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.
Massive hydraulic fracturing (MHF) stimulation treatments are extensively used in tight reservoirs to boost the reservoir performance. A good fractured well surveillance is essential for optimal reservoir exploitation and long-term strategic plan development. Several flow regimes are observed in fractured wells. One of the responsibilities of the well test analyst is to use the appropriate tools to predict the type of flow regime that may develop in the fracture around the wellbore.
Unfortunately, however, some of the flow regimes, especially those pertaining to early well test time such as fracture linear or bilinear flow, may often be masked by wellbore storage effects. Furthermore, sometimes due to technical and/or economical restrictions, the well test analyst may be forced to terminate the test before observing the pseudo-radial flow and/or the pseudosteady state flow regimes; thus, valuable information may be lost due to these difficulties.
Over the years, numerous papers describing the behavior of fluid flow around vertically fractured wells were published. Several methods were proposed for well test analysis of fractured wells. The presented techniques were based on a variety of numerical(1–6) and semi-analytical(7–13) solutions for both finite and infinite fracture conductivity.
Prats(7) and Prats et al. (8) studied the effects of infinite capacity vertical fractures on well performance. Prats(7) examined the flow of incompressible fluids, whereas, Prats et al. (8) inspected the flow of compressible fluids and presented solutions for wells producing at either constant rate or constant bottomhole pressure.
Russell and Truitt(1) pioneered application of techniques based on the assumption of pseudo-radial flow in infinite conductivity fractured wells. They tabulated their numerical results in terms of dimensionless pressure drop as a function of time and fracture half-length.
