A Study of Heavy Oil Solution Gas Drive for Hamaca Field: Depletion Studies and Interpretations

Abstract

Abstract We present results of a systematic study performed to investigate heavy oil solution gas drive process for Hamaca field in Venezuela. The ultimate goal of this study is to provide the data needed for Hamaca reservoir simulation studies. The study included a series of rock and fluid property measurements, and several carefully performed depletion experiments. Supplemental experiments using PVT cells and ideal porous media were also conducted to aid in the analysis of the depletion experiments. For this study, single-phase live oil samples from Hamaca Field were used. Fluid characterization tests were performed, including GOR, viscosity, density, compositional measurements and other PVT experiments. Average properties of the live oil used were GOR of 96 scf/STB, bubble point pressure of 1020 psia at 125 °F and viscosity of 1650 cP at reservoir conditions. In addition, several flow experiments were conducted using the live oil to elucidate so-called "foamy oil" behavior by obtaining rheological data at above and below thermodynamic bubble point. Depletion experiments were conducted at reservoir conditions using field core and oil samples from Hamaca Field. Tests were performed at constant depletion rates from 0.25 psi/hr to 43 psi/hr to cover the flow regimes, which may be occurring at different distances from the wellbore. A CT scanner was used to observe the distribution of gas saturation at various points during the depletion tests. Critical gas saturation values ranged from 8 to 15%. Depletion rate did not have significant effect on the critical gas saturation. Gas-oil relative permeability curves were calculated using a new technique based on effluent density measurements done during the depletion experiment. Calculated gas relative permeability curves appeared to be suppressed, in the range of 10−10 to 10−5.