Application of the transient rate decline analysis for determining average reservoir pressure in naturally fractured reservoirs

Based on the fracture-pore dual medium model proposed by Warren and Root et al, the solution of the pseudosteady-constant production fractured system by Mavor and Cinco-Ley and the solution of the pseudosteady-constant pressure matrix system by Daprat are extended, and a new method is presented for estimating average reservoir pressure of naturally fractured reservoirs using the transient rate decline analysis. The specific method is taking logarithm of the matrix production equation and fracture production equation to obtain two straight lines; then the slope and intercept of the straight lines are used to determine storage capacity ratio, total storage capacity and reservoir drainage area, and average reservoir pressure at last. Examples show that the new method is easy and practical, and gives result similar to that of the material balance method and direct Tiab synthesis method.