A Method for Determining the Contribution of Adsorption Gas to the Production of Shale Gas Wells

A better method for determining the contribution rate of adsorption gas during the shale gas production after multi-stage fracturing,was developed that takes into consideration stress sensitivity,diffusion and adsorption according to three models,(i.e.formation pressure distribution computation model,adsorption gas production computation model and free gas production model).The goal was to develop a procedure for practical application in domestic shale gas wells.The results showed that the method could be used to calculate the formation pressure distribution,the change of dynamic reserves,output of adsorption gas and free gas.The results were also successful in that they show that although original reserve of adsorption gas accounts for about 30% of that of free gas,the desorption is not obvious due to the Langmuir adsorption pressure(6 MPa)is lower than the current bottom-hole pressure(12 MPa).Although this well has been put into production for 25 000 h,the adsorption gas production is only increased from initial 9.0% to 10.5% now.Somewhat surprisingly,research results indicated that the contribution of adsorption gas was limited in spite of its considerable reserves in some Chinese shale gas reservoirs,and ultimate recoverable reserves were very low.This method can provide some theoretical references for future improvements of the fracturing performance,and for better modeling of the production and dynamic reserves in a shale gas well.