砾岩油藏压裂裂缝遇砾扩展行为机理  被引量:10

Propagation mechanism of fractures caused by hydraulic fracturing when encountering gravel in conglomerate reservoirs

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作  者:徐泽昊 刘向君[1] 梁利喜[1] 丁乙[1] 熊健[1] 段茜 XU Zehao;LIU Xiangjun;LIANG Lixi;DING Yi;XIONG Jian;DUAN Xi(National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu City,Sichuan Province,610500,China)

机构地区:[1]西南石油大学油气藏地质及开发工程全国重点实验室,四川成都610500

出  处:《油气地质与采收率》2023年第3期115-127,共13页Petroleum Geology and Recovery Efficiency

基  金:国家科技重大专项“砂砾岩致密油岩石力学特征描述与建模”(2017ZX05070-001)。

摘  要:砾石的随机分布使砾岩储层具有高度非均质性,显著影响局部力学响应,难以控制和预测水力压裂裂缝的扩展。水力压裂裂缝的遇砾扩展机制仍不清楚,使得水力压裂的设计和有效实施充满挑战。基于全局黏聚力单元,在Abaqus平台建立了渗流-应力-损伤多场耦合的二维裂缝扩展模型;在细观尺度上将砾岩视为砾石、基质和胶结面组成的三相复合材料,进行压裂裂缝遇砾扩展行为机理研究。结果表明,水力裂缝遇砾发生穿砾、绕砾、穿砾且绕砾等现象;砾石的渗透性和弹性模量对裂缝遇砾行为影响的作用机理不同:砾石的低渗透性造成憋压现象,裂缝尖端流体压力提高了13%,水平与竖直方向有效应力分别减小了10.1%和12.8%;砾石的高弹性模量造成应力的屏蔽现象,裂缝尖端与砾石间的区域水平方向有效应力减小了5.8%。砾石的低渗透性与高弹性模量都会造成胶结面上发生剪应力集中,增加了胶结弱面破坏的可能性,造成裂缝遇砾发生偏转。The random distribution of gravel makes conglomerate reservoirs highly heterogeneous,which significantly affects the local mechanical response and makes it difficult to control and predict the propagation offractures caused by hydraulic fracturing.The propagation mechanism offractures caused by hydraulic fracturing when encountering gravel remains unclear,which makes the design and effective implementation ofhydraulic fracturing challenging.In this pa­per,based on the global cohesion element,a two-dimensional(2D)fracture propagation model with flow-stress-dam­age multi-field coupling is established on the Abaqus platform.The conglomerate rocks are regarded as a three-phase composite material composed of gravels,matrix,and cemented surfaces on a mesoscopic scale,and the propagation mechanism of fractures caused by hydraulic fracturing when encountering gravel is studied.The results show that frac­tures caused by hydraulic fracturing penetrate and bypass gravel in conglomerate reservoirs.The permeability and elastic modulus ofgravel have different effects on the behavior offractures encountering gravel.The low permeability ofgravel causes thepressure holding,and the fluidpressures atthe crack tips increase by 13%;the effective stresses inhorizontal and vertical directions decrease by 10.1%and 12.8%,respectively.The high elastic modulus of gravel results in stress shielding,and the effective stresses in the horizontal direction ofthe area between the tip and the gravel are reduced by 5.8%.The lowpermeability and high elastic modulus ofgravel both cause shear stress concentration on the cemented sur­face,which increases the possibility ofdamage to the weak cemented surface and makes fractures bypass gravel.

关 键 词:砾岩 砾石 水力压裂 多场耦合 数值模拟 裂缝扩展 

分 类 号:TE357.1[石油与天然气工程—油气田开发工程]

 

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