Advanced Fluid Characterization of Pauto Complex, Colombia

Abstract

AbstractThis paper presents a detailed fluid characterization study for a group of compartmentalized gas condensate & volatile oil reservoirs making up the Pauto Complex. Fluid oil-gas ratios range from 30 to 350 bbl/MMscf, producing from depths of 12,000–16,000 ft, with estimated IGIP>1 Tcf and significant oil/condensate resources.A single equation of state (EOS) was developed to describe the complex phase and volumetric behaviour of eight reservoir fluids undergoing depletion. The EOS also describes accurately the vaporization of retrograde condensate from one of the richer reservoir fluids when contacted by a leaner hydrocarbon gas.Years of experience in this thrust-belt basin have consistently demonstrated that the quality of fluids samples, PVT test design, lab-data QC, EOS tuning, and fluid initialization are essential to understand the hydrocarbon systems, reservoir compartmentalization, and recovery mechanisms. We show how integration of fluid characterization assists in the evaluation of depletion versus gas-injection strategies, development decisions, and ongoing reservoir management.The methodology used in this study has general application to PVT data acquisition and developing fluid characterizations exhibiting complex phase behaviour. We also provide standardized methods to QC the thermodynamic consistency of an EOS model, particularly when binary interaction parameters (BIPs) are used extensively.A single EOS model was developed successfully for describing the phase and volumetric behaviour of a wide range of fluids undergoing depletion and vaporization. This was achieved by modifying heavy-component properties, but more importantly, modifying BIPs extensively; these BIP modifications were possible only because considerable equilibrium compositional data was available.We believe this paper is significant as a proven case history. With the PVT data provided in our paper, the same problem can be used to test other fluid characterization methodologies and serve as a complex phase behaviour benchmark.