蜀南观音场地区须家河组砂岩致密化与成藏匹配关系

Matching between sandstone tightening and hydrocarbon accumulation of the Xujiahe Formation,Guanyinchang area in southern Sichuan Basin

蜀南观音场地区须家河组储层主要为一套三角洲平原分流河道砂体。对储层成岩作用的描述及致密化原因分析认为：沉积时水动力强弱决定了砂体储集性能的好坏，强烈的机械压实作用是原生孔隙大量损失的主要原因，成岩期石英次生加大是砂岩储层致密的关键因素。砂岩中石英次生加大边包裹体温度分布在82.5～125.1℃，推算致密化深度介于1725～2864 m，发生在燕山构造活动期间。根据研究区须家河组砂岩储层致密化过程与成藏运聚期次分析，认为：初次成藏期，砂岩储层未致密，天然气可以横向长距离运移；成藏高峰期前，砂岩储层已经致密，天然气不能横向长距离运移，以河道不整合面和高压开启的微裂缝作为运移通道；喜山期定型为现今的构造-岩性复合气藏，气藏受岩性、构造共同控制，非均质性强。

Tight sandstone reservoir of the Xujiahe Formation in Guanyinchang area mainly consists of delta plain distribu-tary channels sandbodies .Based on analyses of reservoir diagenesis and tightening ,detailed study shows that the hydrody-namic conditions during sedimentation determine the storage capacity of reservoirs .Strong compaction is the major factor causing the decrease of inter-particle primary porosity ,and quartz overgrowth in diagenetic stage is the key factor causing the tightening of reservoir .The temperatures of fluid inclusions in quartz overgrowth is between 82.5-125.1 ℃,accor-ding to which the tightening depth is estimated to be between 1 725-2 864 m.This depth interval corresponds to the pe-riod of Yanshan movement .According to analysis of the tightening process and hydrocarbon accumulation stages in the Xujiahe Formation sandstone reservoir ,the following understandings were obtained .The sandstone reservoir was not tight-ened at the initial phase of gas accumulation ,so gas could migrate long distance laterally .Before the peak gas accumula-tion,the sandstone reservoir had become tight ,thus the gas could not migrate laterally for a long distance ,instead,they migrated along the unconformity of channel and microfractures opened by high pressure .of the composite structural and lithologic gas reservoir got finalized during Himalayan epoch ,and the gas reservoir was controlled by both lithology and structures ,so their heterogeneity was strong .