Research On The Characteristics Of Water Invasion Mechanism Of Gas Reservoirs In Kela 2 Low Permeability Area

The Kela-2 gas reservoir is located in the eastern section of the Kelasu tectonic belt in the Kuqa Depression of the Tarim Basin.It is currently the largest known continental gas field in China.It belongs to the abnormal high-pressure edge-bottom water gas reservoir and has under-compacting characteristics.In the process of exhaustive development,the formation pressure gradually decreases,but the overburden pressure does not change,and the effective stress acting on the rock particles increases.This effect may cause rock deformation,and the physical parameters of the rock change,so that the stress sensitivity affects the water intrusion of the bottom and the development of the gas reservoir.In the physical simulation experiment of conventional depletion,the influence of stress sensitivity on gas reservoir invasion and gas reservoir development is not considered,and the understanding of water invasion is not accurate.Therefore,the study on the effect of water intrusion on gas recovery in the low-permeability gas reservoir of Kela-2 can more accurately understand the water intrusion mechanism under stress-sensitive conditions and the factors affecting gas recovery.It has an important guiding role in the development of gas reservoir follow-up programs.Based on the actual production situation,this paper compares the conventional full-diameter depleted water intrusion experiment with the simulated overburden pressure full-diameter depleted water intrusion experiment,and combines the stress sensitivity experiment,the stress-sensitive mathematical model and the depleted numerical simulation to systematically study the Kela-2 gas reservoir that the effect of different speeds and different rock structures on gas recovery when considering stress-sensitive conditions.This article mainly achieves the following understanding:(1)The velocity sensitivity of the Kela-2 core increases first and then decreases with the increase of the speed of depletion.Under the same kind of core,the faster the depletion speed,the earlier the water breakthrough time,the lower the cumulative recovery rate,and the cumulative recovery rate increases first and then decreases.(2)Because of the existence of fracture high-permeability zone in the fracture core,the flow velocity of the water is much faster than that in the pore core,and the recovery rate of the fracture core is lower at the same rate of depletion,and the water breakthrough time is earlier;(3)As the effective stress increases,the rock skeleton deforms,and the porosity and permeability of the core change,slowing the flow velocity of gas and water,delaying the water breakthrough time and increasing the gas recovery.The stress sensitivity of the Kela-2 gas reservoir is weak.And the loss of permeability is less than 30%,which has little effect on gas reservoir development.(4)Deriving the water time formula of fracture gas reservoirs with stress sensitivity,gas non-Darcy and other factors.Gas non-Darcy effect and fracture development will increase the gas flow rate and increase the water breakthrough time.Stress-sensitive effects slow the flow rate of the water and prolong the breakthrough time of the water.