Characterization of Early-Time (Clean-Up) Performance for a Well With a Vertical Fracture Producing at Constant Pressure
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© 2017, Unconventional Resources Technology Conference (URTeC). An anomalous flowrate feature (often a "hump" or even a "spike") is characteristically observed at early-times during flowback performance in multi-fractured horizontal wells (MFHW) completed in ultra-low permeability (shale) reservoirs prior to the onset of a characteristic reservoir flow regime (i.e., linear or bilinear flow). The flowrate feature tends to occur in all fluid phases and this feature is thought to be attributed to the "clean-up" behavior following well stimulation and/or the phase behavior of the fluid as it flows along the well path. The guiding principle of this work is that this anomalous flowrate feature can be represented by decaying skin effects, a changing wellbore storage effect, or a combination of both decaying skin effects and changing wellbore storage effects. The goal of this work is to provide a proof-of-concept which considers the simplified case of a vertical well with a single vertical fracture to develop a series of time-dependent skin and wellbore storage models that can effectively be used to characterize the early-time flowrate behavior observed in practice. For this study, we forced a constant wellbore flowing pressure constraint, and while we recognize that this constraint is not truly met in practice, we believe that this approach can serve as a base model for diagnostics/interpretative analyses. Based on the work developed by Fair (1981) and Larsen and Kviljo (1990), our procedure is to couple a series of time-dependent wellbore storage and skin effect models with a set of "power law" reservoir flow models (i.e., linear flow, bilinear flow and a generalized power-law flow model). Specifically, we combine the time-dependent wellbore storage and skin effect models with the constant rate solution reservoir flow models, then apply the convolution integral to produce the constant pressure condition - all in the Laplace domain. In order to generate various scenarios of production performance, we use the Gaver-Wynn-Rho Algorithm implemented in Mathematica to numerically invert the Laplace domain solutions into the real time domain. A generalized workflow is provided to demonstrate the addition of time-dependent wellbore storage and skin effects to any prescribed reservoir model. Using the various wellbore storage and skin time-dependent models proposed in this work, we observe that each of these models, individually and in combination, provide behavior indicative of early-time flowrates observed in the field. In short, we demonstrate that each time-dependent model has unique characteristics, which could, in concept, allow for characterization of flow behavior in the fracture prior to the onset of an undistorted "reservoir" flow geometry (i.e., formation linear or bilinear flow).
author list (cited authors)
Wiewiorowski, N., Valdes-Peres, A., & Blasingame, T.
complete list of authors
Wiewiorowski, Nicholas||Valdes-Peres, Alex||Blasingame, Tom