川西坳陷根缘气藏异常地层压力

典型根缘气的成藏服从活塞式运聚原理,气水之间的整体推移式排驱作用在机理上产生高异常地层压力。在致密的储层条件下,根缘气藏中的天然气渗流受阻,当地层发生抬升或沉降运动时,地层压力的调整需要较之常规储层气藏更长的时间,从而形成了原始地层压力较长时间地滞留。川西坳陷根缘气发育,其中区域性分布的高异常地层压力为根缘气成藏的直接产物之一,区域上的高异常地层压力除与根缘气成藏直接有关外,还与根缘气成藏前的欠压实作用及成藏后的区域性构造抬升有关。由于地层流体的系统封闭性较好,现今的高异常地层压力为三阶段演化及三级升压作用叠加的结果,即晚侏罗世中晚期之前欠压实及生烃等作用、晚侏罗世中晚期至古近纪中晚期热裂解生气及根缘气成藏作用、古近纪中晚期以后区域地层抬升导致压力滞留及相对升压等多阶段、多因素的综合作用。从异常地层压力变化的剖面结构及计算结果分析,1.42的压力系数主要为成藏期后的区域构造抬升等因素所贡献,更高的压力系数则主要由根缘气成藏所产生。根据这一界限,大致可以确定根缘气的发育范围。

Abnormal pressure in the source-contacting gas reservoir in western Sichuan basin

The migration and accumulation of typical source-contacting gas that is also called basin-centered gas,follow the piston principle that generates super pressure essentially.In the tight reservoir,the formation water cannot exchange sufficiently,which makes the pressure in gas pools maintained longer than that in conventional reservoir pools when the pools is subject to uplift or subsidence.The western Sichuan depression is one of the depressions whose source contacting gases were studied earliest in China,where the regional hyper-pressure is the direct product and the sign of the accumulation of source-contacting gas.Besides the effect from the accumulation of source-contacting gas,the regional overpressure in the western Sichuan depression is related directly to the undercompaction and regionally tectonic uplift before or after the accumulation of source-contacting gas.Present regional overpressure in the western Sichuan depression comes from three phases of tectonic movements and three stages of generation of abnormal pressure owing to the preferable obturation of petroleum accumulation systems.The multiple stages and multiple causes of the pressure rising may be delineated as follows:the undercompaction and hydrocarbon generation before the late Jurassic;the gas generation and accumulation of source-contacting gas from the late Jurassic to the Eogene;and the regional uplift after the late Eogene.Indicated by section configuration and calculated emendation,the coefficient of abnormal pressure in the western Sichuan depression may be divided into the contribution mainly from regional uplift,which is some 1.42,and that mainly from the accumulation of source-contacting gas,which contributes most of the rest over-pressure.According to the isoline of the pressure coefficient that is 1.42,the distribution of source-contacting gas accumulations can be determined approximately.