川东北元坝、马路背地区上三叠统须二段石英砂岩储层天然气产能差异的原因

摘要

Yuanba and Malubei are the main gas producing areas of the second member of Upper Triassic Xujiahe Fm (Xu 2 Member) in NE Sichuan Basin.In both areas,lithologic gas reservoirs composed of quartz beach bar facies strata are dominant,but their productivity is quite different.In this paper,the laws and differences of natural gas enrichment and high & stable yields of Xu 2 Member quartz sandstone reservoirs in both areas were discussed from the aspects of sedimentary environment,reservoir diagenesis and hydrocarbon accumulation conditions and patterns based on previous research results and newly collected assay data,seismic sections and logging data.It is shown that due to the restriction of quartz particle content of the rock itself and the fracturing scale,neither the sedimentation nor the reservoir diagenesis is the principal factor leading to the huge difference of Xu 2 Member natural gas enrichment between these two areas even though the sediments supplied by Dabashan provenance and the paleogeomorphy and hydrodynamic condition in the Malubei area are beneficial to the preservation of soluble interstitial materials and the strong tectonic movement in the Malubei area is conducive to the formation of fracture networks to enhance the reservoir connectivity.In the Malubei area,there are deep-source reverse faults with large fault displacement and vertical depth,and they connect the overlying Xu 3 Member source rocks with the Xu 2 Member reservoir and communicate marine source rocks,so natural gas can migrate laterally and vertically to quartz sandstone reservoirs continuously.Thus,the combined hydrocarbon accumulation model of "double hydrocarbon supplying and three dimensional migrating" is formed,and it is exactly the key factor contributing to the high and stable yields of Well M101 in this area.%元坝地区和马路背地区是四川盆地东北部(川东北)上三叠统须家河组二段的主要产气区,均为以石英滩坝相储层为主的岩性气藏,但二者的产能差异较大(前者低后者高).为此,基于前人的研究成果和新收集的分析化验、地震剖面以及测录井资料,从沉积环境、储层成岩作用和成藏条件模式等方面入手,探讨了上述两个地区须二段石英砂岩储层天然气的富集高产稳产规律及差异性.结果表明:①尽管大巴山物源区提供的沉积物质、马路背地区的古地貌和水动力条件等均有利于可溶填隙物保存,马路背地区经历的强构造运动也有助于形成网状裂缝提高储层的连通性,但受制于岩石本身石英颗粒含量和造缝规模程度,沉积和储层成岩作用均不能成为上述两个地区须二段储层天然气聚集存在巨大差异的主要因素;②由于马路背地区存在断距大、纵深远的深源逆断层,不仅使得上覆须三段烃源层与须二段储层对接,还沟通了下伏海相烃源层,天然气可以沿侧向+垂向持续向石英砂岩储层运移,形成“双重供烃、立体输导”的复式成藏模式,这才是该区M101井实现天然气高产稳产的关键因素.