摘要
为尝试研究非均匀层状岩层中的复杂水力压裂裂缝延伸行为,以胜利油田某典型砂泥薄互层储层的水平井压裂为背景模型,利用基于有限元的数值模拟软件,开展了一系列水平井压裂裂缝延伸行为的数值模拟研究。在模拟中,表征远场地应力的模型围压、层理(界面)的强度和地层岩性是考虑的主要因素。数值模拟表明,水力压裂裂缝的延伸模式是远场地应力、界面性质及地层岩性的综合作用结果。裂缝延伸过程中遇到层间界面会出现偏转、分叉和钝化终止行为,总体可分为4类延伸模式:直接穿透、钝化、T型扩展、偏转。这些非平面、复杂裂缝并非体积压裂改造裂缝,因此,不但不利于油气的流动,而且也是压裂压力畸高、有效主裂缝长度减少甚至压裂失败的原因之一。数值模拟初步解释了裂缝延伸过程中应力演化及其与层间界面的相互作用机制,可望为水力压裂改造工程相关的设计与机理分析提供参考。
As an attempt to more accurately capture the complex hydraulic fractures in heterogeneous and layered rocks,a series of simulations on the hydraulic fracturing near a horizontal well is performed using a FEM-based code,based on the characteristics of a typical thin and inter-bedded sedimentary reservoir in Shengli Oilfield. In the numerical simulations,confining stresses representing the effect of in situ stresses,strength of the interfaces,and material properties of the layers on either side of the interface are crucial in fracturing across interfaces between two adjacent rock layers. Numerical results show that the hydro- fracture propagation within a layered sequence of sedimentary rocks is controlled by the changing in situ stresses,interface properties,and lithologies. The path of the hydraulic fracture is characterized by numerous deflections,branchings,and terminations. Four types of potential interaction,i.e. penetration,arrest,T-shaped branching,and offset,between a hydro-fracture and an interface within the layered rocks are formed. Discontinuous composite fracture segments resulting from out- of-plane growth of fractures only provide a less permeable path for fluids,gas and oil,rather than forming a fracture network in volume fracturing techniques. These features are one of the sources of the high treating pressures and reduced fracture volume.Numerical results highlight supplementary information on the stress evolution related to the propagation of fracturesand the interaction of fractures,which may provide a meaningful guidance for field-scale problems related to the hydraulic fracturing engineering.
出处
《地下空间与工程学报》
CSCD
北大核心
2016年第6期1577-1585,共9页
Chinese Journal of Underground Space and Engineering
基金
国家自然科学基金(51479024)
关键词
水力压裂
岩石损伤
薄互层储层
层理
数值模拟
hydraulic fracturing
rock damage
thin interbedded reservoirs
bedding interface
numerical simulation
