川西南部地区中侏罗统沙溪庙组优质储层形成条件与控制因素

Formation conditions and controlling factors of high-quality reservoirs in the Middle Jurassic Shaximiao Formation of the southwestern Sichuan Basin

四川盆地西南部地区(以下简称川西南部地区)中侏罗统沙溪庙组具有优越的烃源和油气疏导条件,但多年来天然气勘探一直未获得重大突破。为了明确该区沙溪庙组优质储层及勘探有利区,指导下一步天然气的勘探部署,在对川西南部地区沙溪庙组物源特征、沉积相带展布、储层岩石类型与储集性能、成岩作用对储层影响等方面开展系统分析的基础上,指出了该区沙溪庙组致密砂岩气优质储层的形成条件和控制因素,进而落实沙溪庙组储层的有利分布区。研究结果表明:①该区沙溪庙组储层岩石类型以长石砂岩和岩屑长石砂岩为主,次为岩屑砂岩、长石岩屑砂岩,沉积受双物源控制,岩屑类砂岩物源来自西部龙门山,长石类砂岩来源于东北部米仓山—大巴山;②长石类砂岩储集性能明显优于岩屑类砂岩,纵向上长石类砂岩主要分布在沙二1亚段和沙二2亚段,横向上以东部地区最发育;③区内优质储层受沉积作用控制明显,河口坝、水下分流河道沉积的细—中粒长石砂岩物性最佳;④压实作用和胶结作用是沙溪庙组储层致密化、孔隙减小的主要因素,绿泥石胶结对原生孔隙具一定的保护作用,溶蚀作用是孔隙度增大的主要因素。结论认为,川西南部地区沙溪庙组三角洲平原分流河道、三角洲前缘水下分流河道及河口坝等相带的长石砂岩发育区是优质储层有利分布区,其中熊坡断裂以东地区,是下一步致密砂岩气勘探的重点方向。

The Shaximiao Formation of Middle Jurassic in the southwestern Sichuan Basin is advantageous in hydrocarbon sources and hydrocarbon migration conditions,but no significant breakthrough has been achieved in natural gas exploration here for many years.In order to define the high-quality reservoirs and favorable exploration areas of Shaximiao Formation in the southwestern Sichuan Basin and guide the natural gas exploration deployment in the following step,this paper systematically analyzes the provenance characteristics,distribution of sedimentary facies zones,reservoir rock types,reservoir performance,and diagenesis effect on reservoirs in the Shaximiao Formation of this area.And based on this,the formation conditions and controlling factors of high-quality reservoirs of Shaximiao Formation tight sandstone gas are clarified,and the favorable distribution areas of Shaximiao Formation reservoirs are defined.And the following research results are obtained.First,the reservoir rock types of Shaximiao Formation in this area are primarily feldspathic sandstone and lithic feldspathic sandstone and secondarily lithic sandstone and feldspathic lithic sandstone,and their sedimentation is controlled by double provenances with lithic sandstones from the Longmen Mountain on the west and feldspathic sandstones from Micang-Daba Mountain on the northeast.Second,the reservoir performance of feldspathic sandstones is much better than that of lithic sandstones.Feldspathic sandstones are mainly vertically distributed in the first and second sub-members of the second Member of Shaximiao Formation and laterally the most developed in the eastern area.Third,the high-quality reservoirs in this area are obviously controlled by sedimentation,and the fine-medium grained feldspathic sandstones deposited in the mouth bar and underwater distributary channel are the best in physical properties.Fourth,compaction and cementation are the main factors resulting in reservoir densification and porosity reduction in the Shaximiao Formation;chlorite cementation has a certain protective effect on primary pores;and dissolution is the main factor of porosity increase.In conclusion,the feldspathic sandstone development areas of delta plain channel,delta front underwater distributary channel and mouth bar facies in the Shaximiao Formation of the southwestern Sichuan Basin are favorable distribution areas of high-quality reservoirs,and the area to the east of Xiongpo fault is an important direction of tight sandstone gas exploration in the following step.