Abstract: The complex gas-water relationship severely restricts the prediction of sweet spots and the deployment of well locations in tight sandstone gas reservoirs.In order to systematically study the controlling factors of gas and water distribution in sources-reservoir separated tight sandstone gas reservoirs, this study targets at Shaximiao Formation in central Sichuan Basin and combined with the core characteristics, reservoir physical characteristics, carbon isotope compositions of natural gas components, seismic and logging interpretations, as well as drilling and production data to analyze the source of natural gas in Shaximiao Formation reservoir and the macroscopic distribution and microscopic occurrence state of the fluid, and establishes the gas-water distribution pattern of the tight sandstone gas reservoir in Shaximiao Formation.The research results indicate that gas-producing, water/gas-producing and water-producing wells coexist in the southern part of central Sichuan (Zone A), while the reservoirs are gas-rich and water-free in the northern part of central Sichuan (Zone B), and the formation water is dominated by bound water.Natural gas from Xijiahe Formation on the eastern slope of western depression of Sichuan Basin, Xujiahe Formation in Zone A, Xujiahe Formation and Da’anzhai Member in Zone B migrated vertically to Shaximiao Formation through the middle and north section of Longquanshan fault, internal faults connected with source rocks, and Jiao① fault, respectively.Then oil and gas migrated laterally and accumulated along sand bodies in river channels.The occurrence state of reservoir fluids is controlled by the physical properties and pore structure of reservoirs.The porosity of gas reservoirs is generally greater than 7%, and fractures are well developed in water formation, showing high permeability (0.5 mD).The hydrocarbon source supply, faults connected with source rocks, and reservoir differences synergistically control the natural gas charging and saturation distribution in Shaximiao Formation, and dominate the pattern of gas-water distribution within the reservoirs.In Zone A, the tight reservoir exhibits an average gas saturation of 50.7%, characterized by favorable reservoir properties, where the free water content can reach 40% in partial areas, and some wells produce water.In Zone B, the tight reservoir exhibits an average gas saturation of 55.8%, with relatively poor reservoir properties and high bound water saturation, and wells only produce gas rather than water.Additionally, the complex gas-water distribution in Zone A is also influenced by the cooperative adjustment of low-amplitude nose-shaped uplift structures and faults.

Key words: tight sandstone gas reservoirs, source-reservoir separation, gas-water distribution, main control factors, central Sichuan Basin, Shaximiao Formation

摘要： 复杂的气水关系严重制约着致密砂岩气藏的"甜点"预测与井位部署。为系统研究源-储分离型致密砂岩气藏中气水分布的控制因素,以四川盆地中部(川中)地区沙溪庙组为研究对象,结合岩心特征、储层物性特征、天然气组分的碳同位素组成、地震与测井解释以及钻井生产资料等,分析了沙溪庙组储层内天然气的来源以及流体的宏观分布规律和微观赋存状态,建立了川中地区沙溪庙组致密砂岩气藏的气水分布模式。研究结果表明:川中地区南部(A区)产气井、产水/气井和产水井并存,而川中地区北部(B区)整体富气且不产水,地层水以束缚水为主;来自川西凹陷东坡须家河组、A区须家河组以及B区须家河组和大安寨段的天然气分别通过龙泉山断裂中—北段、区内通源断裂和角①断裂垂向运移至沙溪庙组,然后沿河道砂体侧向运聚成藏;储层物性和孔隙结构控制着储层流体的赋存状态,气层的孔隙度普遍大于7%, 水层中裂缝发育且渗透率高(0.5 mD)。烃源供给、通源断裂和储层差异三者协同控制着川中地区沙溪庙组的天然气充注范围和含气饱和度分布,主导着储层内气水分布的平面格局。A区致密储层的含气饱和度平均为50.7%, 储层物性较好,局部自由水含量达40%, 部分钻井产水;B区致密储层的含气饱和度平均为55.8%, 储层物性差,束缚水饱和度高,钻井只产气而不产水。此外,A区复杂的气水分布关系还受低幅鼻状隆起构造与断裂的协调影响。

关键词: 致密砂岩气藏, 源-储分离, 气水分布, 主控因素, 四川盆地中部, 沙溪庙组