Feasibility Studies Of Cyclic Liquid Injection For Tight-Low Permeability Reservoirs

In tight-low permeability reservoirs,the oil in matrix is difficult to drive,fractures lead to serious water/gas channeling,and the effectiveness of conventional production methods is poor,a study on the adaptability of cyclic liquid injection was carried out..Artificial tight-low permeability homogeneous and heterogeneous cores were used for water flooding experiments.Based on the comprehensive analysis of the experimental results,a basic understanding of the water flooding characteristics of tight-low permeability reservoirs is obtained—with the decrease of the matrix permeability,the water flooding efficiency is greatly reduced,and the water flooding pressure difference increases sharply.The lower the permeability,the more serious the water channeling in the heterogeneous(fractured)reservoirs,and the lower the recovery.The contradiction between the difficulty of driving oil in tight matrix and strong water channeling is the main reason to restrict the adaptability of conventional water flooding in tight-low permeability reservoirs.Aiming at the main contradiction faced in the production of tight-low permeability reservoirs,the research on the adaptability of cyclic liquid injection was carried out starting from the mechanism.A new experiment that can simulate the energy storage scale and release rate of the actual reservoirs is used to carry out the cyclic liquid injection experiment.It is found that with the increase of the hydrophilicity,the effect of cyclic liquid injection is significantly improved,which shows that imbibition is one of the main mechanisms.The results of local pressure difference during the cyclic liquid injection experiment show that it can effectively drive the oil in the matrix.The synergistic effect of imbibition and local pressure difference in cyclic liquid injection to improve the oil recovery in matrix is a potential method of production in tight-low permeability reservoirs.The experiment method was used to study the factors and related laws of cyclic liquid injection in tight-low permeability reservoirs.The matrix recovery decreases monotonically with the pressure release rate.When the pressure release rate increases from 4673 k Pa/PV to 10213 k Pa/PV,the matrix recovery decreases from 29.01% to12.5%.The pressure release rate is a sensitive factor that affects the effectiveness of production.The matrix recovery in unsteady experiment is 5.66% higher than the conventional experiment,and more oil is produced in the second and third round.Moderately increasing the viscosity of the injection fluid can significantly improve the effect.According to the experimental results,an unsteady production method for tight-low permeability reservoirs with reasonable pressure release rate is proposed.