断裂对川西坳陷致密砂岩气藏天然气运聚的控制作用

The Controlling of Fault on the Tight Sandstone Gas Migration and Accumulation in West Sichuan Depression

川西坳陷致密砂岩气藏的形成和分布受断裂控制作用明显。在对断裂的分布特征、断裂性质、断层几何特征、断裂形成时间等研究的基础上,结合研究区断裂与砂体的沟通关系、已发现气藏的开发情况和失利井的综合分析,揭示了断裂对陆相领域致密气藏天然气运聚的控制作用。研究结果表明,断裂影响和控制川西坳陷致密天然气藏有5种情况:断裂发育促使深层须家河组天然气富集成藏、断裂输导使深部须家河组天然气部分破坏、断裂输导深部须家河组天然气使中浅层侏罗系成藏、断裂破坏严重使中浅层侏罗系成藏效率低和断裂不发育的部位中浅层侏罗系含气性较差。单井与断裂距离的远近对单井产能具有一定的影响,且不同级别断裂影响规律存在较大差异:Ⅰ级断裂(延伸长度L≥100 km)和Ⅱ级断裂(10 km<L<100 km)对单井产能的影响具有类似的规律,中等距离有利于成藏,距离太短和太远产能均变低;Ⅲ级断裂(L<10 km)对天然气富集的控制作用明显,即总体上距离断裂越近,单井产能大,随着距离的变大,产能变小,一般单井离断裂距离>2 000 m,单井产能低。

The controlling of fault on the tight sandstone gas migration and accumulation of the continental strata in West Sichuan depression is very apparent.On basis of the research of the fault distribution characters,fault property,geometric characteristics,formation period,combined with the analysis of the connection of faults and sandstone,statistic of the developing wells state,the controlling factors of faulting on gas migration and accumu-lation are studied in detail.The research shows that five models can be identified by the controlling of fault on the tight sandstone gas.The first model shows that the fault growth prompted the natural gas accumulation in the tight sandstone in the deep strata of the Upper Triassic Xujiahe Formation reservoir.The second model indicates the fault development destroyed the natural gas reservoir in the deep strata of the Upper Triassic Xujiahe Forma-tion.The third model means that the faults transported the deep natural gas migrating and accumulating in the shallow Jurassic tight sandstone.The fourth model indicate the fault destroyed badly the natural gas reservoir in Jurassic tight sandstone.The last model shows the lack of fault growth is not good for the natural gas accumula-tion in the shallow Jurassic reservoir.The distance between the well and fault is also an important factor effec-ting the well production capacity.Different scale faults may create different gas accumulation.Scale I fault （spreads higher than 100 km）and ScaleⅡfault （spreads higher than 10 km and lower than 100 km）show the same regularity of medium distance between well and fault is most favorable for the gas accumulation,too far or too close is not good for gas reservoir.Scale Ⅲfault has the apparent positive controls that on the well produc-tion capacity increase with the increase of distance of well and fault.