Abstract
Bachaquero-01 is one of the largest offshore, heavy oil (12 °API) reservoirs in Maracaibo Lake basin. It is a mature field with a long time production history and a large number of steam injection cycles. Due to these conditions, a low well productivity and a high water saturation near wellbore are the order of the day, causing high operating cost and reducing expectation in oil recovery. In addition, steam generation units are facing the shortage of natural gas. To solve issues before mentioned, it is being planning to increase the reservoir production through implementation of a more adaptable enhanced oil recovery method according to the current field operation conditions.
This paper describes the development of a novel analytical model for a huff & puff CO2 injection as a potential method of oil recovery for Bachaquero-01 reservoir.
Fundamentals of the proposed model, represented by a global mass balance applied to the injector-producer well in a inverted seven-spot pattern, were based on simultaneous solution of several differential equations, as in the case of heat energy balance for determining the reservoir's temperature transient, evaluated by Marx and Langenheim's model. In addition, the oil flow rate was defined by an adaptation of Boberg and Lantz's model. Also, a partial material balance equation based on the Fick's law of gas-liquid diffusion, and the diffusivity equation that governs the pressure transient behavior determined by Van Everdingen and Hurst were implemented. Additionally, a full set of correlations for physical properties of oil-CO2 mixing based on Simon and Graue monograms were generated.
The stability of the simultaneous solution of the differential equations system was acceptable. Results showed a production cycle of 4 months was necessary for reach the optimum stimulated diffusion zone with an average production rate using CO2 injection at reservoir temperature (130 °F) of 400 BOPD versus an average production rate by hot CO2 injection (200°F) of 450 BOPD.
