Physical Simulation And Application Of Seepage Mechanism In Late Development Stage Of SXM Tight Gas Reservoir

SXM gas reservoir is a typical tight sandstone gas reservoir.With characteristics of tight reservoir,strong heterogeneous,high water saturation and complex gas-water seepage relationship,the current recovery rate is only 28%.The remaining recoverable reserves to be developed are still quite large and have the potential for further development.Which requires a full understanding of the pore-permeability characteristics and gas-water seepage characteristics of the gas reservoir at the later stage of development.So as to better provide theoretical support for gas reservoir recovery.With a full understanding of the present situation of SXM tight gas reservoir development,based on reservoir core model,this paper comprehensively applies NMR,stress sensitivity,start-up pressure gradient and multi-layer production of parallel long cores,and combines gas-water two-phase percolation theory to develop reservoir pore structure,core fluid distribution,gas-water two-phase percolation characteristics and many others for SXM tight gas reservoir.Finally,combining with the productivity formula of gas wells,the practical application analysis of productivity change is further carried out,and the following understandings are obtained as follows:(1)The whole belongs to medium pore and ultra-low permeability type with strong reservoir heterogeneity and poor pore throat connectivity.Gas-water seepage channel is mostly larger pore with pore diameter greater than 0.2 micron,and core stress sensitivity is strong.(2)Start-up pressure exists in gas-water two-phase seepage of reservoir,and the increase of water saturation or the decrease of pressure will greatly increase the start-up pressure gradient;Besides,the core is strong hydrophilic,and the co-seepage area of gas-water two-phase seepage is small.It also has a large seepage resistance,the change of pressure mainly affects the two-phase seepage ability of gas-water drive,.What's more,the effect of relieving water lock is poor.(3)To some extent,the development mode of combination of depletion and water flooding in fractured reservoirs increases the recovery degree of fractured reservoirs.Increasing water saturation will reduce the gas productivity of different reservoirs and gradually inhibit the production of low permeability reservoirs.Reservoir productivity get higher when formation pressure is higher.Appropriate increase of production pressure difference is beneficial for reservoirs to better exert their percolation advantages.Generally speaking,in different periods of gas well production,the contribution of high permeability reservoirs to production is relatively more.(4)Combining the experimental results with the actual situation of gas wells in gas reservoirs,a vertical fracture productivity model considering start-up pressure,stress sensitivity,water-gas ratio and half-length of fractures is established.The analysis shows that stress sensitivity and water production of gas wells have the greatest impact on productivity.Therefore,in actual production of gas reservoirs,production pressure differential should be reasonably set up to reduce the hazards caused by stress sensitivity,slow down water invasion,and control the fracture half-length within the optimal fracture half-length of 50?60m.