川东北元坝地区须三段钙屑砂岩储层特征及控气因素

Characteristics of calcarenaceous sandstone reservoirs and gas accumulation control factors of the 3^(rd) Member of Xujiahe Formation in Yuanba area,Northeast Sichuan Basin

川东北元坝地区须家河组三段已获千亿方预测储量,具有良好的勘探开发潜力,但其储层特征及控气因素不明确。利用岩心、薄片、物性等分析测试资料,采用井震结合的方法,对该区须三气藏及主要目的砂组的储层特征及控气因素进行了研究。研究认为,须三段以辫状河三角洲平原-三角洲前缘亚相沉积为主,钙屑砂岩具有碳酸盐岩岩屑含量高、石英含量低的特点,测井上显示低伽马、高电阻的特征。(含砾)钙屑砂岩储层总体上为特低孔-特低渗储层,储集空间类型多样,以溶蚀孔及其中的自生矿物晶间孔为主,(微)裂缝为辅;溶蚀孔隙主要分布于钙屑颗粒粒间,连通性好,是优质储层的最重要的储集空间。三角洲平原-前缘亚相的高能分流河道含砾钙屑砂岩、钙屑砂岩、砂砾岩有利岩相是天然气富集和高产的先决条件。沿层间发育的平缝和低角度缝及沿裂缝发育的溶蚀孔隙是天然气富集和高产的决定性因素,构造和断裂是天然气的富集和高产的重要条件。

The 3rdMember of Xujiahe Formation（ T3x3） has great petroleum exploration potential and its predicted gas resource volume is a hundred billion cubic meters in Yuanba area,Northeast Sichuan Basin. However,the characteristics and gas accumulation control factors are not clear. Based on cores,thin sections and physical properties,the characteristics and gas accumulation control factors of T3x3 were studied through correlation between well and seismic data. The results indicate that the dominant sedimentary facies are braided river delta plain and delta front. The calcarenaceous sandstones are characterized by high carbonate debris content and low quartz content,and low natural gamma value and high resistance. The calcarenaceous sandstones are of low porosity and extra-low permeability. The reservoirs have a variety of pore types,which are dominated by dissolution pores and authigenic mineral intercrystal pores,followed by micro-fractures. The dissolution pores mainly occur in between calcarenaceous grains and have good connectivity. They are the main pore paces of high-quality reservoirs. The prior factors of gas accumulation and high production are the existence of conglomeratic calcarenaceous sandstones,calcarenaceous sandstones and glutenites in distributary channels of delta plain and delta front. The horizontal and low-angle interlayer fractures and the dissolution pores along the fractures are the determinant factors for the gas accumulation. In addition,structures and faults are also important factors.