多级压裂诱导应力作用下天然裂缝开启规律研究

Opening of Natural Fractures under Induced Stress in Multi-Stage Fracturing

刘雨 艾池

Liu Yu Ai Chi

中国石油大港油田分公司石油工程研究院, 天津 300280; 东北石油大学石油工程学院, 黑龙江大庆 163318

Petroleum Engineering Research Institute, PetroChina Dagang Oilfield Company, Tianjin, 300280, China; College of Petroleum Engineering, Northeast Petroleum University, Daqing, Heilongjiang, 163318, China

非常规储层多级压裂过程中,诱导应力是影响天然裂缝是否开启和压裂效果的重要因素。根据岩石力学理论和天然裂缝的受力状态,推导出压裂过程中地层应力分布计算模型,得到天然裂缝发生张性破坏和剪切破坏开启的力学条件。黑185井的模型计算结果表明:水平井压裂时存在诱导应力,由于诱导应力的影响,沿井筒方向的地应力增大1.70 MPa,地应力状态发生改变;考虑诱导应力的天然裂缝开启所需的压裂最小泵压为29.27 MPa;不考虑诱导应力的压裂最小泵压为26.31 MPa。研究结果表明,多级压裂产生的诱导应力使天然裂缝开启变得困难,诱导应力增大,天然裂缝开启所需的泵压增大,二者呈线性关系,实际压裂设计时应考虑诱导应力的影响。

During multi-stage fracturing in unconventional reservoirs, induced stress is the key factor in natural fracture opening and fracturing effets.The in-situ stress distribution analytical model was derived, and the mechanical conditions under which natural fractures initiated due to tensile failure and shear failure were obtained based on rock mechanics analysis.Stress distribution of Well Hei 185 by the model showed that induced stress existed in horizontal well fracturing and it made the in-situ stress along wellbore increased 1.70 MPa and the state of the in-situ stress changed.If induced stress was taken into account, minimum pump pressure required to activate natural fractures was 29.27 MPa rather than 26.31 MPa.The induced stress in multi-stage fracturing made the activation of natural fractures difficult.With the increase of induced stress, pump pressure to activate natural fractures increases, and there is a linear relation between induced stress and pump pressure.The induced stress should be considered into account in hydraulic fracturing design.

国家自然科学"基于混沌理论煤层气井压裂孔裂隙分形演化与渗流特征研究"(编号:51274067)资助。

https://doi.org/10.11911/syztjs.201501004