川东地区茅口组白云石化滩相储层特征及分布

Characteristics and distribution of dolomitized beach reservoirs in Maokou Formation,eastern Sichuan Basin

四川盆地中二叠统茅口组自20世纪50年代获得天然气发现以来,一直是油气勘探的热点层系。川中地区白云石化滩相储层无疑是近年来四川盆地茅口组勘探效果最好的领域,目前已逐步进入开发阶段。为了寻找茅口组下一个白云石化滩储层发育区,针对目前该层系勘探程度相对低的四川盆地东部地区进行了大量的老井复查以及地震资料解释,初步研究成果表明:①川东地区茅口组碳酸盐岩多相变为中二叠统孤峰段硅质岩,而在宣汉—万州一带硅质岩之下茅口组新发现白云石化滩相储层。②白云石化滩相储层镜下白云石以粉细晶结构为主,整体白云石化程度较高,纵向上主要发育在茅二段底部,测井孔隙度3.5%~4.3%,厚度普遍介于3~12 m,具备较好的储集性能。③储层平面分布预测结果显示,开江以东五百梯地区的储层厚度最大,局部超过15 m;川东硅质岩下茅口组白云石化滩相储层厚度大于6 m的勘探有利区域面积约3900 km2,有望开辟川东老区增储上产的新战场,成为潜在的接替领域。

The Middle Permian Maokou Formation has always been a hot spot in Sichuan Basin for oil and gas exploration since natural-gas discovery in the 1950s.With the increasing development,the dolomitized beach reservoirs of this formation in central ba-sin have been undoubtedly the most effective exploration target in recent years.So,large amount of reexamination on old wells and seismic-data interpretation were conducted for eastern basin with a little exploration in order to find out other areas with dolomitized reservoirs of the Maokou Formation.Results show that(i)carbonate rocks in the Maokou Formation,eastern Sichuan Basin,are most-ly transformed into siliceous rocks of the Gufeng Member,while dolomitized beach reservoirs have been newly found in the Maokou Formation beneath the siliceous rocks in Xuanhan-Wanxian area;(ii)microscopic observation displays the dolomitized reservoirs prin-cipally being fine to silty crystal dolomite with strong dolomitization.Vertically,the reservoirs are mainly developed at the bottom of Maokou 2 Member,with the logging porosity of 3.5%–4.3%and the thickness of 3–12 m,indicating better reservoir properties;and(iii)for them,the planar-distribution prediction implies the largest thickness in Wubaiti area to the east Kaijiang,over 15 m in some areas.And favorable exploration areas with the dolomitized beach reservoirs of Maokou Formation thicker than 6 m beneath siliceous rocks in eastern basin are approximately 3,900 km².These areas are expected to become new battlefields for increasing reserves and produc-tion in eastern Sichuan Basin.