Research and Application of Technology to Improve the Permeability of Maoming Oil Shale in China

摘要

Oil shale, one of the world's richest energy resources, is considered a very important alternative energy in the 21st century. In recent years, oil shale in-situ exploitation technology has advanced significantly, such as In-situ Conversion Process of Shell and in-situ heating with fluid. The property of low porosity and low permeability makes it hard to inject thermal fluid into oil shale formations. For in-situ heating with fluid, some stimulation of the oil shale formation is needed so that it can have sufficient permeability. For Maoming oil shale in China, clay minerals are the main constituent. The total content of kaolinite, hydromica and montmorillonite ranges from 50% to 70%, whereas the total content of brittle minerals ranges from 30% to 40%. This feature of mineral composition results in difficulty of getting a network of fractures using hydraulic fracturing. In this study, the Pulse Power Fracturing Technology (PPFT) and Treatment Agent Post-processing Technology (TAPT) were designed for the stimulation of oil shale formation. The energy used in PPFT was optimized in combination with characteristics of Maoming oil shale. Treatment agents were developed and their performances were investigated. Experimental results showed that the porosity, pyrolysis rate, and oil yield rate of oil shale samples from Maoming increased by more than 25% after it reacted with the treating agent. During stimulation, PPFT broke the oil shale formation at first, and then TAPT further improved its permeability. After this process, the morphology of fracturing could meet the requirement for the injection of thermal fluid. PPFT was applied in the Maoming block, and it broke the oil shale formation with designed energy scale which was optimized by laboratory experiments. During the process of operation, both ultrasonic testing technique and hydraulic pressure drop testing technology were used to detect and analyze the results of this treatment. Practice has proven that PPFT could break oil shale formation effectively and the retrofit distance could surpass 15 meters. This study describes effective means for increasing the permeability of oil shale, providing an important and useful support for the technical development and application of oil shale in-situ heating with thermal fluid.