Prediction of Dynamic Reserves of Shale Gas with Modified Flow Rate Transient Approach

Shale gas is an unconventional reservoir,which is widely distributed all over the world;it has an increasing proportion in natural gas production in recent years.Shale gas reservoirs have very low porosity and permeability,and main features of the well test are low or no productivity as well as slow pressure buildup.In addition,the presence of adsorbed gas is another major feature of shale gas reservoirs.Due to special geological and reservoir characteristics,and compression coefficient change caused by desorption of adsorbed gas has not been taken into account when estimating shale gas reserves with conventional calculating method.So,it is difficult to accurately predict the dynamic reserves of shale gas in that way,but rate transient analysis is more suitable for the estimation of shale gas reserves with low porosity,low permeability and slow pressure buildup.Thus,considering effect of desorption of the adsorbed gas on the compression coefficient and gas deviation factor,this approach introduces the adsorbed gas deviation factor and the compression coefficient to modify rate transient analysis to predict dynamic reserves of shale gas reservoir.Examples show that ignorence of desorption produced by adsorbed gas will lead to lower value of predicting dynamic reserves,but the predicting dynamic reserves of shale gas by modified rate transient analysis is more 20% than that calculated by original calculating method.