干热岩热储体积改造技术研究与试验

干热岩的岩性、力学特性和开发利用方式与常规油气资源相比差异较大，其储层改造不能直接采用页岩油气与致密砂岩油气压裂技术，需要研究适用于干热岩的改造技术。为此，利用井下花岗岩岩心和大尺寸露头岩样，采用高温测试和真三轴物理模拟系统，测试分析了高温岩石力学特性，模拟研究了裂缝起裂与扩展形态特征，分析了高温下花岗岩的脆塑性、岩石破坏特性以及天然裂缝对裂缝破裂压力、扩展路径和形态的影响特征，提出了“低排量热破裂+胶液扩缝+变排量循环注入”体积改造技术，并进行了现场试验，验证了室内研究结果。研究表明，花岗岩在高温下塑性强、脆性差、水平应力差大，岩石以张性和剪切混合破坏为主，天然裂缝和温差效应可显著降低破裂压力、提高裂缝复杂性与改造体积。研究结果对于干热岩热储高效开发具有较好的指导作用。 

Research and Test on the Stimulated Reservoir Volume Technology of Hot Dry Rock

Compared with conventional oil and gas resources, the lithology, mechanical properties, development and utilization methods for simulating reservoir volume in hot dry rock are quite different. The fracturing technologies for shale and tight sandstone cannot be directly used in hot dry rocks, and it is necessary to study a fracturing technology that is suitable for the stimulation of hot dry rock. To this end, the mechanical properties of rocks under high-temperature conditions were tested and analyzed by using downhole granite cores and large-size outcrop samples. By adopting high-temperature testing and true tri-axial physical simulation systems, it was possible to simulate and study the morphological characteristics of crack initiation and propagation. The characteristics of brittle-plastic granite at high temperature, rock failure features and the effect of natural fractures on the fracture pressure, propagation path and morphology were analyzed. On this basis, a stimulated reservoir volume technology of low flowrate thermal fracture + gel expanding of cracks + variable flowrate cyclic injection was proposed. A pilot fracturing program at well site was conducted to verify the results of indoor research. Studies suggested that granite had a strong plasticity, poor brittleness, and a large horizontal stress difference at high temperatures. The rock is mainly damaged by tension-shear failure, and natural fractures and temperature difference effect can significantly reduce the fracture pressure, increase the complexity of fractures and achieve a stimulated reservoir volume. The research results can provide a good guidance and best practices for the efficient development of hot dry rock reservoirs.