Study On Calculation Method Of Single Well Dynamic Reserves In Shale Gas Reservoir

Shale gas is stored at the reservoir in the form of free gas,adsorbed gas and dissolved gas.Scholars have proved that there is a lot of gas dissolved in kerogen,which is an important way of storing gas.However,the dissolved shale gas in solid kerogen is not taken into account in the previous methods of calculating shale gas reservoir.As a result,previous methods can't calculate shale gas reserves truly and accurately.So in this paper improved calculation methods of shale gas reservoir reserves to calculate shale gas single-well producing reserves are established,considering the volume of the adsorbed phase and the dissolved gas in the solid kerogen.These methods include improved material balance equation for constant volume gas reservoir,improved material balance equation for closed gas reservoir,improved flow material balance equation,improved Palacio method,improved Anderson method,improved Ibrahim method.The production indicator curve can be drawn using the calculated producing reserves,and then the recoverable reserves of shale gas wells will be calculated when the formation pressure reaches the abandonment pressure.In addition,the methods of Arps decline,extended exponential decline,Doung production decline,power-law exponential law decline are used to predict the economically recoverable reserves for production wells in which production has declined.Finally,these methods are combined to develop a set of software by Java which can be used for calculating shale gas well dynamic reserves.Four typical wells are used for example calculations.Through comparing the results of the previous calculation of the producing reserves with the improved methods,it can be seen that the reserves of the free gas and the adsorbed gas will reduce under current production data when considering the adsorption phase volume and the dissolved shale gas in the solid kerogen.The improved calculation methods of the producing reserves can also be used to test the average pressure of the formation,which is very practical to low porosity and low permeability shale gas reservoirs.What's more,the application areas are more extensive by using the improved production index curve to test recoverable reserves,which can also be applied to the production wells whose gas flow has reached relatively stable state.Comparing a variety of production declining curves,it can be found that the power law decline model,extended exponential decline model and Doung production decline curves fit with the production history of shale gas wells.However,the power law decline model does not fit well in early period and the Doung production decline method takes too long to reach the time limit of economic production.The satisfactory results of prediction can be obtained only by extended exponential decline method.Finally,after the instance test of the software,it can be found that the dynamic reserve calculation software programmed by Java is easy to operate and the result is accurate.