A New Method to Calculate the Recoverable Reserves and Recovery Ratio of Shale Gas Reservoir

摘要

At present, the most commonly used method to calculate recoverable reserves of shale gas reservoirs is the production decline curve method, which is only applicable to the production wells with decreasing production. For the production wells with constant productions, the material balance method could be used to calculate the recoverable reserves, but it does not consider the particularity of shale gas reservoirs. Under this circumstance, this paper deduces a new calibration method for recoverable reserves of shale gas reservoirs with double porosity medium. The method is based on the material balance equation, which has a wide application range. The method cannot only calculate the recoverable reserves and recoveries of free gas in fractures, but also calculate recoverable reserves and recoveries of free gas and adsorbed gas in the matrix. The calculated results show that the free gas in the shale gas reservoir is mainly in the fractures. The recovery of the free gas in the fractures is relatively high and the recovery of the free gas and adsorbent gas in the matrix is rather low. Gas reservoir recovery and recoverable reserves are more sensitive to abandonment pressure, therefore, in the production process, the reduction of the abandonment pressure of gas reservoir should be attempted. The matrix porosity, the adsorption phase density and the crack compression coefficient have a greater effect on the recovery rate. And the study of these parameters needs to be strengthened in order to obtain more accurate parameters.