砂泥岩间互地层裂缝延伸规律探讨

目前裂缝预测主要集中在对开度、密度和发育强度等参数的半定量或定量化预测方面,对裂缝的延伸规律和穿透性研究缺少深入研究。针对这种情况,文中以天山山前某油田沙泥岩间互地层为例,采用应力场数值模拟法建立应力场与裂缝参数之间的定量关系,从而实现裂缝在沙泥岩间互地层中的的延伸规律与穿透性研究。模拟结果显示,越薄的砂岩层越容易产生构造裂缝,而砂岩厚度对砂岩中产生的裂缝在泥岩中的延伸长度影响很小,几乎可以忽略,且对延伸到泥岩中裂缝的孔隙度影响也不大,即不管泥岩上下砂岩层的厚度如何,延伸到泥岩中的裂缝孔隙度变化不大,均在038％左右;砂泥岩互层处裂缝在泥岩中延伸长度一般为15~2 m,当泥岩厚度为4 m左右时,砂岩裂缝恰好无法穿透泥岩,泥岩可作为有效的封盖层。

Discussion on the extension law of structural fracture in sand-mud interbed formation

In contrast to the present backdrop of fracture prediction mainly centering on the aperture,density and development of fracture with semi-quantitative and quantitative methods and less on extension law and penetrability,the paper,taking X oilfield as an example,adopts the stress field simulation to establish relationship between stress field and fracture parameters,then to research the extension law and penetrability of sandstone fractures into mudstone.Simulated result shows that the sandstone with thin thickness is easy to produce fractures,but the thickness of sandstone has little impact on extension distance and porosity of fractures in mudstone,which even can be neglected;that is to say,whatever the thickness of sandstone above or below the mudstone is,the porosity of fractures stretching into mudstone changes little,at about 0.38%.At the same time,fracture extension length at point of contact between sandstone and mudstone falls between 1.5—2 m;as mudstone thickness reaches 4 m,the fracture just can not penetrate through the mudstone,here the mudstone is thick enough to act as an effective cap formation.