多薄层致密砂岩储层大型水力压裂三维物理模拟实验

Three-dimensional physical simulation experiments on large-scale hydraulic fracturing in multi-thin interbedded tight sandstone reservoirs

房茂军 杜旭林 白玉湖 李昊 张浩 朱海燕

FANG Maojun DU Xulin BAI Yuhu LI Hao ZHANG Hao ZHU Haiyan

1. 中海油研究总院有限责任公司 非常规研究院, 北京 100028; 2. 中海石油(中国)有限公司 北京研究中心, 北京 100028; 3. 成都理工大学 “油气藏地质及开发工程”国家重点实验室, 成都 610059

1. Unconventional Research Department, CNOOC Research Institute Co., Ltd., Beijing 100028, China; 2. Beijing Research Center, CNOOC (China) Co., Ltd., Beijing 100028, China; 3. State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan 610059, China

鄂尔多斯盆地东北缘临兴气田以多薄互层型致密砂岩储层为主，储层岩性复杂、渗透率低，受多种因素影响且作用机理不明确，导致压裂施工难度大、效果差异大。为此，针对临兴气田致密砂岩储层不同岩石组分、黏土含量、粒径、沉积旋回、平面及纵向非均质性等特性，设计并开展了不同地质条件下的水力压裂室内大型三维物理模拟实验。根据相似准则，参照二叠系石盒子组三向地应力、岩石强度、井身结构参数、现场压裂施工参数，确定了实验基本参数。根据临兴气田典型井主力储层特征，制作了考虑不同岩石组分、黏土含量、粒径、沉积旋回组合、平面非均质性组合、纵向非均质性组合的15块立方体岩心，开展了15组压裂模拟实验，并从分析注入压力曲线和观察岩样破裂面两个方面总结了影响水力压裂缝扩展规律的储层主控因素。研究表明，岩石矿物和粒径、沉积旋回、平面及纵向非均质性对致密储层裂缝扩展形态有显著影响。砂岩粒度较大、胶结较弱、黏土含量较高、平面非均质性较强，使得裂缝面更易于屈曲，扩展压力增大，导致加砂困难；沉积旋回会使得水力压裂缝易于沿旋回层面扩展，从而形成水平缝，其中反旋回界面突破难度比正旋回大；由于砂—泥层间界面、砂—煤层间界面、天然砂岩弱面易被激活，从而产生“工”或“T”字形裂缝，对于砂泥多薄互层还会产生“工”+“T”+“十”字形的组合裂缝。实验研究揭示了不同地质条件下的水力压裂缝扩展形态，也为类似区块的研究提供了借鉴。

The Linxing gas field on the northeastern edge of Ordos Basin is mainly composed of multi-thin interbedded tight sandstone reservoirs. These reservoirs feature complex lithologies and low permeability, and are affected by multiple factors with unclear mechanisms, leading to difficulties in hydraulic fracturing operations and significant variability in operation outcomes. Therefore, this study designed and conducted a series of large-scale three-dimensional (3D) physical simulation experiments of hydraulic fracturing under different geological conditions, focusing on different rock components, clay contents, particle sizes, sedimentary cycles, and planar and longitudinal heterogeneities of the tight sandstone reservoirs in the Linxing gas field. According to the similarity criteria, the basic parameters of the experiments were determined by referencing the triaxial geostress, rock strength, wellbore structural parameters, and on-site fracturing operational parameters of the Permian Shihezi Formation. Based on the characteristics of the main reservoirs in typical wells of the Linxing gas field, 15 cubic rock cores were produced to account for different rock components, clay contents, particle sizes, sedimentary cycle combinations, and planar and longitudinal heterogeneity combinations. Fifteen sets of hydraulic fracturing simulation experiments were conducted, and the main controlling factors affecting the propagation of hydraulic fractures were summarized by analyzing the injection pressure curves and observing the fracture surfaces of rock samples. The results indicate that rock minerals, particle sizes, sedimentary cycles, and planar and longitudinal heterogeneities have a significant impact on fracture propagation patterns in tight reservoirs. The fracture surfaces are more prone to buckling with larger sandstone particle sizes, weaker cementation, higher clay content, and stronger planar heterogeneity, increasing the expansion pressure and difficulty in sand addition. Sedimentary cycles facilitate hydraulic fractures to propagate along the cycle planes, resulting in horizontal fractures. The difficulty of breaking through in retrograde cycle interfaces is greater than in prograde cycles. Interfaces between sand and mud layers, sand and coal layers, and natural weak sandstone surfaces are easily activated, leading to “工” or “T” shaped fractures. A combination of “工”, “T”, and “十” shaped fractures may occur in sand-mud multi-thin interlayers. This experimental study reveals the propagation patterns of hydraulic fractures under different geological conditions, providing insights for research in similar blocks.

中海油(有限)科技项目十四五重点攻关课题“多薄层致密气藏开发关键技术”(KJGG2022-1004)资助。

https://doi.org/10.11781/sysydz202404786