Comparison of techniques which use the DST flow period data for evaluation of reservoir parameters

Abstract

This paper presents a comparison of techniques utilizing DST flow period data for calculation of permeability and skin. Results obtained using the commonly accepted "type curve" method and the technique presented in Szpunar (2001) are summarized. It has been demonstrated that the results of each of these methods do not differ much. Advantages and disadvantages of each technique are discussed. Our new method presented in Szpunar (2001) and developed by Szpunar and Budak (2012) may also be used for interpretation of downhole pressure or water level behavior in coal bed methane wells and water wells which do not flow to the surface after the pressure disturbance is introduced by addition or removal of water from the well. Apart from reservoir permeability and skin, the presented method enables calculation of permeability of the wellbore zone and depth of impaired/improved permeability, providing the pressure drop within the DST conduit is negligible when compared to hydrostatic pressure exerted upon reservoir by a column of liquid moving up the well. The commonly known "type curve" method does not offer such possibility. According to the authors, the "type curve" methods-in spite of their theoretical merits-provide results which are uncertain because they require adaptation of the measured curve to one of theoretical curves, the shapes of which are very similar. Summarizing-there is an acceptable agreement between permeability calculated using each of the methods discussed, but one should not expect that permeability calculated using each of the methods to be identical.