基于拓扑结构的岩石裂缝网络表征方法

摘要

The inter-fracture connection state has a direct effect on the properties of a fracture network,such as continuity and connectivity.However,the existing rock fracture network characterization model fails to describe the connection state accurately.In this paper,the basic parameters of a topological structure for a fracture network were defined by means of a topological method,the number of fractures and branches and the average amount of connection points of fractures and branches were calculated by counting the number of various nodes,and accordingly a topological structure model was established of the fracture network describing the connection degree of fractures quantitatively.Then,this topological structure model was combined with the Pxy system model used for fracture network characterization,the comprehensive fracture network evaluation index and its expression form were defined,and a new method was developed for characterizing the rock fracture network based on the topological structure.Finally,this method was applied to characterize the shale fracture network in the first and second members of Qingshankou Fm,the Lower Cretaceous in the southern Songliao Basin.The characterization results are more comprehensive.It is concluded that this method can describe both the development degree and connectivity of a fracture network so as to characterize the rock fracture network sufficiently.Therefore,it plays a useful role in reservoir evaluation,reservoir stimulation and hydrocarbon seepage.Besides,for lack of quantitative characterization between topological structure parameters,comprehensive evaluation index and rock fracture network properties,lots of testing work will still be required in the next step.%裂缝间的联结状态直接影响着裂缝网络的连续性、连通性等性能,而现有的岩石裂缝网络表征模型又无法准确描述裂缝间的联结状态.为此,运用拓扑方法,定义了裂缝网络拓扑结构基本参数,通过统计不同类型节点数的方式,计算了裂缝数、分支数以及裂缝、分支平均连接点数,由此建立了可以定量描述裂缝联结程度的网络拓扑结构模型.在此基础上,将该拓扑结构模型与表征裂缝网络的Pxy体系模型相结合,定义了裂缝网络综合评价指数及其表达形式,建立了一种基于拓扑结构的岩石裂缝网络表征方法.最后,应用该方法对松辽盆地南部下白垩统青山口组一段、二段页岩裂缝网络进行了表征,取得了较为全面的表征结果.结论认为:①该方法既可以描述裂缝网络的发育程度,又可以描述裂缝网络的连通性能,能够更为充分地表征岩石裂缝网络,对储层评价、储层改造、油气渗流等研究工作具有一定的帮助;②由于拓扑结构参数、综合评价指数与岩石裂缝网络性能之间的定量刻画尚不清晰,故下一步还需要开展大量的测试工作.