川西北地区中二叠统茅口组沉积演化及其对岩溶储层发育的控制

Sedimentary evolution and its influence on karst reservoir development of the Middle Permian Maokou Formation in the northwestern Sichuan Basin,China

四川盆地西北部(川西北)地区中二叠统茅口组以灰岩储层为主,在局部地区取得了较好的天然气勘探效果。由于钻井资料的短缺,对川西北茅口组沉积相分布及演化缺乏明确认识,导致对储层发育控制因素认识不足,并影响了后续的油气勘探。为阐明茅口组储层的发育规律,利用钻测井及地震资料,通过将宏观与微观研究相结合,分析了茅口组沉积岩石的岩石类型及分布,探讨了有利沉积相分布及其对有利储层的控制。研究表明:川西北部地区茅一段—茅二段沉积时期,西部中坝—双鱼石地区发育台地边缘生屑滩沉积,其他地区以开阔台地灰质潟湖沉积为主,东侧九龙山地区发育台内生屑滩。茅三段沉积时期沉积格局发生较大变化,矿山梁—九龙山一带的相对海平面升高,发育盆地—斜坡相的硅质岩,并首次确定了该硅质岩为生物化学沉积。研究阐明了川西北地区中二叠统茅口组沉积格局的变化,提出双鱼石地区和九龙山地区茅口组沉积相分布及岩性的差异影响了二者的颗粒滩储层及岩溶储层的发育模式,为有利储层的勘探提供了地质依据。

The Middle Permian Maokou Formation in northwest Sichuan Basin is mainly composed of limestone,which is deeply buried and has poor physical properties.It is a kind of low porosity and low permeability reservoir,with some good area of natural gas exploration.In order to clarify the sedimentary characteristics of the ultra-deep reservoir of the Maokou Formation,this paper analyzes the reservoir rock lithology types and its distribution,sedimentary facies and its controlling to the favorable reservoir by using drilling,logging and seismic data,and further discusses the controlling factors on high-quality reservoir development.The results show that during the first and the second members of Maokou Formation in Northwest Sichuan,bioclastic beach of the platform margin was developed in the Zhongba-Shuangyushi areas,and open platform in the other areas.The bioclastic beach of open platform was developed in the Jiulongshan area.The sedimentary pattern changed greatly during the third member of Maokou Formation,the relative sea level raised in Kuangshanliang-Jiulongshan areas,and developed the basin-slope facies with silicalite of biochemical origin.So,there was a new platform margin which was formed in the area from Shuangyushi to Jiange.This study found the change of sedimentary pattern of the Middle Permian Maokou Formation in the northwestern Sichuan Basin,and it is found that the differences of sedimentary facies and lithology of the Maokou Formation in Shuangyushi area and Jiulongshan area affected the karstification mode of those two areas,which can guide the exploration of favorable reservoirs.