Research On Flow Simulation Of Tight Gas Reservoirs Considering Reservoir Drying Effect

China is rich in tight gas resources,with recoverable resources exceeding 10 trillion cubic meters,accounting for more than 40%of the proven natural gas reserves,with huge potential.The efficient development and utilization of tight gas resources are of great strategic significance for alleviating the contradiction between natural gas supply and demand in China,reducing the external dependence of energy and ensuring national energy security.Tight gas reservoirs are generally characterized by low porosity,low permeability,fracture development,prominent capillarity and high original irreducible water saturation,which leads to widespread "water lock" phenomenon in gas reservoirs,serious obstruction of gas percolation,and many difficulties in efficient development of gas reservoirs.The "drying" of the reservoir can evaporate the formation water in the wellbore and its vicinity,reduce the drag of the matrix near the fracture surface and the micro-fracture channel,improve the reserves production rate and recovery rate,and effectively solve the problem of "water lock".At home and abroad on the mechanism of reservoir "dry" little research,numerical simulation research,characterization of the dense gas reservoir in conventional numerical simulation method can not micro flow characteristics of microscale effect,and indoor experiment of core flow time-consuming,and not under the geological conditions of actual simulation flow,at this point,the mesoscopic lattice Boltzmann method(LBM)has become a very good choice.Therefore,based on lattice Boltzmann method,this paper studies the flow law of single-phase gas and gas-water two-phase in tight reservoir and the influence of"drying" effect on the flow capacity of tight gas.The main work of this paper is as follows:(1)Considering the real reservoir temperature,pressure and pore throat diameter of tight gas reservoir,the dense gas flow pattern was drawn,and the results showed that the flow of tight gas was a slip flow and a weak continuous flow.Considering the micro-scale effect,boundary slip correction and gas denseness,the flow of tight gas in flat pores was studied.The results showed that the micro-scale effect had a promoting effect on the flow capacity of tight gas,and the higher the pressure was,the weaker the promoting effect was,the higher the temperature was,the stronger the promoting effect was,and the smaller the pore diameter was,the stronger the promoting effect was.In the weak continuous flow region,the Knudsen number has no effect on the flow and conforms to the non-slip flow characteristics.In the slip flow area,the effect of micro-scale effect on the improvement of tight gas flow capacity has a good linear relationship with Knudsen number,and the ratio of apparent permeability to natural permeability in the slip flow area is predicted to be 2.27 at most.(2)Considering different pore throat structure and Knudsen number distribution,the influence of pore throat structure on tight gas flow was studied,and the results showed that the presence of throat made the non-linear distribution characteristics of pressure significant.With the increase of pore throat ratio,the gas pressure on both sides of throat tended to be consistent,and the gas pressure drop was mainly concentrated in the throat position.The non-linear distribution of pressure significantly reduces the gas flow velocity,which leads to the rapid decrease of tight gas permeability.(3)The multi-component multiphase flow LB model was used to simulate the gas-water two-phase flow at the pore scale under the formation conditions.The existence of bound water can be divided into four types:blind end pore water,dead pore water,connected channel wall adsorbed water film and blocked water.The presence of high velocity flow in the narrow throat of a large passage has important effects on the flow capacity of tight gas.(4)Equivalent treatment of "drying" effect was conducted to study the influence of different "drying" intensity on tight gas seepage capacity.The results showed that the ratio of tight gas permeability before and after "drying" was positively correlated with the rate of bound water consumption of "drying" effect,and the "drying" effect could effectively improve the seepage capacity of tight gas.The research results in this paper have laid a theoretical foundation for the simulation of micro-flow in tight gas reservoirs and provided a new research idea for the simulation of"drying" flow in tight reservoirs.