Analysis of layered gas reservoir performance using a semi-analytical solution for rate and pressure behavior

This dissertation presents the development of a new analysis and modeling technique for layered gas reservoir performance where production is commingled at a constant wellbore pressure. This technique is based on a semi-analytical solution that couples an approximate form of the stabilized flow equation with the rigorous gas material balance equation for a dry gas reservoir.; The specific tasks achieved in this work include the following: (1) The development of a semi-analytical solution for the depletion (i.e. , boundary-dominated flow) performance of wells produced at a common production pressure in a layered gas reservoir. This scenario is that of a “layered, no crossflow” case, and as such, we duplicate (and extend) the numerical simulations given by Fetkovich, et al. using our semi-analytical approach (as a validation) of our solution. (2) The development of new p/z analysis techniques that can be used not only to estimate gas reserves (G) on a “per well” basis, but also to estimate the original gas-in-place (G_i), the permeability ratio (k₁ /k₂), reservoir layer volumes, and the effect of drawdown (i.e., the magnitude of the wellbore flowing pressure). This new p/z analysis technique for multilayer reservoir behavior is substantially different than the conventional p/z straight line technique (i.e., the single layer solution), and it requires a “dynamic” matching sequence to correlate the model to the field data. We have applied this new technique for the analysis of layered gas reservoir performance data taken from the Hugoton Gas Field, Kansas (USA). As part of this analysis we also provide validation using a commercial numerical simulation program for each case. (3) The generation of new production performance type curves for layered gas reservoirs. These type curves are generated based on gas flow rate and time models which are given in dimensionless format. We can apply these new type curves to estimate the productivity index (J_g ) and the original-gas-in-place (G_i) for both “parent” and “infill” wells. We have also applied the type curve techniques to field data taken from the Hugoton Gas Field, Kansas (USA). We have validated these type curves using synthetic data generated by a commercial numerical simulation program.