鄂尔多斯盆地西南缘镇泾地区断缝体发育特征及油气富集规律

2022年 43卷 第No.6期
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Fault-fracture body growth and hydrocarbon enrichment of the Zhenjing area, the southwestern margin of the Ordos Basin
杨桂林 任战利 何发岐 张园园 王宝江 祁凯
Guilin Yang Zhanli Ren Faqi He Yuanyuan Zhang Baojiang Wang Kai Qi
断裂、裂缝对油气成藏有重要控制作用,镇泾区块位于鄂尔多斯盆地西南部不同构造单元交汇部位,受周缘强烈构造运动影响,断裂、裂缝普遍发育。在三维地震资料全覆盖的镇泾区块断裂、裂缝精细解释的基础上,对镇泾地区由断裂、伴生脆性破碎带及被其改造过的致密低渗砂岩共同构成的储集体——“断缝体”组合样式、形成期次、断缝体特征等分别进行了深入研究。断缝体主要发育5种构造组合样式,剖面上构造样式有堑垒式、阶梯式、地堑式、花状和紧闭平移式,分别对应于平面上的帚状、雁列式、平行直线式、拉分地堑式和直线式,不同组合样式具有不同的应力背景。通过地震解释和C-O同位素分析技术认为研究区断缝体带内主要存在3期断裂构造:印支期、燕山期和喜马拉雅期。其中燕山期是最主要也是最关键的断缝形成期,喜马拉雅期和印支期断裂活动相对较弱。利用K-Ar同位素、包裹体测温及热演化史分析等手段,明确了研究区三叠系延长组8段(长8段)断缝体油藏的成藏期为早白垩世中晚期。在断缝体三维刻画的基础上,结合断缝形成期与油气成藏的空间配置关系,对研究区长8段不同组合样式控藏机制进行了分析。研究结果表明雁列-阶梯式组合样式最有利于油气富集,其次是拉分地堑-花状、帚状-堑垒式组合样式,平行直线-地堑式和直线-紧闭平移式组合样式中油气富集程度最差。
Faults and fractures play a key role in hydrocarbon accumulation. The Zhenjing area has been taken as study subject as it contains numerous faults and fractures resulted from intensive tectonic movements due to its location at the intersection of different tectonic units in the southwestern Ordos Basin. Based on the fine interpretation of faults and fractures in the Zhenjing area fully covered by 3D seismic acreage, this paper makes an deep study on the combination style, formation period and characteristics of fault-fracture bodies composed of faults and associated brittle fracture zone as well as the modified tight (with low permeability) sandstone. There are mainly five structural combination styles of fault-fracture bodies. On a sectional view, including graben horst, ladder, graben, flower and tight translation types, corresponding respectively to broom, en echelon, parallel straight-line, pull-apart graben and straight-line combinations on a plane view. Different combination styles have different stress background. Through seismic interpretation and C-O isotope analysis, it is suggested that there are mainly three stages of tectonic activities in the fault-fracture body belt in the study area: Indosinian, Yanshanian and Himalayan periods. The Yanshanian period is the most important period for the formation of fractures, while the Himalayan and Indosinian periods are less important. By means of K?Ar isotope analysis, temperature measurement of inclusions and thermal evolution history analysis, it is clear that the hydrocarbon accumulation in fault-fracture bodies in Chang 8 member of the Yanchang Formation occurred mainly in the middle and late of Early Cretaceous. The three-dimensional description of fault-fracture bodies was combined with the determination of temporal relationship between the formation period of the fault-fracture and the hydrocarbon accumulation to analyze the reservoir control mechanism of different combination styles of the Chang 8 member in the study area. The results show that the en echelon ladder is the most favorable to hydrocarbon enrichment, followed by the pull-apart flower-shaped graben and broom-like graben horst, and the parallel straight-line graben and straight-line tight translation style are the least favorable to hydrocarbon enrichment.
油气富集; 断缝体; 延长组; 镇泾地区; 鄂尔多斯盆地;
hydrocarbon enrichment; fault-fracture body; Yanchang Formation; Zhenjing area; Ordos Basin;
10.11743/ogg20220609