1. College of Geosciences,China University of Petroleum (Beijing),Beijing　 102249,China; 2. State Key Laboratory of Petroleum Resources and Pro-specting, Beijing　 102249,China; 3. China Petroleum Exploration and Development Research Institute,Beijing　 100083,China

By analyzing the types of pressure curve,this paper evaluates the fracturing effect of the Shouyang block and Shizhuang block,and divides the proppant concentration curve types for the first time,revealing the statistical corre- spondence between the pressure and the proppant concentration curve types. Considering the types of in-situ stress,the difference of mechanical properties and stress between coal and surrounding rock,the influence mechanism of coal res- ervoir fracturing effect is analyzed. The study shows that:① The pressure curve can be divided into four types:de- scending,stable,rising and fluctuating,which is the direct basis for evaluating the effect of fracturing. ② The proppant concentration curve is divided into two types:continuous and discontinuous. It is found that there is a certain statistical correspondence between the pressure and the proppant concentration curve types. Its genetic mechanism is that in the weakly squeezed stress well layer (normal stress field),during the initial stage of proppant injection,the extension di- rection of the fracture is selected,sand plugging is easy to occur,more discontinuous proppant concentration curves are formed. And if the critical conditions of the vertical fracture to cut through the roof and bottom of the coal seam are sat- isfied,the vertical fracture will be vertically expanded to the surrounding rock,the different lithologic layers of the roof and bottom are cracked,the fluctuating pressure curve appears. If the critical conditions of the vertical fracture to cut through the roof and bottom of the coal seam are not satisfied,the vertical fracture will be limited to the inner side of the coal seam,and it is prone to different types of pressure curves of stable,descending and rising types. ③ Compared with the Shizhuang block,the Shouyang block has a double-high phenomenon of the discontinuous proppant concentra- tion curve and the fluctuating pressure curve types,and the overall fracturing effect is poor. The fundamental geological factor is that the stress state of the block determines that more wells develop vertical fractures that cut through the roof and bottom of the coal seam. ④ The proppant concentration curve can be used as an early warning curve for the fractu- ring effect. If the proppant concentration curve is discontinuous and the pressure curve begins to rise or fluctuate,the fracturing effect will be poor. And it may be considered to terminate the fracturing in advance.

国家科技重大专项资助项目(2016ZX05041-001，2016ZX05044-005)

SUN Tianzhu,KANG Yongshang,ZHANG Xiaona,et al. Evaluation of fracturing effect of coal reservoirs in Shouyang and Shizhuang CBM blocks and analysis of influencing mechanism[J]. Journal of China Coal Society,2019,44(10): 3125-3134.