Tight gas reservoirs have become popular targets of the petroleum exploration in recent years. The Second Member of the Xujiahe Formation belongs to the typical tight gas reservoir which is characterized by low - super - low porosity and low - super - low permeability. Based on the research involving basin numerical simulation and diagenesis analysis, it is confirmed that the Second Member of Xujiahe Formation reached densifica-tion in the Middle Late Cretaceous. The densifying factors include vertical compaction, cementation and lateral tectonic compression. Different factors had different functioning time quantum, and reduced porosity in different degree. Before the Late Cretaceous, the main factors were vertical compaction and cementation, and the former was more significant. Since the Late Cretaceous, the lateral tectonic compression became the most important densifying-factor. Relatively high-quality reservoirs (RHQR) have developed on the background of generally tight sandstones. Their formation mechanisms include favorable deposition condition, abnormally high pressure, dissolution and early-forming of the chlorite, fracture generation and hydrocarbon filling. The favorable deposition condition was the precondition of forming RHQR. The abnormally high pressure in reservoir was a significant influence factor due to its inhibition on compaction. The constructive diagenesis was the prerequisite of developing RHQR. The forming fracture improved reservoir property especially after the reservoir turned to be tight.%致密砂岩储层成为近年来油气勘探的目标选区.川西坳陷中段须二段砂岩储层总体表现出低孔低渗—特低孔特低渗的特征,属于典型的致密砂岩气储层.通过盆地数值模拟、成岩作用分析研究得出须二段在晚白垩世中期达到致密化,其致密化因素包括垂向压实作用、胶结作用及侧向构造挤压作用.不同因素的作用时间段不同,且影响程度也不同.晚白垩世之前,致密化因素包括压实作用和胶结作用,且前者是主要因素；进入晚白垩世,侧向构造挤压成为后期的致密化因素.须二段储层在致密背景上发育相对优质储层,相对优质储层的发育机制包括有利的沉积条件、异常高压、溶蚀作用及早期绿泥石的生成、裂缝化作用及烃类充注等.有利的沉积条件是形成优质储层的前提；异常高压有效抑制了压实作用的进行,是优质储层发育的重要影响因素；建设性成岩作用对优质储层的发育起到了决定性作用；后期的裂缝化作用在储层致密化之后起到了改善储集性能的作用.
展开▼
