Well test analysis of finite-conductivity fractured wells producing at constant bottomhole pressure

Abstract

Conventional pressure buildup and drawdown tests are generally influenced by wellbore storage effects. These effects may dominate the early well test data prohibiting good formation characterization of the area surrounding the wellbore. One of the advantages of constant bottomhole pressure tests is that they are immune to these adverse effects. Constant pressure test data can be used with confidence to provide good description of the formation around the wellbore in addition to full-scale reservoir interpretation. This paper presents an analysis technique for finite conductivity fractured wells producing at constant bottomhole pressure from closed reservoirs. The reciprocal rate and reciprocal rate derivative data are directly used to determine the fracture and reservoir parameters without recoursing to type curve matching. All the dominant flow regimes such as early time bilinear, pseudo-radial, and boundary-dominated flow are analyzed using log–log plots of the reciprocal rate and reciprocal rate derivative data. The slopes of the straight lines of the different flow regimes are very distinct and are used to determine various reservoir and fracture parameters such as fracture conductivity, reservoir permeability, skin factor, drainage area, and shape factor. Furthermore, a 0.65 slope straight line equation describing the transition between the infinite acting pseudo-radial and the boundary-dominated flow period in rectangular systems is presented. It is shown in the paper that 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. It is also illustrated that 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 illustrating the methodology of the proposed technique for the analysis of bilinear, pseudo-radial, and boundary-dominated flow regimes is described. The applicability of the method is illustrated using two simulated cases.