Enhanced oil recovery (EOR) using CO2 is an important recovery process that can increase recoverable hydrocarbons and sequester CO2 simultaneously. For light oils, CO2 injection is particularly interesting and is considered a win-win strategy that sequesters CO2 and provides additional oil reserves at the same time.
Saudi Aramco has designed and implemented the first CO2-EOR demonstration project in one of the fields. It is worth mentioning that while Saudi Aramco does not require EOR oil for decades to come, this project is being pursued primarily to demonstrate the feasibility of sequestering CO2 through EOR in the Kingdom and using it as grounds to test new monitoring and surveillance (M&S) techniques. The project consists of two components: the actual EOR project in a small part of a field, and the CO2 capture plant. An overall plan covering laboratory and research studies, reservoir modeling and simulation, monitoring and surveillance, construction of a CO2 capture facility, project implementation and evaluation will be presented for this first demonstration project.
The project uses 40 million standard cubic feet per day (MMscf/d) of CO2 that is being captured and processed from an existing facility and piped about 85 km to the field location. An innovative progressive infill line drive has been implemented to take advantage of the east-west fluxes in the field. This includes a row of four injectors and four producers, and another set of observations wells for monitoring and surveillance. The CO2 is being injected in a water-alternating-gas (WAG) mode. An elaborate monitoring and surveillance program has been established and currently being implemented to evaluate the performance of the project. It includes the deployment of several new technologies including seismic, inter-well tracers, gravity, geochemical sampling and analyses that will be discussed in the paper.
The main objectives of the demonstration project are estimation of sequestered CO2, determination of incremental oil recovery, addressing the risks and uncertainties involved, including migration of CO2 within the reservoir and operational concerns. It is estimated that up to ~40% of the injected CO2 will be sequestered permanently in the reservoir.