乌石凹陷南陡坡带流二段源-汇系统及物性差异性分析

doi:10.19657/j.geoscience.1000-8527.2018.06.05

摘要/Abstract

摘要：

乌石凹陷南陡坡带流二段是近年北部湾盆地油气勘探的重要层系。为明确砂体及有利储层的分布规律,以钻井、地震、分析化验等资料为基础,逐一对流二段沉积体系源-汇系统各要素进行精细解剖,并结合断裂体系的分析,探讨了断裂-物源耦合控砂模式及有利储层分布主控因素。研究表明:区域性湖退促使了流二段中亚段扇三角洲体系的形成;F7断裂展布及活动特征控制了砂体的分布,总结建立了3种类型的断裂控砂模式,断坡带和断裂转换带控制了大-中型扇三角洲体系的发育;母岩类型的差异是储层溶蚀强弱不同的主要原因,中-西区母岩以磁铁矿型花岗岩为主,沉积物中含较多的钾长石等不稳定矿物,溶蚀孔发育,后期的溶蚀作用极大地改善了储层物性。综合以上分析,认为中-西区因大-中型扇三角洲体系发育且储层物性较好,是有利的勘探区域。

关键词: 乌石凹陷, 流二段, 源-汇系统, 沉积体系, 物性差异, 溶蚀作用

Abstract:

In recent years, the southern steep slope of the Wushi Sag has become an important oil-gas exploration target in the Beibuwan Basin, in which the second member of the Liushagang Formation is considered as the main target layer. To identify the distribution pattern of sand and favorable reservoirs, we conducted detailed source-to-sink and fracture system analyses, discussed the coupled fracture-provenance deposition controls and the main factors of favorable reservoir distribution, based on comprehensive analyses of drilling and seismic data. The results reveal an obvious lake retreat in the middle bed of the Liushagang Formation second member, which developed a fan delta system. The slope-break and F7 fault zone likely controlled the development of medium-large fan delta systems in this area, and we have summarized three types of structurally deposition control patterns. Parent lithologic differences are likely the main cause for the reservoir dissolution. The main parent rock type in the central and western districts is magnetite granite. Its sediments contain less stable minerals such as K-feldspar, which formed dissolved pores and improved the physical properties of the reservoir. The above analysis shows that the central and western districts are favorable exploration areas due to the large fan delta development and good reservoir physical properties.

Key words: Wushi Sag, the second member of Liushagang Formation, source-to-sink system, sedimentary system, reservoir property variation, dissolution

中图分类号:

TE122

何卫军, 徐万兴, 刘娟, 刘芳, 焦祥燕. 乌石凹陷南陡坡带流二段源-汇系统及物性差异性分析[J]. 现代地质, 2018, 32(06): 1161-1172.

HE Weijun, XU Wanxing, LIU Juan, LIU Fang, JIAO Xiangyan. Source-to-sink System and Reservoir Property Variation of the Second Member of Liushagang Formation in the Southern Steep Slope, Wushi Sag[J]. Geoscience, 2018, 32(06): 1161-1172.

图/表 10

图1 乌石凹陷构造纲要及构造单元

Fig.1 Structural outline and division of tectonic units at the Wushi Sag

图2 乌石凹陷F7断裂平面展布及其活动性分析

Fig.2 Distribution and activity analysis of F7 fault at the Wushi Sag

图3 研究区钻井重矿物组合、母岩类型及古水流方向特征

Fig.3 Characteristics of heavy mineral assemblages, parent-rock types and paleocurrent direction of drill holes in the study area

图4 流沙凸起北缘地震剖面(剖面位置见图1)

Fig.4 Seismic cross section of the northern margin of the Liusha Bulge (location shown in Fig.1)

图5 流二段扇三角洲粒度概率分布曲线(a)和C-M分布图(b)

Fig.5 Grain-size probability curves (a) and C-M diagram (b) of the fan delta of the Liushagang Formation second member

图6 W17-5b井钻井壁心及电阻率成像特征

Fig.6 Characteristics of sidewall core and resistivity imaging of well W17-5b

图7 乌石凹陷南陡坡带扇三角洲地震剖面(剖面位置见图1) (a)顺物源方向地震剖面;(b)垂直物源方向地震剖面

Fig.7 Seismic cross section of the fan delta in the southern steep slope, Wushi Sag (location shown in Fig.1)

图8 F7断裂发育样式及控砂模式

Fig.8 Development pattern and sand-controlling model of F7

图9 乌石凹陷南陡坡带流二段均方根振幅属性(RMS)和平面沉积相图

Fig.9 RMS amplitude and sedimentary facies map of the Liushagang Formation second member in the southern steep slope, Wushi Sag

图10 乌石凹陷南陡坡带流二段储层物性特征 (a)水下分流河道砂岩孔隙度与埋深关系;(b)水下分流河道砂岩渗透率与埋深关系;(c)沉积微相-孔隙度统计图;(d) 沉积微相-渗透率统计图;(e)W22-2井3 680 m样品砂岩铸体薄片镜下照片;(f)W17-6井3135.5m样品砂岩铸体薄片镜下照片;(g)砂岩分类三角图;(h)研究区分区图

Fig.10 Reservoir physical characteristics of the Liushagang Formation second member in the southern steep slope, Wushi Sag

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