Numerical simulation and field test of grouting in Nong'an pilot project of in-situ conversion of oil shale

In-situ recovery of oil from oil shale using the convection heating method requires a hydraulic fracturing process to provide transportable channels for thermal carriers and shale oil and gas released by oil-shale pyrolysis. However, flowing groundwater could enter the reaction zone through fissures generated by hydraulic fracturing, causing significant heat loss and blocking the generation and outflow of oil and gas during the heating process of the in-situ conversion of oil shale. Therefore, a continuous water-stop is indispensable. This study optimized the layout of grouting wells in a hexagonal pattern and carried out a series of grouting diffusion simulations according to the hydrogeological data of the Nong'an oil shale stratum. Moreover, a field test was conducted at the site of the Nong'an pilot project of oil shale in-situ processing. The simulation result indicates that the production wells should be kept open during the grouting process, as numerous local high-velocity zones of groundwater between the grouting wells could restrict the expansion and intersection of grouting. An optimized open pattern grouting method for the Nong'an pilot project was proposed, and a well-spacing of 3 m was determined to be appropriate. Finally, in the field grouting test, the fine grout intersection without local high-velocity zones was verified through water pressure tests and according to the initial and ultimate outflow of groundwater in the production well of the field test, which corresponded to the simulation result. Hence, the authenticity of the grouting method determined by numerical simulation has been verified.