Su Yuliang, Ren Long, Meng Fankun, Xu Chen, Wang Wendong
School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shandong, P. R. China.
PLoS One. 2015 May 12;10(5):e0125319. doi: 10.1371/journal.pone.0125319. eCollection 2015.
Stimulated reservoir volume (SRV) fracturing in tight oil reservoirs often induces complex fracture-network growth, which has a fundamentally different formation mechanism from traditional planar bi-winged fracturing. To reveal the mechanism of fracture network propagation, this paper employs a modified displacement discontinuity method (DDM), mechanical mechanism analysis and initiation and propagation criteria for the theoretical model of fracture network propagation and its derivation. A reasonable solution of the theoretical model for a tight oil reservoir is obtained and verified by a numerical discrete method. Through theoretical calculation and computer programming, the variation rules of formation stress fields, hydraulic fracture propagation patterns (FPP) and branch fracture propagation angles and pressures are analyzed. The results show that during the process of fracture propagation, the initial orientation of the principal stress deflects, and the stress fields at the fracture tips change dramatically in the region surrounding the fracture. Whether the ideal fracture network can be produced depends on the geological conditions and on the engineering treatments. This study has both theoretical significance and practical application value by contributing to a better understanding of fracture network propagation mechanisms in unconventional oil/gas reservoirs and to the improvement of the science and design efficiency of reservoir fracturing.
致密油藏中的人工裂缝控制储量（SRV）压裂常常会引发复杂裂缝网络的生长，其形成机制与传统的平面双翼裂缝有着根本的不同。为揭示裂缝网络扩展的机制，本文采用改进的位移不连续法（DDM）、力学机制分析以及裂缝网络扩展理论模型的起裂与扩展准则及其推导。通过数值离散方法获得并验证了致密油藏理论模型的合理解。通过理论计算和计算机编程，分析了地层应力场、水力裂缝扩展模式（FPP）以及分支裂缝扩展角度和压力的变化规律。结果表明，在裂缝扩展过程中，主应力的初始方向发生偏转，裂缝尖端周围区域的应力场变化剧烈。理想裂缝网络能否产生取决于地质条件和工程处理措施。本研究对于更好地理解非常规油气藏裂缝网络扩展机制以及提高油藏压裂科学与设计效率具有理论意义和实际应用价值。
