Case Study of Heavy-Oil Fluid Characterization for Gas EOR Experiments: Main Challenges

Abstract

Abstract Staatsolie conducted several screening studies in the past decade to explore the potential of enhanced oil recovery (EOR) for its heavy oil (16-17° API) fields in Suriname. The latest study that was performed in 2011, indicated that water and carbon dioxide (CO2) or water and nitrogen (N2) injection could be a highly efficient method to extend the life of the fields beyond primary recovery. To validate this conclusion an area of the Tambaredjo heavy oil field was selected for a feasibility study comprising laboratory tests, reservoir simulation studies and ultimately a field pilot trial. This paper presents the results of the laboratory study of the fluid properties of the selected study area. Several oil and gas samples of two wells situated in the study area were collected at the wellhead and at the Multi Phase Flow Meter (MPFM). After quality control, the composition and the physical properties of the samples were determined. Various pairs of oil and gas samples were then recombined based either on assumed bubble point pressure or gas-to-oil ratio (GOR) in an attempt to produce mixtures representing the reservoir fluids. Two recombined samples were subsequently selected based on a comparison with historical data for PVT analysis and swelling study with carbon dioxide and nitrogen. The PVT behavior was found to be qualitatively similar to that of the samples examined in the past except for the viscosity which seems to have increased over a period of ten years of depletion of the reservoir in this part of the field. Most likely this can be attributed to vaporization of the lighter components of the crude oil. CO2 readily dissolved in the heavy crude oil which led to substantial reductions of oil viscosity while N2 could hardly be dissolved in the oil. The challenges met during sampling, recombination of the samples and the PVT analyses will be discussed.