| Natural gas reservoirs are widely distributed in China.According to incomplete statistics,the resources of low-permeability gas are abundant with more than 10 trillion square meters,accounting for about 20%.In the 21st century,the exploration and exploitation of natural gas in China is booming.Compared with traditional gas reservoirs,the low-permeability gas reservoirs are characterized by lower permeability,smaller porosity and poorer connectivity,which objectively increases the difficulty of exploitation.How to develop low permeability gas reservoirs economically has become the focus of current research.Dynamic simulation of gas wells in low permeability gas reservoirs is the foundation of gas well productivity prediction,gas reservoir development index prediction,and gas reservoir development plan for low permeability gas reservoirs.However,the dynamic simulation of low permeability gas reservoirs is more complicated than that of conventional gas reservoirs due to some special effects,such as stress sensitivity,non-Darcy flow,etc.In addition,in order to achieve effective development of gas reservoirs,dynamic monitoring of gas reservoirs is generally required.In addition to production and temperature,the most basic is to monitor the wellbore pressure of the gas wells.If a downhole pressure gauge is placed,the downhole pressure condition can be directly monitored,and the pressure data obtained is consistent with the conditions of the gas well pressure in the seepage model,both of which are bottom hole pressures.However,due to some reasons,the bottom hole data obtained by monitoring are often less,while the wellhead pressure and production data are more,so it is necessary to simulate the situation in the wellbore,and combine the gas reservoir seepage model with the wellbore pipe flow model to predict the performance of gas wells in low permeability gas reservoirs.In view of these problems,a wide range of investigations have been carried out in this paper.On the basis of considering the influence of stress sensitivity and non-Darcy flow on the seepage of low-permeability gas reservoirs and the influence of gas-water two-phase flow on the wellbore tube flow,the seepage and gas water in the formation are analyzed.The tube flow in the wellbore is coupled to realize the dynamic simulation of the low permeability gas reservoir under the coupling of the wellbore and the formation.The main achievements of this paper are as follows:(1)The percolation mechanism of low permeability gas reservoir is clarified,the two-dimensional gas-water two-phase flow model of fractured low permeability gas reservoir is established,and the numerical solution of the model is carried out.(2)The effects of stress sensitivity and non-Darcy flow on gas-water two-phase seepage in low permeability gas reservoirs are clarified,and the effects are analyzed.(3)The flow process of natural gas in gas wellbore is defined.And based on the gas-water two-phase pipe flow wellbore pressure calculation model under the influence of geothermal gradient,the gas-water two-phase pipe flow calculation program is compiled(4)Coupling wellbore model with formation model,and based on Visual Basic language,a two-dimensional two-phase flow simulation software for abnormally high pressure fractured low permeability gas reservoir with two holes and two permeability is developed.The simulation results are compared with those of existing commercial software,which verifies the correctness of the model and the self-compiled software.(5)Using self-programming dynamic simulation software,the prediction of production,pressure,and saturation distribution is realized... |
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