川东南地区中—下寒武统膏岩层系分布特征及其影响因素

Distribution characteristics and influencing factors of Middle-Lower Cambrian gypsum in southeastern Sichuan Basin

川东南地区中—下寒武统龙王庙组和高台组为膏岩层系,石膏岩广泛发育,被认为是该区震旦系至中—下寒武统储层的盖层。通过统计钻井和二维地震资料,结合前人相关成果,研究膏岩层系的岩性、纵向发育和平面分布特征,分析构造挤压作用对石膏岩流动加厚和平面分布特征的影响。川东南地区中—下寒武统膏岩层系中与膏盐和含膏有关的岩性主要为石膏岩、白云质石膏岩、膏质白云岩与含膏白云岩,纵向上膏岩层系岩性组合和单层厚度变化较大,平面上石膏岩分布广,但累计厚度变化较大;在构造挤压作用下,川东南低陡构造带中—下寒武统石膏岩类常向背斜核部流动,造成石膏岩在背斜轴部明显加厚,揉皱和底辟等伴生构造发育;由于石膏岩的流动性,相应的膏岩层系厚度平面变化与低陡构造带的构造变形部位有相关性,沿低陡构造带的走向膏岩层系厚度在背斜部位一般加厚,在向斜部位减薄较明显。

The Middle-Lower Cambrian Longwangmiao Formation and Gaotai Formation in southeastern Sichuan Basin are gypsum rock layer systems,where gypsum rocks are widely developed and considered to be the Sinian to Middle-Lower Cambrian reservoir seals.Based on the drilling data and 2D seismic profile data,and combined with previous research results,this paper studies the lithologic features,vertical development and plane distribu⁃tion characteristics of the gypsum rock layer system and analyzes the influence of tectonic compression on the flow deformation and plane distribution characteristics of gypsum rock.The gypsum salt and gypsum bearing lithologies in the Middle-Lower Cambrian gypsum rock layer system in the study area mainly include gypsum rock and dolomitic gypsum rock,as well as gypsiferous dolomite and dolomite with gypsum.The lithologic association and single layer thickness of the gypsum rock layer system vary greatly vertically.The gypsum rocks are widely distributed in the plane,but the accumulated thickness changes greatly.Under tectonic compression,the Middle-Lower Cambrian gypsum rocks in the low⁃steep folds in the southeastern Sichuan Basin usually flowed into the core of the anticline and obviously thickened.Crumpled,diapir and other associated structures developed.Due to the fluidity of gypsum rock,the plane variation of gypsum rock thickness is related to the structural deformation position of the low⁃folds,which is generally thickened in the anticline along the strike of the low⁃steep folds and obviously thinned in the syncline.