致密砂岩储层孔隙结构分形特征对气水渗流规律的影响——以苏里格气田东南部桃2区块山1段为例

Influence of pore structure fractal features of tight sandstone reservoir on gas-water seepage law: a case study of Shan 1 Member in Tao 2 block of southeastern Sulige Gas Field

李昊远 庞强 魏克颖 曾源 崔宇翔 朱玉双

西北大学大陆动力学国家重点实验室，陕西 西安 710069 西北大学地质学系，陕西 西安 710069 中国石油长庆油田分公司第三采气厂，内蒙古 鄂尔多斯 017300 中国石油长庆油田分公司第二采气厂，陕西 榆林 718100

State Key Laboratory of Continental Dynamics, Northwest University, Xi′an 710069, China Department of Geology, Northwest University, Xi′an 710069, China； 3.No. 3 Gas Production Plant, Changqing Oilfield Company, PetroChina, Ordos 017300, China   No. 2 Oil Production Plant, Changqing Oilfield Company, PetroChina, Yulin 718100, China

为了研究致密砂岩储层孔隙结构分形特征对气水渗流规律的影响，选取苏里格气田东南部桃2区块山1段8块岩心样品，利用铸体薄片、高压压汞、恒速压汞、气水相渗与真实砂岩模型气水驱替等实验,对不同半径的孔隙结构分形特征与气水渗流特征进行研究。结果表明：山1段储层发育的孔隙类型为残余粒间孔、长石溶孔、岩屑溶孔与晶间孔，喉道类型为缩颈状、片状、弯片状及管束状。采用高压压汞与恒速压汞实验对孔隙结构联合表征，依据样品物性、退汞效率、排驱压力及分选系数等参数，将储层样品划分为Ⅰ类与Ⅱ类。借鉴Hartmann等对孔隙的分类标准，将孔隙分为大孔（半径大于2.5 μm）、中孔（半径0.1~2.5 μm）和微孔（半径小于0.1 μm）。根据分形理论，研究区不同半径孔隙的平均分形维数均在2.2~2.8，大孔的分形维数与渗透率贡献值呈现明显的负相关性，中孔、微孔与渗透率贡献值的相关性弱。气水相渗实验结果表明，研究区样品束缚水饱和度较大，Ⅰ类储层的共渗区明显大于Ⅱ类储层。真实砂岩模型气水驱替实验的驱替形态与不同孔隙类型及其平均分形维数有对应关系。Ⅰ类储层为均匀驱替，Ⅱ类储层为网状驱替和指状驱替。因此，大孔分布频率高及分形维数较低的Ⅰ类储层为致密气藏勘探与开发的主要目标。

In order to study the influence of pore structure fractal features of tight sandstone reservoir on gas-water seepage law, eight core samples from Shan 1 Member of Shanxi Formation in Tao 2 block, southeast of Sulige Gas Field were selected to study the pore fractal features and gas-water seepage characteristics under different pore diameters by using casting thin section, high-pressure mercury injection, constant-speed mercury injection, gas-water relative permeability and real sandstone model gas-water displacement experiments. The results show that the types of pores developed in the Shan 1 Member are residual intergranular pore, feldspar dissolution pore, lithic dissolution pore and intercrystalline pore, and the throat types are necked shape, flaky shape, curved flaky shape and tube bundle shape. Using high-pressure mercury intrusion and constant-speed mercury intrusion to jointly characterize the pore structure, the study area reservoirs are divided into type Ⅰ and type Ⅱ based on the physical properties of the sample, mercury removal efficiency, drainage pressure and sorting coefficient. Based on pore classification standard of Hartmann et al, the pores are divided into macropores (>2.5 μm), mesopores (0.1￣2.5 μm), and micropores (<0.1 μm). According to the fractal theory, the average fractal dimension under different pore diameters in the study area is of 2.2￣2.8.The fractal dimension of macropores with small difference has obvious negative correlation with permeability contribution, while the correlation between mesopores and micropores is weak. The gas-water relative permeability experiment shows that the irreducible water saturation of samples in the study area is relatively large. The co-permeability zone of type Ⅰ is significantly larger than type Ⅱ. The gas-water displacement visualization experiment of real sandstone model has different displacement patterns according to the difference of the average fractal dimension of pore types and pore types under different pore sizes. Type Ⅰ is homogeneous displacement, and type Ⅱ is mesh fluid displacement and finger displacement. Therefore, type Ⅰ reservoirs with high macropore distribution frequency and low fractal dimension are the main targets for the exploration and development of tight gas reservoirs.

10.6056/dkyqt202302001