致密砂岩气聚集模型与定量模拟探讨

Geo-model of Tight Sandstone Gas Accumulation and Quantitative Simulation

将致密砂岩气聚集带划分为连续带和过渡带,并建立相应的地质模型。连续带位于构造低部位或斜坡处,砂岩直接覆盖在烃源岩之上,具有天然气大面积连续分布,上部不受盖层控制,下部无明显底水等特点;过渡带紧邻连续带,位于斜坡的上倾方向或构造较高部位,砂岩与烃源岩没有直接接触,天然气主要分布在储层物性相对较好的"甜点"中,天然气藏具有常规气和连续气2种特点。连续带以纳米级孔喉结构为特征,天然气运聚主要驱动力为生气产生的超压;过渡带以微米级孔喉结构为特征,天然气运聚主要驱动力为浮力。基于上述认识,建立"排挤式"和"置换式"致密砂岩气聚集数值模型。该模型在四川盆地合川地区的应用效果符合率达到90%,指出还有一半的天然气资源未被发现,主要分布在合川地区东北部、潼南地区北部和潼南地区东南部。

In this paper,we class the tight sandstone gas accumulation zone into continuous zone and transitional zone,and build the corresponding geological models.In general,the continuous zone,located at the relatively low position of the geological structure or the slope,is characterized as gas-bearing large area and continuous distribution,close association with source rocks,no limit by cap rocks,and lacking obvious bottom water.The transitional zone closes to the continuous zone but is located at the updip or the relatively high position of geological structure.Natural gases in the transitional zone conclude both conventional gas and continuous gas in the sweet spots.In the continuous zone,the nanopore composition makes the gas migration and accumulation depend on super-pressure action caused by gas generation,In contrast that the micron-pore and buoyancy drives the gas migration and accumulation in the transitional zone.Thus,we build two different numerical models of exclusion and displacement for tight sandstone gas accumulation.These models are used in the Hechuan district of the Sichuan basin and the coincidence rate of application effect reaches 90%,suggesting that half gas resources would be undiscovered in the north-east of the Hechuan area and the north and south-east of Tongnan area.