滇东恩洪区块地应力分布及深部煤层气临界深度预测

Distribution of in-situ stress and prediction of critical depth for deep coalbed methane in Enhong Block of eastern Yunnan region

我国滇东恩洪区块二叠系煤层气资源丰富,该区块是今后煤层气开发的重点区域之一,地应力分布对于储层压裂改造等煤层气开发工程具有重要影响。在注入/压降试井方法实测地应力约束下,基于Anderson修正模型对恩洪区块地应力分布进行预测,总体上,水平最大主应力SH,max、水平最小主应力Sh,min和垂向主应力Sv在不同深度段呈现不同应力机制类型,由浅至深依次表现为逆断型、走滑型和正断-走滑型。研究结果表明:在该区块二叠系宣威组内,地应力遵循SH,max≥Sv>Sh,min的关系,呈现正断-走滑型应力机制,而宣威组煤层地应力数值较其顶底板小,表现为正断型应力机制;岩石类型与埋藏深度影响地应力分布,水平主应力随埋藏深度的增加呈线性增大,杨氏模量小的煤岩,其水平地应力值最低;滇东恩洪区块深部煤层气临界深度约为700 m;研究结果可以为滇东恩洪区块煤层气开发提供新的地质参考。

The Permian layers in Enhong Block of eastern Yunnan region have abundant in coalbed methane resources,a potential key block for future coalbed methane development. It is well documented that in-situ stress distribution has significant impact on coalbed methane development projects such as hydraulic fracturing. In this study,the revised Anderson Model was employed to predict the stress distributions with in Enhong Block with the constraint from measured stress data from injection pressure decline approach. In general,the horizontal maximum principal stress (SH,max),the horizontal minimum principal stress (Sh,min) and the vertical stress (Sv) follow different stress mechanisms in different burial depths,which changes from reverse faulting stress regime,then strike-slip faulting stress regime and final normal to strike-slip faulting stress regime as the burial depth increases. The study results reveal: within this block of Permian Xuanwei Formation,the stresses have the relationship of SH,max≥Sv>Sh,min,indicating the existing of normal faulting to strikeslip stress regime. However,within this specific coal seams,stress magnitudes are relatively lower compared to those within the floor,showing the normal faulting stress regime. Due to the fact that burial depth and rock types have great impact on in-situ stress distribution.The horizontal stresses linearly increase along with burial depth;Furthermore,stress magnitude reaches the minimum in coal seams with lower Young’s Modulus. In Enhong Block,the critical depth for deep coalbed methane reservoir is about 700 m. The results from this study may provide new geological references for future coalbed methane development in Enhong Block of eastern Yunnan region.