Rate Derivative Analysis of Oil Wells Intercepted by Finite Conductivity Hydraulic Fracture

Abstract

Early time conventional transient pressure test data are generally influenced by wellbore storage effects. These effects prohibit good formation description of the area in the vicinity of the wellbore. One of the advantages of constant bottomhole pressure tests is that they are immune of these effects. This study presents an analysis method for finite conductivity fractured oil wells producing at constant bottomhole pressure from closed systems. The reciprocal rate and reciprocal rate derivative data are used to calculate the fracture and reservoir parameters. Bilinear, pseudo-radial, and pseudosteady state flow regimes are analyzed using log-log plots of the reciprocal rate and reciprocal rate derivative data. The slopes of the straight lines of the various flow regimes are used to determine reservoir and fracture parameters such as fracture conductivity, reservoir permeability, skin factor, drainage area, and shape factor. A 0.65 slope straight-line equation describing the transition between the pseudo-radial and the pseudosteady state periods in rectangular systems is presented. This straight line can be used to either determine the formation permeability in the absence of the pseudo-radial flow, or calculate the drainage area. Moreover, the intersection points of the various straight lines can be used to verify the accuracy of the results obtained from the different flow regimes. A systematic step-by-step procedure showing the methodology of the proposed technique is illustrated using two simulated cases.