Evaluating gas injection performance in R2U YS-32 reservoir of Central Yopales oil field by an integrated reservoir characterization approach.

Gas injection is an efficient oil recovery technique if it is properly design, executed and surveyed. The injection of gas into a reservoir can be designed for pressure maintenance or gas flooding for oil displacement. This article presents the evaluation of the Gas Injection Project for Pressure Maintenance in R2U YS-32 reservoir of Central Yopales Oil Field through a reservoir characterization study that consisted of four phases: Data Compilation and Validation, Reservoir Static Model, Reservoir Dynamic Model and Gas Injection Performance Evaluation. The first phase was directed to compilate and validates the data available, which allowed detecting the additional information needs and establishing a reliable database for the following phases of the study. The Static Model consisted in geologically characterizing the reservoir using a conventional methodology. This allowed validating and/or reinterpreting the main stratigraphic and structural characteristics of the R2U YS-32 reservoir, thus determining the communication between the R2U YS-32 and R2 YS-68 reservoirs. Now they represent a single reservoir called R2U YS-32. Through static modeling, original oil in place (OOIP) of 33.35 MMbbl was volumetrically estimated. The Dynamic Model comprised the monitoring of production, injection, and pressure of the reservoir. This phase was developed, in large part, parallel to the Static Model phase. Through dynamic modeling, it was determined that the reservoir was initially saturated at a pressure of 1490 psi with a bubble pressure of 1617 psi and a gas cap size of m = 0.1255. It was also determined that the main mechanisms of production during the natural depletion period were the expansion of fluids and water intrusion, while gasinjection is the main mechanism during the secondary recovery. In addition, in this phase the volumetric OOIP was validated satisfactorily by material balance, being estimated at 33.33 MMbbl. Results showed that the gas injection did not achieved the expected results, basically because it did not manage to maintain reservoir pressure, minimize the advance of the aquifer, nor evenly sweep the oil towards the producing wells. This was mainly due to that during the first years of the gas injection, a large part of this was produced through the YS-68 well, which is connected to the reservoir's gas cap through a non-sealing fault. Additionally, the required gas volumes were not injected during the rest of the injection period. Since the reservoir has not produced since 2002, it is suggested to analyze different alternatives scenarios to reactivate the reservoir oil production including techniques like cyclic water injection or dump flooding that had been studied and planed in reservoirs/fields close to the Yopales field. [ABSTRACT FROM AUTHOR]