Brittleness Evaluation Method of Shale Gas Reservoir Based on Acoustic P-wave and S-wave Testing of Rock Samples and Its Logging Application

As a clean energy, the development technology of shale gas is relatively mature worldwide, and the research methods are also remarkably extensive. Research on rock physical properties of shale gas reservoirs is one of the key technologies. Considering Chinese shale gas exploration blocks, Sinopec focal dam and Gaoyou sag block are markedly successful. This paper comprehensively analyzes the compressibility of this block based on P-wave and S-wave tests of rocks and the logging data to guide the fracturing design of this block scientifi cally. First, five samples (2.5 cm in diameter, length of 4-6 cm) are drilled from the cores in the laboratory (drilling is conducted in the shale gas layer). Second, the saturated water sample is placed into an HR2500-2 high-speed refrigerated centrifuge, and eight speeds are used to dehydrate simulation samples in diff erent water saturations. Third, the samples are then placed under simulated conditions of formation to determine their P-wave and S-wave velocities by using the CTS-45 nonmetal ultrasonic testing analyzer. Finally, combining experimental data with the calculation method of rock mechanics parameters, a series of parameters, such as Poisson's ratio, Young's modulus, and brittleness index, can be obtained. Results obtained from the aforementioned methods for five wells of Gaoyou sag block show that a high Young's modulus and a low Poisson's ratio increase brittleness and strengthen fracturing performance. Overall, the ElF4 interval of each small layer fracturing level provides scientifi c guidance to the fracturing design.