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 non-recoverable 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-gas-expansion 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.
"Anaco Gas?? is compounded by two major areas: "Area Mayor de Anaco??, with mostly volatile and Gas condensate bearing sands, and "Area Mayor de Oficina??, with medium to light hydrocarbon sands. As can be seen in Figure Nº 1, Santa Rosa field is part of the "Area Mayor de Anaco??, and is also one of the main areas of the asset in terms of gas remaining reserves. Typical stratigraphic column is 10.000 feet width, distributed among 150 hydrocarbon sands (Figure Nº 2). These sands are mostly associated to gas condensate production with relatively small API gradients both laterally and vertically. Most of these reservoirs are in advanced state of depletion. As pressure drops within the reservoir, a significant volume of unrecoverable liquid hydrocarbon is gradually left behind, mainly given by phase migration and saturation gradient related damage mechanisms which in turn promote a considerable reduction in productivity to gas mainly in the near wellbore region.
Efforts are being undertaken by PDVSA to increase final recovery of liquid hydrocarbon by Improved Condensate Recovery (ICR) techniques. A pilot ICR project is being developed in the Santa Rosa Field, VEE3 Sands, based on the experimental findings, as well as on the availability of flue gas from both upstream and downstream processes.