In addition to fluid samples, formation testers provide undisturbed formation pressure (p*), as well as mobility and compressibility of formation fluids, essential for estimating initial hydrocarbon in place and recovery efficiency.
Formation tests provide in situ measured permeability and permeability profiles. Recent advancements have been reported in interpretation of pressure test data on liquid saturated formations. For gas formation, however, both compressibility and viscosity are strong functions of pressure; therefore, they are variables during the test. Appreciable temperature change is also observed during gas formation testing. Large gas compressibility and much smaller gas viscosity complicate the analysis. Moreover, gas flow is complicated by non-Darcy flow effects.
In this study, the Gas Formation Rate Analysis (GFRA) technique is developed to analyze gas pressure tests. We calculated gas pseudo-potentials and analyzed variation of pseudo-potential versus formation rate during a formation test by utilizing the geometric factor concept. Forchheimer's equation has replaced Darcy's equation to study non-Darcy flow effects.
The technique is applied to a field test, from which mobility is obtained. The results of the technique are verified by history matching a field test with a 3-D near wellbore simulator, developed for gas formation testing modified for non Darcy flow effects.