川西拗陷东部斜坡沙溪庙组气藏断砂配置及成藏差异性

Fault-sandbody configuration and accumulation differences of gas reservoirs in Shaximiao Formation,eastern slope of western Sichuan depression

四川盆地川西拗陷东部斜坡地区早期勘探表明侏罗系沙溪庙组油气显示频繁,而测试产量却比较低,属于丰度及效果都偏低且动用难度大的气藏,主要原因是断砂配置十分复杂,且成藏模式及关键的控制因素尚未明确。为此,通过对钻井和岩芯实验数据进行分析,深化对沙溪庙组气藏成藏地质条件研究,解剖3个典型气藏。研究结果表明:(1)气藏以断控成藏为主;(2)成藏的先决条件为通源断层;(3)河道砂体及断层的较佳配置关系是其充分必要条件。基于不同形变程度区对二者配置关系的整理,设立起中江、高庙子中—强变形区沙溪庙组“网状供烃、断砂输导、高效运移”的成藏模式,得到结论认为:(1)河道砂体与通源断层配置关系有“三型七类”,结合构造演化细分中—强形变区为三种动态断砂配置类型,即早期成藏后期保持型、早期成藏后期调整型和早期未有效成藏型;(2)成藏主控因素总结为“源、相、位”—即烃源情况、储层沉积相和气藏位于构造部位;(3)将沙溪庙组气藏划分为富集区、有利区和较有利区,把富集区作为下一步勘探开发的目标。在新认识的指导下获得勘探商业发现,并实现当年发现当年建产,已建成规模气田。

Early exploration for the eastern slope of the depression of western Sichuan Basin(western Sichuan depression for short)suggests that gas reservoirs in the Jurassic Shaximiao Formation reveals frequently oil-gas show,but relatively low test yield.They belong to hard-to-produce reservoir with low abundance and production.This is mainly attributed to very complex fault-sandbody configuration,and unclear models and controlling factors of gas accumulation.Based on the study of drilling and core experiment data,and geological conditions of gas accumulation,three typical gas reservoirs were analyzed in the Formation.The results show that the gas accumulation is dominantly fault-controlled;faults connecting to source are the prerequisite;and a good configuration between channel sand bodies and faults is a necessary and sufficient condition.According to the fault-sandbody configurations of areas with different deformation degrees,an accumulation model of network hydrocarbon supply,fault-sandbody transport and efficient migration in Shaximiao Formation was built for the moderate-strong deformation zones such as Zhongjiang and Gaomiaozi.Three conclusions are made:(i)There are“three types and seven classes”of configurations between channel sand bodies and source-connecting faults.The moderate–strong deformation zone can be divided into three types of dynamic fault-sandbody configuration by tectonic evolution,namely,early accumulation and late retention,early accumulation and late adjustment,and early ineffective accumulation.(ii)The main factors controlling gas accumulation are source rocks,sedimentary facies,and location of gas reservoir.(iii)Gas reservoirs in the Formation can be divided into enriched,favorable,and relatively favorable zones,and the enriched zone is taken as the target for exploration and development.Guided by this new understanding,commercial discoveries were made by exploration and put into production in the same year.Presently,large-scale gas fields have been built.