滇东-黔西二叠系龙潭组层序格架内致密天然气储层特征

Characteristics of tight gas reservoir in sequence framework of Permian Longtan Formation in eastern Yunnan-western Guizhou area,China

在沉积序列、沉积特征和物性分析基础上,研究滇东-黔西地区二叠系龙潭组层序格架和致密储层类型及其空间展布规律。龙潭组是扬子板块在二叠纪碳酸盐台地基础上形成的以煤系为特点的海陆过渡相沉积,主要物源区是西部川滇地区,相带走向为北东-南西向。滇东-黔西一带靠物源一侧的西部地区以河流相细砂岩为主,往东为以含煤层系为特点的中间过渡相带和靠海一侧的河口湾海岸相带。龙潭组岩石类型主要有煤岩、泥页岩和致密砂岩,这3种岩石构成了3种致密天然气储层,都具有一定的含气性,但含气量从煤岩→泥页岩→致密砂岩具有逐渐变弱的变化规律。煤岩物性相对较好,泥页岩物性较差,致密砂岩物性最差。煤岩储层在黔西的大方-金沙-六盘水地区和滇东的富源-曲靖-罗平-丘北地区较为发育,三角洲平原、潮坪-潟湖相是煤层气发育的有利相带;往东南靠海方向主要发育泥页岩致密储层的潮坪-潟湖相带;致密砂岩储层主要发育在北西方向靠物源一侧的三角洲前缘亚相。煤岩和泥页岩在相邻的黔北地区、四川泸州、重庆永川和云南的弥勒、普者黑等地延展分布,这些区域的龙潭组可能存在相应的致密储层和天然气藏。

The Longtan Formation coal series is a set of transitional facies deposits formed on the Permian carbonate platform in the Yangtze plate.West Sichuan-Yunnan area is the main provenance of Longtan Formation and the facies zone is in a northeast-southwest direction.Based on the analysis of sedimentary sequence,sedimentary characteristics and physical properties,the sequence framework and tight reservoir types of Permian Longtan Formation in the eastern Yunnan-western Guizhou area are studied.The study shows that the fluvial facies fine sandstone is dominant in the western part of the provenance area,and the intermediate transitional facies is characterized by coal seam system and the estuarine coastal facies is dominant in the eastern Yunnan-western Guizhou area.The main rock types of Longtan Formation are coal rock,mud shale and tight sandstone,which constitute three kinds of tight gas reservoirs with certain gas content.However,the gas content changes gradually from coal rock to mud shale to tight sandstone.Comparatively,the physical properties of coal are relatively good,mud shale is poor,and tight sandstone is the worst.The coal reservoirs are well developed in Dafang-Jinsha-Liupanshui area in western Guizhou and Fuyuan-Qujing-Luoping-Qiubei area in eastern Yunnan.The delta plain,tidal flat and lagoons are favorable facies zones for coal bed methane(CBM)development,and the latter two facies of shale tight reservoir are mainly developed in the direction of southeast to the sea,while the tight sandstone reservoirs are mainly developed in the delta front subfacies on the northwest side of provenance.Coal rock and mud shale are distributed in the northern Guizhou,Luzhou of Sichuan Province,Yongchuan of Chongqing,and Mile and Puzhehei of Yunnan Province.It is likely that Longtan Formation in these areas may have corresponding tight reservoirs and gas reservoirs.