Study On The Mechanism Of Removing Water Lock By Injecting Hot Gas For T12 Tight Gas Reservoir

Among the total proven natural gas reserves in China,Tight gas accounts for about 40% of the total.Tight gas has rich reserves and resource potential,which has become an important field of natural gas exploration and development.Efficient utilization of tight gas reservoirs can effectively improve China’s natural gas energy reserves,which is of great significance to national dependence on natural gas imports and alleviate the contradiction between supply and demand of natural gas.Tight gas reservoirs are characterized by ultra-low porosity,ultra-low permeability,micro-fractures,capillary tubes,rich clay minerals,etc.The water lock damage probability of reservoirs is high and the damage degree is high.A large number of experimental results show that the water lock damage of tight gas reservoir can reach more than 70%,and the partial damage rate is as high as 90%,which seriously affects the effect of tight gas reservoir.In this paper,the change and distribution of irreducible water in different stages are determined by combining hot gas injection test with nuclear magnetic resonance test.The mechanism of drying tight core by hot gas injection is studied from core scale and pore scale.Based on the digital core,the pore flow and "drying" of heat injection gas in tight gas reservoir are simulated by means of numerical simulation considering external conditions such as pressure and temperature,and the Mixture multiphase flow model is used to study the driving and influencing factors of gas/liquid phase state in core displacement,and the ability of releasing water lock of gas reservoir core water saturation is characterized.On the basis of the geological model,numerical simulation is carried out to study the drying effect of heat injection gas on reservoir and its influence on gas well productivity.Corresponding to the previous work,the technical limit of heat injection gas drying is further formed,and the understanding and understanding of the "drying" mechanism of heat injection gas are strengthened to complete the research on releasing water lock by heat injection gas.The results show that the order of influence of various factors on permeability recovery and water saturation is as follows: gas injection temperature,gas injection rate,permeability type,gas type,the higher the gas injection temperature,the greater the injection rate,the better the core drying effect.Nuclear magnetic resonance experiments show that the water in the larger pore size is preferentially displaced after gas injection,and the smaller the pore,the more difficult it is for the water phase in the pore to be swept by the gas phase;The movable water in the core mainly exists in the middle pores,but with the increase of porosity and permeability,the movable water in the large pores gradually increases,and the irreducible water in the small pores accounts for a large proportion.The change of core water saturation shows a trend of "first rapid and then slow".When the gas injection rate is 300～450PV,the permeability recovery rate reaches the fastest,and gradually tends to be stable when the gas injection rate is greater than 600PV;The change of core water saturation shows a trend of "first rapid and then slow".When the gas injection rate is 150～300PV,the change of core water saturation tends to be stable gradually after the gas injection rate is more than 450 PV.The numerical simulation results show that the residual water phase in the pore mainly exists in the corner blind end pore and throat with the pore channel;Factors such as structural temperature and pressure will affect the drying effect,the simpler the pore structure,the higher the injection temperature,the larger the displacement pressure difference and the smaller the wetting angle,the better the core drying effect;Reservoir numerical simulation shows that the higher the temperature,the faster the speed,the more the water saturation of the reservoir,the greater the recovery of gas production productivity,and the better the drying effect.At the same time,it is considered that injecting high temperature gas can effectively relieve the damage of water lock permeability in gas wells and improve the production of gas reservoirs,which has guiding significance and application value in actual production.The conclusion of this study can provide theoretical basis and practical guidance for enhanced oil recovery in tight gas reservoirs,and has important theoretical significance and practical application value for unlocking water lock damage and improving gas seepage ability in tight gas reservoirs.