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.