柴达木盆地东坪基岩气藏裂缝发育规律研究

Patterns and Comprehensive Predictions of Fracture Development in Bedrock Gas Reservoirs in Dongping, Qaidam Basin

李翔 刘应如 柴小颖 龙伟 白亚东

LIXiang LIUYingru CHAIXiaoying LONGWei BAIYadong

中国石油勘探开发研究院西北分院, 甘肃 兰州 730020 中国石油青海油田勘探开发研究院, 甘肃 敦煌 736202

Northwest Branch of PetroChina Research Institute of Petroleum Exploration and Development, Lanzhou, Gansu 730020, China Research Institute of Exploration and Development, Qinghai Oilfield Ccompany, Petrochina, Dunhuang, Gansu 736202, China

东坪基岩气藏位于柴达木盆地西北部阿尔金山前东段，是新近发现的中国内陆盆地最大规模基岩古潜山整装气藏。但由于该区基底片麻岩、花岗岩天然裂缝及溶蚀孔洞发育，且成因复杂，非均质性强，单井产量差异大，该气藏的规模上产开发存在较大难度。裂缝是影响基岩储层高产稳产的关键因素，因此，开展该气藏的裂缝发育规律及综合预测研究显得格外重要。为此，在认识其岩性、物性和气藏类型基础上，基于岩芯、薄片以及成像测井等进行了分析统计，明确了东坪基岩以构造缝为主，两类溶蚀裂缝为辅的裂缝系统。通过单井统计结果标定，实现研究区岩性分带，基于叠后振幅方位分解技术实现研究区裂缝平面展布预测。最终结合产能统计分析，通过不同岩性带、不同裂缝类型与产能及改造效果的相对关系，将研究区划分为3个有效裂缝发育区，其中，一个自然产能高效区，两个措施改造潜力区，实现了对研究区储层的综合预测，预测结果与实际产能吻合率均达70%以上，为后续开发调整提供支撑。

Located in the front eastern section of the Altyn-Tagh in the northwestern Qaidam Basin, the Dongping bedrock reservoir is the largest complete bedrock buried hill gas reservoir recently discovered in the terrestrial basins of China. Nevertheless, due to natural fractures in gneiss and granite bedrocks and karst caves in the region and their complex formations, the area is highly heterogeneous with significant yield differences between wells. In addition, mass exploitation of a large-scale gas reservoir is relatively difficult. Because fractures are the key factor in allowing high and stable yields of bedrock reservoirs, it is especially important to conduct research on patterns and comprehensive predictions of fracture development in the reservoir of interest. Hence, lithological and physical properties and reserve types of the reservoir were examined, followed by statistical analyses based on core samples, thin sections, and well imaging. We found that the fracture system of the Dongping bedrock reservoir is dominated by tectonic fractures, accompanied by two types of dissolution fractures. The statistics of individual wells were used as standards to divide the study area according to its lithology. The Post-Stack Amplitude Direction Decomposition (PADD) technique was employed to predict the horizontal distribution of fractures in the study area. Finally, the results were integrated and analyzed with yield data. According to the relative relationships between different lithological zones, different fracture types, yields, and transformation effects, the study area was divided into three effective fracture development zones. One is a natural high-yield zone, while the other two are potential areas requiring appropriate transformation measures. Comprehensive predictions of reservoir potential in the study area were performed, and the predicted results matched actual yields at a rate higher than 70%.

10.11885/j.issn.1674-5086.2017.11.15.01