摘要： 中二叠世末期,海水退出四川盆地,元坝地区茅口组上部灰岩普遍可见暴露、岩溶现象,但岩溶带的发育特征及其分布规律尚不明确。基于井-震联合解释的思路,通过岩心观察、测井岩性解释、三维地震数据体的层位标定与地震相解译等,特别是通过相对声波阻抗转换、地震地层切片分析等技术手段提高了地震数据的解释分辨率,建立了茅口组的层序地层格架,进而描述茅口组的沉积与岩溶特征,预测岩溶带的分布规律及模式。结果表明: (1)元坝地区茅口组共发育3个三级海侵—海退层序,生屑滩发育于第2个和第3个三级层序的海退旋回内,其中前者是在沉积古地貌高部位发育台内生屑滩,后者是在YB7井一带的台地边缘坡折带发育台缘生屑滩; (2)岩溶带的发育和分布受生屑滩控制,在岩心尺度主要表现为地表岩溶带、垂直渗流带、深部缓流带的高角度溶缝和溶洞、水平潜流带的顺层溶洞; (3)平面上,岩溶带集中发育在生屑滩内部靠近海岸的一侧,发育模式具有海岸型岩溶的特点; (4)水平潜流带顶部发育的顺层溶洞为茅口组岩溶带主要的储集空间,但大多已在表生期被火山凝灰质和灰岩碎屑等流水搬运物质和方解石等化学沉淀物质充填,现今储集能力总体较差。在此基础上,提出了元坝地区茅口组岩溶带的分布模式,并对其油气勘探意义与风险进行了讨论。

关键词: 井-震联合研究, 生屑滩, 顺层溶洞, 相控岩溶, 海岸型岩溶

Abstract: The upper part of the Maokou limestones in the Yuanba area of the Sichuan Basin suffered from karstic modification during the regional regression stage at the end of the middle Permian. However,the development characteristics and distribution pattern of the karst zone are ambiguous. This paper combined core observations,well-logging lithology interpretation,horizon calibration of three-dimensional seismic data volume and seismic facies interpretation. Relative acoustic impedance inversion and seismic slice image analysis techniques can increase the interpretation resolution of the seismic data. All these data were used to establish the sequence framework,and the sedimentary facies and karst distribution were illustrated to predict the distribution pattern and mode of karst zones. The results show that(1)three third transgression-regression(T-R)sequences were developed in the Maokou Formation of the Yuanba area. The bioclastic shoals were developed in the regression cycles of the second and the third tertiary sequences. In the second sequence,the inner-platform shoals were located at the topograghic high position. Meanwhile,in the third sequence,the platform edge debris beach was developed along the margin of the platform around well YB7. (2)The development and distribution of karst zones were dominated by bioclastic shoals,which presented vertically as a surface karst zone,vertical seepage zone,high-angle dissolution fracture and cave of the deep slow flow zone,and layer-parallel caves in the phreatic zone at the core scale. (3)The karst zones are located along the coastline side of the bioclastic shoals on the plane,presenting the coastal karst development mode. (4)The layer-parallel caves at the top of the phreatic zone were the major reservoir space of the karst zone in the Maokou Formation. However,the caves were mostly occupied by sediments(mainly tuffs and limestone silts)and cements(mainly calcites)in the meteoric diagenetic realm,remaining relatively limited reserve capacity at present. The karst distribution pattern of the Maokou Formation in the Yuanba area was proposed,and its impacts on hydrocarbon exploration and risks were also discussed.

Key words: well-seismic combined study, bioclastic shoal, parallel cave, facies-dominated karst, coastal karst

中图分类号: 

• P618.130.2+1