川北地区下寒武统龙王庙组混积特征及其对储层的影响

Characteristics of mixed sediments and influence on reservoir of Lower Cambrian Longwangmiao Formation, northern Sichuan Basin

王瀚 李智武 刘树根 宋金民 冉波 叶玥豪 韩雨樾 姜巽

WANG Han LI Zhiwu LIU Shugen SONG Jinmin RAN Bo YE Yuehao HAN Yuyue JIANG Xun

成都理工大学 油气成藏地质及开发工程国家重点实验室, 成都 610059

State Key Laboratory of Oil and Gas Reservoir Geology and Exploration, Chengdu University of Technology, Chengdu, Sichuan 610059, China

通过露头观察及室内薄片鉴定，将川北地区下寒武统龙王庙组混合沉积分为潮坪相相缘Ⅰ型、滩间海相相缘Ⅱ型、颗粒滩相相缘Ⅲ型及开阔海相事件Ⅰ型、开阔海相事件Ⅱ型混积。混积作用最强的潮坪相相缘Ⅰ型主要分布于龙王庙组底部、中部和顶部；而横向上，相缘型混积主要分布于西侧靠近陆源区的内缓坡地区，事件型混积主要分布于东侧远离陆源区的中（外）缓坡地区。川北龙王庙组整体表现为混积作用背景下北西—南东向碳酸盐岩缓坡沉积。混合沉积不利于颗粒滩的原始沉积，且较强混积作用减弱颗粒白云石之间的胶结作用，使得颗粒间抗压实效应降低，不利于原始孔隙的形成和保存；同时，石英稳定性较强，在酸性环境下难以发生溶蚀作用，降低了成岩中—晚期有机酸对储层的改善效果。川北地区龙王庙组不具备发育大规模颗粒滩叠加溶蚀型优质储层的地质条件。

Through outcrop observation and thin section identification, the mixed sediments of the Lower Cambrian Longwangmiao Formation in the northern Sichuan Basin are divided into tidal flat facies margin Ⅰ type, intershoal sea facies margin Ⅱ type, shoal facies margin Ⅲ type, open marine punctuated Ⅰ type and open marine punctuated Ⅱ type. The tidal flat facies marginⅠ type with the strongest mixing effect is mainly distributed in the bottom, middle and top of the Longwangmiao Formation. Laterally, the facies mixing sedimentation mainly distributes in the inner ramp which is close to the provenance on the west side, while the punctuated mixing sedimentation mainly distributes in the middle-outer ramp which is far away from the provenance on the east side. The Longwangmiao Formation in northern Sichuan Basin is characterized by NW-SE direction ramp sedimentation under a mixed sedimentation background. The mixed sedimentation is not conducive for the formation of a granular beach. The strong mixed deposits weakened the cementation between grain dolomites, leading to poorer compaction resistance, which is unfavorable for the formation and preservation of primary pores. Meanwhile, quartz has better stability and is difficult to dissolve in an acidic environment, which reduces the reservoir improvement by organic acids during the middle and late diagenetic stages. Therefore, the Lower Cambrian Longwangmiao Formation in northern Sichuan Basin does not have a lot of advantages to form high quality reservoir which is dominated by shoal deposits with obvious dissolution.

“十三五”国家科技重大专项（2017ZX05005003-007）和国家重点基础研究发展计划（973计划）项目（2012CB214805）联合资助。

https://doi.org/10.11781/sysydz201905663