Virtual special issue: Advanced numerical simulation technology enabling the analytical and semi-analytical modelling of natural gas reservoirs (2009–2015)

Abstract

Production decline analysis is a technique where actual production history is modeled with a theoretical relation. The production model could then be used to estimate hydrocarbon in place and reservoir properties just like expensive pressure transient tests. Gas/condensate reservoirs exhibit different thermodynamic and flow behavior and the multi-phase production data of such reservoirs cannot be accurately analyzed using available production models.This study presents a novel analytical model to analyze multi-phase gas/condensate production data in both transient and boundary dominated flow regions for variable bottom-hole pressure/rate conditions. Initial gas-in-place, average reservoir pressure, and drainage area size could be calculated from analysis of boundary dominated flow region data and reservoir permeability and well skin could be calculated from analysis of transient flow region data. The effects of positive coupling and negative inertia are also included in the formulation. The proposed model forms a linear plot and the desired estimates of reservoir properties could be determined simply. To use the transient flow region data in analysis, new dimensionless parameters are introduced and the proposed model is also presented in type curve analysis format.Different fine-grid compositional simulation models are used to validate the proposed method. The effects of reservoir fluid types, relative permeability data, production well survey, and production history mode on the results were evaluated. The model is also evaluated using actual field data. Small error values in all cases (below 5%) show that the proposed method estimates the reservoir properties quite well and it is applicable to field data. Moreover, the developed type curve method is a good tool to diagnose the reservoir flow regime.