致密砂岩气藏孔隙分形特征与动态水锁损害关系研究

Research on the Relationship between Pore Fractal Characteristics and Dynamic Water Lock Damage in Tight Sandstone Gas Reservoirs

摘要: 鄂尔多斯盆地南部某区块的致密砂岩气藏，其上古生界石盒子组地层孔渗低、泥质含量高、孔喉半径小导致水锁伤害严重，严重制约其气藏开发效率。因此，本文以鄂南某区块盒一段致密砂岩为对象，结合低场核磁共振(NMR)及分形理论，系统表征孔隙结构非均质性，揭示孔隙结构特征与水锁伤害的关系。结果表明，研究区块岩心的整体平均分形维数为2.354，小孔段不具备分形特征，中孔与大孔的平均分形维数分别为2.546、2.799，且与水锁损害率呈显著正相关，其孔隙结构复杂性通过增强毛细管力与液相滞留主导水锁效应。本研究提出以中孔分形维数为主要的致密砂岩气藏的水锁风险主要评价指标，为致密砂岩气藏高效开发提供理论支撑。

Abstract: In the tight sandstone gas reservoir of a certain block in the southern part of the Ordos Basin, the Upper Paleozoic Shihezi Formation has low porosity and permeability, high clay content and small pore throat radius, which leads to severe water lock damage and seriously restricts the development efficiency of the gas reservoir. Therefore, this paper takes the tight sandstone of the Boxi 1st Member in a certain block in the southern Ordos Basin as the object, optimizes the efficient water lock release agent, and combines low-field nuclear magnetic resonance (NMR) and fractal theory to systematically characterize the heterogeneity of pore structure and reveal the relationship between pore structure characteristics and water lock damage. The results show that the overall average fractal dimension of the core in the study block is 2.354. The small pore segment does not have fractal characteristics, and the average fractal dimensions of the medium and large pores are 2.546 and 2.799, respectively, and are significantly positively correlated with the water lock damage rate. The complexity of the pore structure enhances the capillary force and liquid phase retention, which dominates the water lock effect. This study proposes the average fractal dimension of medium pores as the main evaluation index of water lock risk in tight sandstone gas reservoirs, providing theoretical support for the efficient development of tight sandstone gas reservoirs.