A Novel Improved Condensate-Recovery Method by Cyclic Supercritical CO2 Injection

摘要

In the Eastern Venezuela gas assets, mid to long term planning business portfolio considers an increasing gas production potential and recoverable reserves under secondary or improved recovery methods. Most gas reservoirs are originally under or near saturation pressure. Native thermodynamic conditions along with typical production practices favor in-situ liquid condensation, leaving behind considerable nonrecoverable liquid hydrocarbons. This liquid condensation is triggered by unfavorable pressure gradients developed under natural production as reservoir static pressure drops below saturation pressure, primarily in the near wellbore region. In addition, as gas expands due to the adiabatic real-gasexpansion Joule-Thompson effect, a reduction in the surrounding temperature is also expected. This effect, in turn, often favors a sharp reduction in the relative permeability to gas when “In Situ” liquid condensation takes place at interstitial level hence promoting a drastic decay in the gas productivity. Consequently, a considerable amount of liquid hydrocarbon is left behind in the reservoirs. Based on the nature of the experimental findings, the availability for flue gas in the Eastern Venezuelan region, and the environmental concerns, a breakthrough improved Condensate Recovery (ICR) project is being considered by “Cyclic Supercritical CO2 Injection”. The cyclic nature of the process combined with the favorable equivalent density for the CO2 at reservoir condition is expected to positively impact thermal diffusion and accelerated mass transfer processes respectively mainly in the near wellbore region. In this project, pilot temperatures are expected to be in the range of 350 to 450 oF. A combined effort to integrate experimental results into a numerical model was undertaken. A number of laboratory tests were programmed to typify both fluid and rock interactions and also to characterize the thermodynamic profile for the CO2 and In Situ live fluid. The interaction coefficients of the equation of state (EOS) for the enhanced process were experimentally characterized reproducing the multiple contact events between the in situ liquid hydrocarbon and the foreign fluid (CO2) as a function of temperature. Expected sweep efficiencies and residual liquid saturation after multiple contacts with CO2 were experimentally determined via core displacement tests using actual core samples. Soaking time extent was also optimize for energy diffusion purposes. At a second stage, a single well model will be assembled, to numerically reproduce the experimental results, to match primary depletion and to predict enhanced recovery production profile. For field implementation, a pilot area was selected in the Santa Rosa Field belonging to Petroleos de Venezuela assets.