Abstract：Strengthening the interaction between hydraulic fractures and natural fractures by the adjustment of pump pressure is the key of fracture network. Longmaxi shale outcrops are selected to study the propagation of hydraulic fractures and the interaction between hydraulic fractures and natural fractures by utilizing tri-axial fracturing test system. The pump pressure increases in a step-wise manner during the tests. The experimental results indicate that the variable pump rates can gradually build the pressure, which generates many under-fracture points in weak planes around the wellbore. Hydraulic fractures will have dynamic extension along these under-fracture points when there is a sudden increase of pump rate. As the pump rate increases in a step-wise manner, the pump pressure significantly increases. Higher pump rate leads to a more fluctuant pump pressure and a more complex fracture network. The occurrence and geometric distribution of natural fractures and net pressure can influence the degree of further interaction. The results prove that the variable pump rates can activate more natural fractures, which contributes to form complex fracture network.
[1] DANESHY A A. Hydraulic fracture propagation in the presence of planes of weakness[R]. SPE 4852, 1974. [2] WARPINSKI N R, TEUFEL L W. Influence of geologic discontinuities on hydraulic fracture propagation[J]. Journal of Petroleum Technology, 1987, 39(2): 209-220. [3] RENSHAW C E, POLLARD D D. An experimentally verified criterion for propagation across unbounded frictional interfaces in brittle, linear elastic materials[J]. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1995, 32(3): 237-249. [4] ZHOU J, XUE Cheng-jin. Experimental investigation of fracture interaction between natural fractures and hydraulic fracture in naturally fractured reservoirs[C]// Annual of Conference Exhibition and Society of Petroleum Engineering, 2011. [5] ZHOU Jian, CHEN Mian, JIN Yan, et al. Analysis of fracture propagation behavior and fracture geometry using a tri-axial fracturing system in naturally fractured reservoirs[J]. International Journal of Rock Mechanics and Mining Sciences, 2008, 45(7): 1143-1152. [6] TALEGHANI A D, OLSON J E. Numerical modeling of multistranded-hydraulic fracture propagation: Accounting for the interaction between induced and natural fractures[J]. SPE Journal, 2011, 16(3): 575-581. [7] TALEGHANI A D. Modeling simultaneous growth of multi-branch hydraulic fractures[C]// ARMA. San Francisco, 2011. [8] GU H, WENG X. Criterion for fractures crossing frictional interfaces at nonorthogonal angles[C]// ARMA. Salt Lake City, 2010. [9] CHENG Wan, JIN Yan, CHEN Mian, et al. A criterion for a hydraulic fracture crossing a natural fracture in a 3D space and its field application[J]. Petroleum Exploration & Development, 2014, 41(2): 1-6. [10] ZHAO Hai-feng, CHEN Mian, JIN Yan, et al. Rock fracture kinetics of the fracture mesh system in shale gas reservoirs[J]. Petroleum Exploration and Development, 2012, 39(4): 465-470. [11] 陈 勉. 页岩气储层水力裂缝转向扩展机制[J]. 中石油大学学报（自然科学版）, 2013,37(5): 88-94. (CHEN Mian. Re-orientation and propagation of hydraulic fractures in shale gas reservoir[J]. Journal of China University of Petroleum. 2013, 37(5): 88-94. (in Chinese)) [12] 柳贡慧, 庞 飞, 陈治喜. 水力压裂模拟试验中的相似准则[J]. 石油大学学报（自然科学版）, 2000, 24(5): 45-50. (LIU Gong-hui, PANG Fei, CHEN Zhi-xi. Fracture simulation tests[J]. Journal of China University of Petroleum. 2000, 24(5): 45-50. (in Chinese))
