To optimize oil recovery from Vaca Muerta (°API 40, GOR 617 scf/stb), lab tests were conducted to assess miscible gas injection. This unconventional formation with average initial pressures of 8500 psia and fluid bubble pressures between 1800 and 3200 psia, shows a significative oil decline. The formation's low transmissibility suggests that Huff and Puff gas injection is the best recovery option. This method not only reduces the decline rate but also improves wellbore flow. This work considers from PVT tests of the fluid to production forecasts by numerical simulation. The findings will be key to a pilot design.
PVT tests were conducted to represent fluid behavior under reservoir conditions. Swelling tests were also performed to analyze the mixtures between the original fluid and injected gas, and two types of gas were studied: dry gas (from the Turboexpander plant outlet) and rich gas (primary separator). During the swelling tests, a known gas was injected into the original fluid at bubble pressure and reservoir temperature, increasing the pressure until total miscibility was achieved. This process was repeated with new gas fractions, determining properties and saturation pressures for each mixture. The study and the pilot test were conducted in the Agua del Cajón Area, in central-eastern Neuquén.
The previously detailed laboratory tests served as a basis for characterizing the fluids and adjusting the state equation models that simulate their thermodynamic behavior. Once defined, several runs were carried out in the numerical simulator to optimize oil recovery efficacy through gas injection in the reservoir, considering various gas injection compositions (dry or rich gas), for the pilot well implementation design.
The behavior of the wells with the new fluids to be produced was also evaluated, as well as the separation conditions for each injection alternative, seeking to optimize operating conditions to maximize oil recovery.
Extremely interesting results were obtained showing an increase in RF and observing the change in the original fluid's behavior from light black oil to a "near critical" fluid after gas injection. This promotes the application of this technique to increase associated production and optimize the development of this type of reserves.
A pilot will be designed to be implemented in a current well in the area to evaluate performance and model adjustment.
