Simulation experiment of reasonable production pressure difference in Jurassic tight reservoirs,central Sichuan Basin
The Jurassic tight reservoirs in central Sichuan Basin are featured by ultra-low porosity and permeability.During the pro-duction process,the reservoirs show the seepage characteristics of high start-up pressure gradient,strong stress sensitivity,and ma-trix-fracture dual-medium flow.The fracture system and the elastic energy of crude oil are the main drive in the initial stage of gas well production.Reasonably controlling the production pressure difference,reducing the stress sensitivity damage,and maximizing the utilization of comprehensive formation energy are crucial to the development of such reservoirs.By means of laboratory experiment with tight cores and gas-bearing crude oil samples,fractured core and matrix core were connected in series to simulate the reservoir environment near and far away from wellbore area after fracturing,so as to determine the reasonable production pressure difference in tight reservoirs.The following results are obtained.(i)The simulation test is divided into two stages:unsteady flow test and steady flow test.The former is characterized by fracture-rock flow,low displacement pressure,delay of matrix-rock supply,and rapid decline of oil and gas production.In the latter stage,with the increasing difference of experimental displacement pressure,the fluids in ma-trix core begin to flow to fractured core,the flow rate exhibits an obvious inflection point with the increase of displacement pressure difference,i.e.,the maximum production.(ii)When the outlet pressure is lower than the bubble point pressure,the in-place oil is de-gassed in the core.The greater the permeability of the fractured core,the stronger the seepage capacity,and the stronger the ability to overcome the two-phase flow resistance.The decline in the oil-phase relative permeability and the rise in the gas-oil ratio of produced fluids slow down.The oil production shows a trend of first rising then falling.(iii)With the increase of experimental displacement pressure difference,the oil-phase flow velocity per unit area begins to decrease,the production pressure difference corresponding to the yield is the maximum reasonable production pressure difference.The laboratory experiment fully considers the mixed wetting and nonlinear seepage effects of tight reservoirs,and the test results are more in line with the field data.It can effectively improve the cer-tainty of reasonable production pressure difference in depletion exploitation of tight reservoirs,and also provide basic parameters and theoretical basis for early-stage reasonable production allocation of single well.
Central Sichuan BasinJurassicTight reservoirFractured coreEarly stage of depletion exploitationReasonable pro-duction pressure difference
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维普
