沁水盆地南部构造负反转、应力机制及油气意义

沁水盆地南部地区古生界高角度张性断裂极为发育,但至今仍未能很好地解释其形成及演化机制。本文依据区域构造演化背景分析、二维地震资料解释、岩石物理力学实验测试、产能数据及应力数值模拟结果,研究其形成机制。结果表明,研究区经历了3期构造旋回、4个构造演化阶段,华北板块整体处于大的挤压背景下,走滑拉分是典型的局部构造特征。负反转作用形成的高角度正断层造成了基底块断差异升降,产生了盆地内垒-堑相间分布的结果,由于地垒块体上升作用造成了石炭-二叠系形成了等厚横弯褶皱。在主生烃期,地层岩石易于发生近垂直的张性破裂,为区域垂直断裂的形成创造了条件。在区域强挤压构造环境下,可形成高角度逆断层;在伸展构造环境下,为构造负反转创造了条件。同时,该破裂型式也表明盆地具有一定的走滑拉分性质。古生界经历了2次构造负反转,分别为燕山中晚期(K1-K2)及喜马拉雅期(E-N)。燕山中晚期负反转的原因为盆地的弱伸展环境、由生烃作用所引发的张性破裂及地层剥蚀所导致的应力降低,该时期构造负反转程度较小。喜马拉雅期负反转的原因为盆地的强伸展环境、强烈的隆升剥蚀所造成的地层应力降低、温度大幅度降低产生的额外应力张量及地层岩石产生的张性应变量,该时期构造负反转程度较大。该区构造负反转对致密气储层的控"圈"、控"运"、控"储"及控"藏"效应明显。

Stress mechanism of negative inversion structures and its implication for oil and gas in Southern Qinshui Basin,China

Based on the analysis of regional tectonic background,interpretation of 2 dimensional seismic data,experimental testing of rock mechanics,data of production and numerical simulation of stress,the mechanism of nearly vertical faults developed in the Paleozoic strata in Southern Qinshui Basin are studied.It reveals that this area experienced 3 tectonic cycles and 4 stages of tectonic evolution.The North China plate was characteristic of compressive background,while strike-slip is the local structural features.The negative inversion of structures resulted from the formation of high angle normal fault caused lift and down of basement block,formed horst and graben in the basin.The uplift of horst resulted in the bending of Carboniferous and Permian strata.In hydrocarbon generation period,vertical tensile fractures occur easily in the rocks and provide condition for the formation of regional vertical normal faults and regional stretching environment provides conditions for the formation of negative inversion of structures.This area experienced 2 stages of structural negative inversion in the Palaeozoic strata,one is the early to mid Cretaceous,and the other is the Eogene to Neogene.The former is resulted from the weakly extensional environment.The effect of hydrocarbon formation leads to the occurrence of tensile fractures and the erosion of strata leads to the decease of stress.But the negative inversion of structures is weak in this period.Strong extension,occurrence of stress decease duo to extensive uplift of strata,occurrence of additional stress duo to temperature decrease and occurrence of tensile strain duo to strata and rocks in the Eogene to Neogene periods brings in the extensive negative inversion of structures.The negative inversion of structure affects obviously the trap,migration,accumulation and storage of oil and gas of the tight reservoir in the study area.