Similarity-based, semi-analytical assessment of capillary pressure effects in very tight, liquid-rich gas plays during early-transient multiphase analysis

Abstract

In state-of-the-art production data analysis (PDA) methodologies applied to multiphase flow, capillary pressure is typically neglected in order to enable analytical treatment. However, neglecting the amplified role of capillary pressure in multiphase flow in unconventional formations may generate misleading analysis results during production forecasts and reserve estimations. This work proposes a similarity-based, semi-analytical model eminently applicable to rate transient analysis of unconventional multiphase systems that fully considers the capillary pressure effect. The similarity-based method is developed by solving the governing equations applicable for multiphase flow in early-transient multiphase systems simultaneously, highlighting the effect of capillary pressure not only as an additional pressure gradient for flow but also on fluid PVT properties and hence mobilities and accumulation terms. To arrive at the proposed semi-analytical solution, we apply the similarity method or Boltzmann transformation to the governing system of PDEs, and the resulting system of ODEs is solved simultaneously for pressure and saturation via a shooting method coupled with Runge-Kutta integration. The validity of the series of proposed similarity-based semi-analytical solutions that capture capillary pressure effects is verified by discussing a number of cases studies and comparison against full-scale numerical simulation data.