四川盆地须家河组一、三、五段天然气勘探潜力分析

四川盆地上三叠统须家河组一、三、五段主要作为须二、须四、须六段的烃源层，勘探上一直未引起足够的重视，勘探程度低，但近期钻井揭示此3段有频繁的气显示，部分井测试获工业气流。为此，从地层特征、沉积相特征、储层特征、运聚条件等方面，分析了须家河组一、三、五段的含油气地质条件及勘探潜力。结果表明：①须家河组一、三、五段有利沉积相带主要分布在盆地周缘靠物源区，发育三角洲前缘水下分流河道、河口坝及席状砂沉积微相，盆内砂体局部富集，具备形成储层的物质基础；②这3个层段也发育储层，总体上表现为低孔隙度、低渗透率致密砂岩储层特征，但局部地区发育相对高孔隙度储层（如中坝地区须三段，孔隙度最大值达13％），有利储层发育区主要分布在川西及川中西部地区，储层厚度最大达30 m；③须家河组一、三、五段发育自生自储型气藏，总生气量达258.23×10¹² m³，资源潜力大，运聚条件较好，具备较好的天然气成藏潜力，由此突破了须一、须三、须五段主要作为烃源层的传统认识。结论认为：该区须家河组一、三、五段具备较好的天然气勘探潜力，有利勘探区块主要分布在川西北、川西南及川中西部地区。

Gas exploration potential of the 1st, 3rd and 5th members of Xujiahe Fm reservoirs in the Sichuan Basin

Since the 1^st, 3^rd and 5^th members of Upper Triassic Xujiahe Fm in the Sichuan Basin were previously regarded as the major source rocks of the reservoirs in the 2^nd, 4^th and 6^th members of Xujiahe Fm, petroleum exploration in these source rock intervals has not attracted much attention, leading to a low level of exploration maturity. However, recent drilling reveals rich gas shows in these 3 intervals and industrial gas flows are obtained in some wells. This paper analyzed the exploration potential of these three source rock intervals in the respect of their stratigraphic features, sedimentary facies and hydrocarbon migration and accumulation conditions. The following conclusions are obtained. (1) The favorable sedimentary facies belts of these source rock intervals mainly occur in the marginal area of this basin adjacent to the provenance where sedimentary microfacies such as delta front underwater distributary channel, mouth bar and sheet sands are developed. (2) These 3 members also contain tight sand reservoirs with low porosity and permeability, but with some areas having relatively high porosity, such as the 3^rd member of Xujiahe Fm in the Zhongba area with a maximum porosity up to 13%. The favorable reservoirs are mainly distributed in the west and the western Middle Sichuan Basin where the maximum thickness of reservoirs is up to 30 m. (3) Indigenous gas reservoirs are developed in these 3 source rock intervals with a total generated gas volume of 258.23 trillion m³. The resource potential is large and the migration and accumulation conditions are favorable. Therefore, the 1^st, 3^rd and 5^th members of Xujiahe Fm have a fairly good gas exploration potential, and the play fairways are mainly distributed in the northwestern, southwestern and western middle parts of the Sichuan Basin.