构造抬升区泥页岩脆性破裂泄压特征及对页岩油富集的影响——以延安地区延长组长7亚段为例

Characteristics of pressure relief induced by shale brittle fracture in tectonic uplift area and its influence on shale oil enrichment: a case study of Chang 7 sub-member of Yanchang Formation in Yan'an area

张凤奇 孙越 刘思瑶 李艳霞 孙建博 王凤琴 刘刚 陈红果

ZHANG Fengqi SUN Yue LIU Siyao LI Yanxia SUN Jianbo WANG Fengqin LIU Gang CHEN Hongguo

西安石油大学 地球科学与工程学院, 西安 710065 西安石油大学 陕西省油气成藏地质学重点实验室, 西安 710065 陕西延长石油(集团)有限责任公司 研究院, 西安 710075

School of Earth Sciences and Engineering, Xi'an Shiyou University, Xi'an, Shaanxi 710065, China Shaanxi Key Laboratory of Petroleum Accumulation Geology, Xi'an Shiyou University, Xi'an, Shaanxi 710065, China Research Institute of Shaanxi Yanchang Petroleum (Group) Co., Ltd., Xi'an, Shaanxi 710075, China

为深入认识大幅度构造抬升引起的泥页岩脆性破裂泄压特征及对页岩油富集的影响，以鄂尔多斯盆地延安地区延长组长73亚段为研究对象，运用改进的超压判识图版和数值模拟技术，综合考虑构造抬升过程中温度降低、孔隙回弹、超压泥页岩脆性破裂泄压等作用，定量分析了研究区目的层不同岩性地层由异常高压转变为异常低压或近常压的演化过程，进一步总结了其对页岩油富集的影响规律。研究区长73亚段早白垩世末期超压成因主要为生烃作用和欠压实作用，砂岩层超压主要来源于邻近烃源岩的超压传递；晚白垩世以来构造抬升引起的孔隙回弹和温度降低主导了研究区长73亚段砂岩异常低压的形成，脆性破裂泄压和温度降低使得长73亚段泥页岩形成弱超压或近常压。研究区长73亚段顶底两套富有机质泥页岩脆性破裂泄压时间不同步，使得顶、底2套富有机质泥页岩与其夹持的砂岩间具有较大的油气运移动力(源储过剩压力差)，其大小为16~22 MPa；同时，油气保存过程中裂缝已闭合的顶部泥页岩封盖层仍与其下覆砂岩保持着约1.42~6.80 MPa的过剩压力差，一定程度上加强了页岩层系油气的封闭能力，不同源储配置下地层压力的差异演化对页岩油的富集起到了重要控制作用。

In order to gain a deeper understanding of the pressure relief characteristics of shale brittle fracture caused by large-scale tectonic uplift and its impact on shale oil enrichment, this paper, taking the Chang 73 sub-member of Yanchang Formation in Yan'an area of Ordos Basin as the research object, quantitatively analyzes the evolution of different lithological properties from overpressure to underpressure or near normal pressure, and further summarizes its influence on the enrichment of shale oil by utilizing the modified overpressure identification plate and numerical simulation techniques and taking into account the effects of temperature reduction, elastic rebound, and brittle rupture of overpressured shale in the process of tectonic uplift. The results show that the origins of overpressure at the end of the Early Cretaceous in the Chang 73 sub-member in the study area are mainly hydrocarbon generation and disequilibrium compaction, and the overpressure of the sandstone layer mainly originates from the overpressure transference from the neighboring source rocks; elastic rebound and temperature reduction due to tectonic uplift since the Late Cretaceous dominates the formation of underpressure in the Chang 73 sub-member sandstones in the study area, and brittle fracture pressure relief and temperature reduction lead to the formation of weak overpressure or near normal pressure in the Chang 73 sub-member shale. The timing of brittle fracture pressure relief of the top and bottom sets of organic-rich shale in the Chang 73 sub-member of the study area is not synchronized, resulting in large transport dynamics (source-reservoir excess pressure difference) between the top and bottom sets of organic-rich shale and their intercalated sandstones with magnitudes ranging from 16 to 22 MPa. Meanwhile, fractures in the top shale have closed during oil and gas preservation, and there is an excess pressure differential of about 1.42-6.80 MPa between it and the underlying sandstone, which strengthens the hydrocarbon containment capacity of the shale. Differential evolution of formation pressure under different source-reservoir configurations plays an important role in controlling shale oil enrichment.

国家自然科学基金 42172164;国家科技重大专项 2017ZX05039-001;西安石油大学创新与实践能力培养计划 YCS22214209

https://doi.org/10.11781/sysydz202305936