冀中坳陷文安斜坡顺向及反向断层侧向封闭性差异分析

Differences of lateral sealing ability between consequent fault and antithetic fault in Wen'an slope

为揭示含油气盆地中断层对油气成藏与分布的控制作用,以冀中坳陷文安斜坡为研究靶区,从顺向及反向断层控制油气富集部位及规模的差异出发,综合滑入断裂带内围岩成分及断裂带内部结构的不对称性等特征,分析不同配置类型断层的泥质含量与风险断距的差异及其对侧向封闭性的控制作用。研究结果表明:(1)在地层沉积环境相近的情况下,断层断距小于单层砂泥岩厚度和断层断距为单层砂泥岩层厚度的奇数倍时,反向断层目的点的泥质成分明显高于顺向断层;断层断距为单层砂泥岩层厚度的偶数倍时,反向断层目的点的泥质成分与顺向断层相等;在文安斜坡沙一段内反向断层的断层岩泥质含量平均值较顺向断层高6%。(2)为封闭较厚的上盘破碎带,顺向断层形成封闭时所需的临界断距明显大于反向断层,文安斜坡顺向断层风险断距的平均值约为反向断层的1.8倍。(3)理论与实例分析共同证实,反向断层更容易形成侧向封闭,这与油气主要富集在反向断层附近相吻合,但在文安斜坡内断层断距约为单层砂泥岩层厚度的偶数倍,断层岩泥质含量近似相等。这可能是导致文安斜坡顺、反向断层封闭烃柱高度近于一致的主要原因。上述结论可为油气田勘探开发提供有利的指导。

To reveal the controlling effect of faults on hydrocarbon accumulation and distribution in petroliferous basin,taking the Wenan slope of Jizhong Depression as the target area.Based on the differences in hydrocarbon accumulation site and scale between consequent faults and antithetic faults,then combing the characteristics of the surrounding rock which slide into the fault zone and the asymmetry of the internal structure of the fault zone,finally analysis the differences between clay content(SGR),risk displacement and their effects on lateral sealing in different configuration types of faults.The result indicated that:(1)in the case of similar sedimentary environment,when the fault displacement is less than the thickness of single sand-mudstone layer and the fault displacement is odd times of the thickness of single sand-mudstone layer,the clay content of the target point of the antithetic fault is significantly higher than that of the consequent fault;when the fault displacement is even times of the thickness of the single sand-mudstone layer,the clay content of the target point of the antithetic fault is equal to that of the consequent fault.The clay content which sliding through the target point of antithetic fault is significantly more than that of the consequent fault,the average value of SGR of antithetic faults is 6%higher than that of consequent faults in Es1 layer of Wenan slope.(2)To seal the thicker damage zone in hanging wall,the critical displacement required for the consequent fault is significantly larger than that of the antithetic fault,and the average risk displacement of consequent fault is about 1.8 times as large as that of antithetic fault in Wenan slope.(3)Theoretical and case analysis confirmed that:the antithetic faults are more likely to form lateral seal,which is consistent with oil and gas mainly accumulated near the antithetic fault.However,in the Wenan slope,and the fault displacement is even times of the thickness of single sand-mudstone layer,so that the clay content of fault rock is approximately equal,which may be the main reason for the nearly consistent height of hydrocarbon columns sealed by both consequent and antithetic faults in the Wenan slope.The above conclusions can provide favorable guidance for the exploration and development of oil and gas fields.