DefinePK

Abstract

Currently, the oil industry is focused on the exploitation of unconventional reservoirs. Wells in such unconventional resources as gas shale formations have to be hydraulically fractured for commercial production since the permeability is very low to ultralow reaching values in the order of nanodarcies. Also, gas shale wells are normally tested by recording the flow rate versus time readings under constant pressure conditions so an analysis of the reciprocal rate and reciprocal rate derivative following the TDS philosophy is presented for two cases in which the network of microfractures around the main fracture system provides an improvement of the permeability in such zone and one case in which the permeability is considered to be uniform. These three cases have been dealt in the literature with decline-curve analysis and the identification of the permeability model, dealt as a transition period, is conducted by type-curve matching which basically consists of a trial-and-error procedure. Here, we found that the application of the reciprocal rate derivative allows to easily identify the type of permeability model to be used: uniform, linear and exponential since the before-called transition period is shown on the derivative curve as a specific behavior which has been arbitrarily called “multilinear flow regime” displaying a slope of either 0.66 or 0.61 on the reciprocal rate derivative curve for the exponential and linear variation models, respectively. The extension of the TDS technique allows for the characterization of well test data so permeability, fracture length, skin factor and reservoir length are estimated and successfully verified by their application to synthetic and field examples.