基于“伞式解构方法”的致密储层微观非均质性综合量化表征研究

As an important type of unconventional resources, tight oil and gas reservoirs are characterized by quasi-continuous reservoir formation, small pore-throat scale and obvious micro-heterogeneity. At present, there are still major theoretical challenges and vast potential for exploration in substantially improving the recovery rate of resources. Based on the traditional reservoir theory and experimental methods, and through the thorough cross-cutting of the relevant theories of computer mathematics and physics, this paper intends to put forward the comprehensive characterization and evaluation system for the micro-heterogeneity with the core method named “Umbrella Deconstruction Method” which is suitable for tight reservoir, then construct the new model for the dynamic segmentation and characterization on pore and throat, finally explore the complete distribution characteristics of pore-throat in tight reservoirs so as to evaluate the heterogeneity of pore-throat development on a continuous scale. The applicant has preliminarily put forward the idea of "Umbrella deconstruction" in which " direct multi-directional dissection" of rock samples was used instead of "indirect multi-directional cutting" of CT data, which can lay a solid foundation for the further accurate identification of minerals and pore-throat in tight reservoirs so as to form the systematic characterization and evaluation system of "Umbrella Deconstruction method". The research achievements would provide important theoretical support and practical basis for revealing the storage-seepage mechanism of tight reservoir and the distribution rule of “dessert”, and guiding the effective development of tight oil and gas.

致密油气储层作为非常规资源的重要类型，具有准连续-连续型成藏，孔喉尺度小，微观非均质性强等显著特征。目前在大幅提高资源动用率方面仍面临重大理论挑战，探索潜力广阔。本课题紧密着眼致密储层孔喉-矿物量化表征评价的核心科学问题，在传统储层理论与实验方法基础上，通过深入交叉计算机数理学科相关理论，拟提出以“伞式解构方法”为核心，适宜于致密储层的微观非均质性综合表征评价体系，构建得到致密储层孔隙-喉道动态判识表征新模型，探索致密储层孔隙-喉道全信息分布特征并开展连续尺度孔隙-喉道发育的非均质性评价。申请人已通过前期探索初步提出以岩石样品“多向直接解剖”代替CT数据体“间接多向切割”的“伞式解构”理念，可为本课题中深入开展致密储层矿物、孔喉准确识别，形成系统的“伞式解构方法”表征评价体系奠定坚实基础。研究成果可为揭示致密储层储渗机理及“甜点”分布规律，指导致密油气有效开发提供重要的理论支撑与实践依据。

致密储层微观非均质性的综合量化表征是探索剩余油气分布机理的重要途径，具有显著的科学及工程实践价值。现有技术在孔隙结构表征方面尚无法完全实现样本尺寸与观测分辨率的兼顾。前人为了尽可能提高分辨率从而捕捉储集空间发育细节，不得不钻取较小尺寸样品开展实验，如此将不可避免地引起样品代表性不佳，结论有失偏颇。本项目从已开展的“伞式解构”的预实验入手，通过深入完善“伞式解构”的具体细节和应用对象，对致密储层孔隙、裂缝、矿物(元素)微观非均质性和各向异性开展了全方位的量化表征评价，并在此基础上开展了致密型储层动静态属性演化的拓展性研究。全方位解析了鄂尔多斯盆地致密油储层的微观各向异性，发现八向切片的分形维数与孔隙率、渗透率和单位面积孔喉数量均呈现良好线性相关。分形维数不仅表征孔喉复杂程度，亦可指示孔隙率、渗透率和孔喉的发育概率。通过开展延长组长7段页岩元素分布测试发现，八个角度的元素分布类型各异，是宏观尺度存在优势断裂方向的关键矿物学证据。通过定义“孔喉强度”的关键参数，结合计算几何理论，构建了孔喉动态判识表征新模型。验证结果表明， “最大球法”得到的孔-喉分割结果与上述新模型得到的结果相比，孔隙与喉道的分布总体符合度较高且趋势相对一致，同时恰恰体现出新模型在突出较小尺度孔隙与较大尺度喉道方面的显著优势。研究认为，不同实验由于检测及数据分析原理的差异，对同一储层的表征结果必然存在差异。实际应用中，应结合多种测试结果综合分析。回归地质原理本身，从与多类型矿物与孔喉分布的关系切入，结合概率统计理论，构建得到了致密储层全孔隙-喉道分布曲线。全孔隙-喉道分布曲线表明，虽然孔隙由喉道连接，但孔隙和喉道对油气储集和渗流的贡献率不同。许多情况下，大孔隙不一定与大喉道匹配，纳米级喉道是评估致密储层流动能力的关键因素。本项目成果为致密/页岩油气的甜点识别与提高采收率提供了重要理论与实践依据。