四川盆地西部龙门山地区中二叠统碳酸盐岩储层特征及勘探方向

Characteristics and exploration direction of the Middle Permian carbonate reservoirs in the Longmenshan mountain areas, western Sichuan Basin

四川盆地西部龙门山地区近年来相继在ST1井、LT1井中二叠统栖霞组—茅口组钻获高产工业气流,展现出良好的天然气勘探前景。为了进一步认识该区天然气聚集层系的储集性,基于大量的地面露头与钻井资料,采用宏观与微观相结合的方法,分析了该区栖霞组—茅口组的储层特征及其主控因素,并结合已开发气藏的特征,综合评价了有利的天然气勘探区带。研究结果表明:(1)龙门山北段前缘及南段前缘在中二叠世沉积期发育台地边缘滩微相,是有利于规模储集体发育的地区;(2)中二叠统储集体主要为缝洞—孔隙型与孔隙—缝洞型,前者常见于栖霞组,而后者则多见于茅口组;(3)控制中二叠统储层大规模发育的因素主要是沉积微相、白云石化作用、溶蚀作用及构造破裂,沉积微相是储层规模发育的基础,白云石化作用和溶蚀作用改善了储层的渗流能力,构造破裂则促进了大规模的溶蚀改造作用。结论认为:(1)龙门山北段中坝—双鱼石台缘滩区是最有利的天然气勘探区带;(2)龙门山南段莲花山—平落坝台缘滩区是次有利的勘探区带;(3)九龙山—老关庙、大邑—大兴场台内滩区是积极探索寻找大规模岩溶缝洞型气藏的有利区带。

In recent years, high-yield industrial gas flows have been obtained from the Permian Qixia-Maokou strata successively in Wells ST1 and LT1 in the Longmenshan mountain areas in the western Sichuan Basin, and a good gas exploration prospect is presented. To further understand the reservoir property of natural gas accumulation strata in this area, we analyzed the reservoir characteristics of Qixia and Maokou Fms in this area and their main control factors macroscopically and microscopically based on abundant surface out- crops and drilling data. Then, combined with the characteristics of developed gas reservoirs, favorable natural gas exploration zones were evaluated comprehensively. And the following research results were obtained. First, the microfacies of platform marginal banks are devel- oped in the front areas of northern section and southern sections of Longmenshan during the sedimentation of Middle Permian strata, so it is favorable for the development of scale reservoirs. Second, the Middle Permian reservoirs are mainly of fractured-vuggy-porous type and porous-fractured-vuggy type. The former is often occurred in the Qixia Fm while latter is mostly in the Maokou Fm. Third, scale development of Middle Permian reservoirs is mainly dominated by sedimentary microfacies, dolomitization, dissolution and structure fracturing. Among them, sedimentary microfacies are the foundation of scale reservoir development, dolomitization and dissolution improves the seepage capacity of reservoirs and structure fracturing promotes the scale reworking of dissolution. It is concluded that the Zhongba- Shuanyushi platform marginal bank area in the northern section of Longmenshan will be the most favorable gas exploration zone, the Lianhuashan-Pingluoba platform marginal bank area in the southern section of Longmenshan will be the secondary, and the Jiulongshan- Laoguanmiao and Dayi-Daxingchang intra-platform banks will be the favorable zones for the exploration of large karst fractured-vuggy gas reservoirs.