Experimental Study On Heterogeneous Gas Supply Mechanism Of Low Permeability Gas Reservoirs

China's low permeability reservoirs have abundant resources,large proven reserves and strong development potential.In the proven reserves,the low permeability gas reserves account for about 40%.In large and medium-sized gas fields,low permeability gas reservoirs account for about 60%of the gas reserves.Over the past 15 years,the exploration and development of low permeability gas reservoir is more and more attention in our country,several large low permeability gas field was discovered and put into production in succession,occupies an important position in the domestic natural gas industry.Most of the low permeability reservoirs in China have low porosity,low permeability,high water saturation and strong heterogeneity.The characteristics of low permeability gas reservoir is strong heterogeneity can affect production and development of low permeability gas reservoir,as a result,our predecessors on low permeability heterogeneous gas reservoir in a lot of theoretical research and experimental research,and achieved some results.But most of the experimental study is carried out under low pressure,with the actual conditions of formation pressure difference is big,to know the true formation pressure gas reservoir pressure and production characteristics under the condition of existence insufficiency,so it is necessary under the condition of real formation pressure for heterogeneous experimental study on the mechanism of low permeability gas reservoir gas supply.The offshore A gas field is a large-scale low-permeability gas field discovered in China.It uses the offshore A gas field as the research object,improves the existing test methods,and establishes a parallel/serial physical simulation device for high-pressure constant-flow failure,systematically studying the permeability differential,formation pressure and mining.The influence of gas velocity on the dynamic characteristics of gas reservoir exploitation has been carried out.There are 12 experimental groups for the mechanism of heterogeneous gas supply between the layers,and 15 experimental groups for the plane gas supply mechanism.The main conclusions are as follows:(1)The gas supply characteristics of interlayer heterogeneity low permeability gas reservoir.1)In the stable period,the instantaneous gas production velocity of the high permeability region is greater than that of the low permeability region.At the end of the stable production period,the instantaneous gas production volume and the instantaneous gas production in the high-permeability region decreased rapidly.In the descending process,the instantaneous gas production volume of the low permeability region is greater than that of the instantaneous gas production.With the increase of gas recovery,the stable production time of gas reservoir gradually decreases.2)With the increase of distribution,the total recovery rate of the gas reservoir gradually decreased,but the overall difference was not large,which was about 80%.The ultimate recovery rate of high permeability area is greater than that of low permeability region.3)When the initial pressure of high permeability zone and low permeability area is inconsistent,the pressure reverse irrigation phenomenon will occur at the beginning of the experiment.And with the decrease of the distribution,the increase of gas channeling,the more serious the interlayer interference phenomenon.Therefore,in order to reduce the influence of interlayer interference,the production should be increased appropriately in actual production.(2)Gas supply characteristics of plane heterogeneous low permeability gas reservoirs.1)In the stable period,the instantaneous gas production velocity of the high permeability region is greater than that of the low permeability region.At the end of the stable production period,the instantaneous gas production volume and the instantaneous gas production in the high-permeability region decreased rapidly.With the increase of distribution,the stable production time of gas reservoir gradually decreased.2)The faster the gas recovery,the faster the gas reservoir will be abandoned.Moreover,the single-layer pressure difference of low permeability zone is increasing with the single layer pressure difference in the high-permeability zone.During the whole experiment,the single-layer pressure difference in the high-permeability zone(maximum 2MPa)is greater than that in the low-permeability region,and the trend of the first increase and then decrease is presented.3)The higher the gas recovery rate,the total recovery rate of the gas reservoir gradually decreased,but the overall difference was not large,which was about 80%.,and the final recovery rate of the high-permeability region is greater than that of the low permeability region.