Research On Coupling Model Of Shale Gas Wellbore Flow And Horizontal Well Productivity

As a representative of emerging non-conventional energy sources,shale gas has the characteristics of large reserves,long production cycle and environmental protection,which is of great significance for safeguarding China's energy security.However,due to the complex geological characteristics of shale gas reservoirs,the economic development of shale gas reservoirs is difficult,horizontal well as one of the effective means of mining shale gas reservoirs have gradually became a hot topic.Based on the investigation of relevant literatures and the seepage mechanism of shale gas reservoirs,the horizontal well productivity of low-permeability gas reservoirs and shale gas reservoirs were studied.By coupling the wellbore pipe flow model with the horizontal well productivity model,a coupled model of shale gas wellbore flow-horizontal well productivity was established.Finally,the productivity model was verified and sensitivity analysis.This paper has achieved the following main research results:(1)Based on the principle of conformal transformation,combined with the seepage characteristics of low-permeability gas reservoirs,a single-phase and two-phase productivity model for horizontal wells in shale gas reservoirs were established.Through the sensitivity analysis of the productivity model,the results show:The productivity of single-phase horizontal wells in shale gas reservoir decreases with the increase of starting pressure gradient,stress sensitivity coefficient and reservoir anisotropy coefficient,and the impact of the three on gas well productivity is obvious.The production of two-phase horizontal wells decreases with the increase of water-gas volume ratio,and the water-gas volume ratio has a greater impact on gas well production.(2)According to the classical single-phase and two-phase flow model,the calculation of the pressure at the bottom of the actual shale gas reservoir and the pressure distribution in the horizontal wellbore was carried out.The results show that:The average coefficient method for calculating the bottom flow pressure of a single-phase flow gas well has higher accuracy.The influence of the relative density of natural gas on the bottom-hole flow pressure is greater than the influence of the borehole roughness on the bottom-hole flow pressure.When calculating the bottom-flow pressure of gas-water two-phase gas wells,the stability and accuracy of the M-B model is higher than that of the B-B model.The B-B model is susceptible to the daily water production of the gas wells and therefore the M-B model should be used when calculating the pressure distribution in the vertical section of the wellbore.(3)The pressure drop,along the process from the toe end to the heel end in the horizontal section of the gas well increases continuously.The change of the wall roughness has little influence on the pressure distribution in the wellbore.Appropriately,increasing the diameter of the well can effectively reduce the depth of the wellbore pressure loss,improve gas well production.When the horizontal section is gas-water two-phase flow,changing the volume ratio of water gas has a greater impact on the distribution of pressure in the wellbore.(4)Based on the principle of conformal transformation and the superposition principle of potential,according to the seepage characteristics of the horizontal wells in shale gas reservoirs and the fluid wellbore flow model,a coupled model of shale gas wellbore flow-horizontal well productivity was established.The example verification and sensitivity analysis of the productivity model show that:For the shale gas reservoir fracturing horizontal well single-phase productivity model,the error was 6.59%when calculated the gas well production.The length of the fractUre,the conductivity of the fracture,and the difference in the concentration of shale gas inside and outside the matrix increase the production of the single-phase fracturing horizontal well.For the shale gas reservoir fracturing horizontal well two-phase productivity model,the error was 5.28%when calculated the gas well production.The gas well productivity decreases with the increase of water vapor volume ratio and stress sensitivity coefficient,and increases with the number of fractures.The two-phase starting pressure gradient has little effect on the yield,and its influence on gas well production should be ignored.