Numerical Simulation Of In-situ Pyrolysis Of Oil Shale

In-situ pyrolysis is an important method for deep oil shale mining.Due to the limitation of heating range,large-scale mining cannot be realized.At present,experimental research is the main method.In order to reveal the synergetic relationship between pyrolysis,flow,rock deformation and other multiple actions in the process of in-situ pyrolysis,enhance the ground controllability,and promote the large-scale development test of mineral resources,it is of great significance to carry out numerical simulation research on in-situ pyrolysis of oil shale.The paper first analyzes the multiple physical and chemical fields involved in the pyrolysis process of oil shale,and selects appropriate mathematical models and parameters for numerical simulation.The pyrolysis process of oil shale is divided and the pyrolysis mechanism of oil shale is explored by establishing a two-dimensional THC three field coupling model.Analyzed the effects of different heating temperatures on oil and gas phase production and product rate.The solid mechanics field is added to create a THMC four field coupling model that takes into account changes in porosity and permeability during pyrolysis,focusing on the change laws of the temperature,pressur,porosity,permeability,and stress-strain field during pyrolysis,as well as the effect of formation depth on oil shale pyrolysis production,forming the theoretical basis of multi field coupling.The research results indicate that: The main reaction is not always constant in the process of oil shale pyrolysis,and gradually transforms from kerogen pyrolysis to oil phase pyrolysis.According to the main pyrolysis reaction and the average concentration of products,the pyrolysis process of oil shale can be divided into four stages: kerogen pyrolysis,kerogen and oil phase pyrolysis,oil phase pyrolysis,and light oil pyrolysis.The highest oil production occurs during the pyrolysis stage of kerogen.During the pyrolysis of oil shale,the migration of all pyrolysis products is dominated by diffusion at first,and then gradually changes to convection.At the same heating temperature,the higher the initial temperature and pressure,the greater the production of oil phase and hydrocarbon gas.The gas production rate during pyrolysis is much higher than the oil production rate,with a difference of about three times between the two.The structural change of oil shale reservoir is mainly affected by chemical reaction,fluid seepage and heat transfer.The total strain of rocks during pyrolysis is mainly thermal strain.The research results further improve the theory of in-situ pyrolysis of oil shale and provide a basis for field engineering practice.