Research On The Depletion Pattern Of Shale Gas Based On Supercritical Adsorption

In shale gas reservoirs,where pore diameter can approach nano-scale,gas is in supercritical condition.At this scale,gas occurs in porous media in the form of conventional free gas state as well as adsorption state,i.e.supercritical adsorption.Furthermore,flow regime mechanism in shale gas reservoirs is different from that in conventional gas reservoir.Therefore,a new model is needed to describe supercritical adsorption and gas flow in this condition.The complex fracture network resulting from hydraulic fracturing in shale gas reservoirs makes it more difficult to characterize the depletion pattern of shale gas,which plays a vital role in the effective development of shale gas.This thesis will investigate the depletion pattern of shale gas based on supercritical adsorption.Based on supercritical adsorption,a simplified local density(SLD)model is built,which is solved by Peng Robinson state equation,and the distribution of shale gas along the pore is calculated.The results show that there is significant adsorption near pore wall and that the effect of pores and pressure on density distribution is significant,while the effect of temperature is minimal.Based on supercritical adsorption model,sing-tube apparent permeability mode is built with equation of motion and boundary conditions and then solved.The results show that apparent permeability increases with increment of pore diameter and decreases with increment of pressure.The pores are equivalent to resistances,for which a network model is built.Then the model is solved with four basic conversions and the rock permeability is acquired for a pore size distribution under reservoir conditions.The supercritical model is used to modify FMM and investigate the depletion pattern of shale gas reservoirs.The results show that supercritical model results in better depletion pattern compared with original model,that half length,number and conductivity of artificial fractures are dominant influence factors for depletion area and that half length,number and conductivity of artificial fractures are dominant influence factors for depletion degree,while length of natural fractures and natural fracture spacing are secondary influence factors.This thesis provides a basis for research on the supercritical adsorption in shale gas reservoirs,matrix apparent permeability and depletion pattern and provides a reference for parameter optimization of fractured horizontal wells in field shale gas production.