussion of the challenging concepts and engineering problems of hydraulic fracturing of some shale oil reservoirs at home and abroad have been carried out, and the following main understandings have been obtained: (1) Based on the bedding development and shale content of shale, establishing targeted stimulation technology is of positive significance to the efficient development of shale oil reservoirs; (2) Increasing fracturing fluid volume, displacement, sand volume, and hydraulic fracture density are the current effective measures to improve the effect of shale oil reservoir hydraulic fracturing treatment. Injecting sufficient liquid and sand to the targeted area is the goal of the reservoir hydraulic fracturing treatment. Therefore, the water function coefficient can replace the traditional stimulated reservoir volume and other concepts as the basis for its design and optimization. In addition, the exploration and development strategies of deep and shallow shale oil reservoirs should be treated differently; (3) When designing the horizontal wellbore orientation, it is not necessary to stick to the direction perpendicular to the maximum principal stress, because the fracturing fluid entering the formation will affect the in-situ stress field. The weak structures such as bedding structures and natural fractures will lead to the development of fractures. Therefore, the distribution mode and development degree of special structures such as natural fractures and bedding, the characteristics of the in-situ stress field, and the interaction between the fracturing fluid and the in-situ stress field should be considered comprehensively. (4) The technical concept of vigorously promoting the replacement of ceramsite with quartz sand has a good effect in reducing cost and increasing efficiency of shale oil reservoirs and has already achieved good results in shale oil and gas development. However, there is a need for a more complete evaluation method of the proppant’s influence on the conductivity of the fluid under complex fracture conditions, so as to objectively support the development of technology.
