川东北地区长兴组台缘礁滩带沉积结构及储集层分布

Sedimentary Texture and Reservoir Distribution of Platform Margin Reef-Flat Zone in Changxing Formation of Northeastern Sichuan Basin

利用露头、钻井、分析化验及地震资料,对川东北地区晚二叠世长兴期开江—梁平陆棚东、西两侧及城口—鄂西海槽西侧发育的三排台缘带沉积结构与礁滩储集层进行对比,识别出迁移-加积型和加积型两种台缘带沉积结构。迁移-加积型台缘带发育有元坝—龙岗—兴隆场和镇巴—城口—利川两个台缘带,生物礁滩具有明显的横向陡缓相间结构,缓坡区台缘斜坡和礁滩迁移明显,分布广,陡坡区加积明显;加积型台缘带主要为铁厂河—普光—罗家寨台缘带,横向上存在地貌陡缓差异,台缘礁滩集中发育,迁移不明显。沉积期古地貌和海平面变化联合控制台缘礁滩发育及储集层总体分布,生物礁滩主要分布在高位体系域中—上部,白云岩储集层普遍发育于高位体系域晚期,且陡坡区白云岩厚度大。储集层的分布具有明显的垂向差异性和分段性,长一段加积型台缘带易于形成白云岩储集层,陡坡区白云岩化略强;长二段多排生物礁滩共存的迁移-加积型台缘带易于形成连片的白云岩储集层,而加积型台缘礁滩白云岩化带较窄。

Using the data of outcrop, drilling, laboratory analysis and seismic, the paper compares the sedimentary textures and reef-flat res-ervoirs of 3 sets of platform margin zones developed on the east and west sides of Kaijiang—Liangping continental shelf and the west sideof Chengkou—Exi trough during the Changxing Period of the Late Permian in the northeastern Sichuan basin, and identifies 2 sedimentarytextures of migration-aggradation type and aggradation type. The platform margin zone of migration-aggradation type mainly consists of 2 platform margin zones of Yuanba—Longgang—Xinglongchang and Zhenba—Chengkou—Lichuan, the biological reef flat has an obvioussteep-gentle alternating structure, the platform margin slope and reef flat in the gentle slope area are characterized by significantly migra-tion and wide distribution, and obvious aggradation occurs in the steep slope area. The platform margin zone of aggradation type is dominat-ed by the platform margin zone of Tiechanghe—Puguang—Luojiazhai, in which the geomorphology is different laterally, and platform mar-gin reef flats are developed concentratedly and have no obvious migration. Both the palaeogeomorphology and sea level changes during de-position controlled the development of platform margin reef flat and the overall reservoir distribution. Biological reef flat is mainly distribut-ed in the middle—upper parts of highstand system tract, dolomite reservoir was generally developed at the late HST period and the thick-ness of the dolomite reservoir in the steep slope area is larger than that in the gentle slope area. The reservoir distribution is featured withobvious vertical difference and segmentation. The dolomite reservoir tends to form in the platform margin zone of aggradation type in thefirst member of Changxing formation and slightly strong dolomitization is noted in the steep slope area. Contiguous dolomite reservoir tendsto form in the migration-aggradational platform margin zone in which multiple rows of biological reef flat co-exist in the second member ofChangxing formation, and relatively narrow dolomitized belts are distributed in the aggradational platform margin reef flat.