上扬子地区断裂活动对页岩气保存的破坏作用

以四川盆地及周缘下古生界海相页岩层系断裂活动为研究对象,通过地震综合解释及对页岩层系裂缝方解石脉中流体包裹体的分析测试,结合不同含气性典型页岩气钻井解剖,开展了断裂活动对页岩气后期保存破坏作用的研究。断裂的级别及空间叠置方式、断裂活动的期次及其持续性对页岩气的保存条件具有重要的影响:①断裂级别越高其影响范围越大,距离一级断裂约10 km以内,保存条件破坏较大;距离二级断裂5 km以内,页岩含气性受影响明显;距离三级断裂2~3 km以内受一定影响;四级断裂影响不明显;②在井区断裂密度相似的前提下,不同级别的断裂从平行到小角度相交再到大角度相交,对页岩气保存的破坏作用逐渐增强;③断裂活动期次越多、持续时间越长对页岩气后期保存的破坏作用越强。根据断裂期次及活动持续性,可划分为4种类型:①晚燕山期短期活动,保存条件影响较小;②燕山期-早喜马拉雅期断续活动,保存条件受一定影响;③晚燕山期以来持续活动,保存条件破坏严重;④喜马拉雅期以来持续活动,保存条件影响较大。

Disruptive effects of faulting on shale gas preservation in Upper Yangtze region

The fracturing of the Paleozoic marine shale in the Sichuan Basin and its periphery was studied. The disruptive effects of faulting on shale gas preservation were analyzed based on the comprehensive interpretation of seismic structure, the analysis of fluid inclusions in calcite veins in fractures in shale layers, and the consideration of typical shale gas wells with different gas-bearing properties. Fault level, spatial stacking pattern, stage and duration have an important influence on the preservation conditions of shale gas. (1) The higher the fault level is, the larger the impact. The preservation conditions for shale gas are destroyed in the areas close to the first-level faults (within about 10 km), the second-level faults (within about 5 km), and the third-level faults (within about 2-3 km), but not influenced in the area close to the fourth-level faults. (2) Under the premise of similar fracture density in the well area, when different levels of faults intersect from parallel or small angles to large angles, the damage to shale gas preservation gradually increases. (3) The more fault activity periods and the longer their duration, the greater is the damage to shale gas preservation in the later period. Fault period and activity duration can be divided into 4 types:(1) short-term activity in the late Yanshan period, whose impact on preservation conditions was small; (2) intermittent activity in the Yanshan and early Himalayan periods where preservation conditions were affected to some extent; (3) continuous activity since the late Yanshan period, which caused serious damage to preservation conditions; and (4) continuous activity since the Himalayan period, which had a greater impact on preservation conditions.