鄂尔多斯盆地东北缘太原组—山西组现今地应力预测及其对煤层气开发的影响效应

Prediction of current in-situ stress in Taiyuan-Shanxi Formations of northeastern Ordos Basin and its impact on coalbed methane development

  • 摘要: 鄂尔多斯盆地东北缘太原组—山西组作为煤层气勘探开发的重点层系,其地应力状态是影响储层渗透性及压裂改造效果的关键因素。为揭示煤储层现今地应力状态及其主控地质因素,并分析其对储层渗透性与压裂改造的工程控制效应,以区内太原组—山西组主采煤层(4+5#及8+9#煤层)为研究对象,采用注入—压降测试、差应变地应力测试、三轴岩石力学实验以及测井资料解释等多种方法,对研究区现今地应力特征开展研究。结果表明:研究区(4+5#及8+9#煤层)以正断型应力机制为主导;地应力随埋深增加显著增大,其空间非均质性主要受岩性及岩石力学性质控制,煤层段地应力值显著低于其顶底板致密岩层,在4+5#和8+9#煤层中分别形成了显著的水平主应力差。正断型应力机制作用下,高角度裂隙多呈开启状态,有利于提高煤储层渗透性。压裂改造方面,推测压裂缝以垂向扩展为主导模式。系统阐明了鄂尔多斯盆地东北缘太原组—山西组煤储层现今地应力垂向分布规律及其对储层开发的关键影响,以期为该区煤层气井网部署、压裂设计及开发策略优化提供地质力学依据。

     

    Abstract: The Taiyuan-Shanxi formations at the northeastern margin of the Ordos Basin is a key strata for coalbed methane (CBM) exploration and development, and its in-situ stress state is a key factor influencing reservoir permeability and the effectiveness of hydraulic fracturing. To reveal the current in-situ stress state of the coal reservoirs and its main controlling geological factors, and to analyze its engineering impacts on reservoir permeability and hydraulic fracturing, the main coal seams (4+5# and 8+9#) of the Taiyuan-Shanxi formations in the area were taken as the research object. Multiple methods, including injection-falloff tests, in-situ stress tests with differential strain analysis, triaxial rock mechanics experiments, and well logging interpretation, were used to study the current in-situ stress characteristics of the study area. Results indicated that the 4+5# and 8+9# coal seams in the study area were dominated by a normal faulting stress regime. In-situ stress increased significantly with burial depth, and its spatial heterogeneity was primarily controlled by lithology and rock mechanical properties. The in-situ stress values in coal seams were markedly lower than those in dense roof and floor plates, forming significant differences in horizontal principal stress in the 4+5# and 8+9# coal seams. Under the normal faulting stress regime, high-angle fractures were mostly open, which was favorable for improving coal reservoir permeability. In terms of hydraulic fracturing, it was inferred that fractures mainly propagated vertically. This study clarifies the vertical distribution pattern of current in-situ stress in coal reservoirs of the Taiyuan-Shanxi formation at the northeastern margin of the Ordos Basin and its key influence on reservoir development. Expected to provide a geomechanical basis for CBM well pattern deployment, fracturing design, and development strategy optimization in this area.

     

/

返回文章
返回