Case Study of CO2 Injection to Enhance Oil Recovery into the Transition Zone of a Tight Carbonate Reservoir

Abstract

Abstract This paper presents a case of study of carbon dioxide (CO2) injection into the Transition Zone (TZ) of a heterogeneous, low dipping and tight carbonate oil reservoir. In such reservoir, a relatively thick TZ is expected to contain 30% of the oil in place that would not be commercially feasible to target by water flood. Therefore, the development of this area by Enhanced Oil Recovery (EOR) methods offers a valuable source of oil production. CO2 injection into oil reservoirs is well known as an efficient EOR process as well as one of the promising technologies for reducing greenhouse gas emissions. This study was conducted with the objective to enhance oil recovery in the TZ and also to utilize anthropogenic CO2 as an effective substitute for hydrocarbon (HC) gas injection. In order to define the optimum production strategy to maximize oil recovery, compositional reservoir simulation models were developed and utilized. The effects of several flood design parameters on the efficiency of the process were evaluated, such as: the number of wells and well patterns, well designs, injection schemes, injection and production rates, etc. This paper describes primarily the modeling and flow simulation process developed and utilized for the design of the first commercial CO2 EOR project in the Middle East region to become operational in 2016. The modeling workflow incorporates several important steps from 1-D simulation model to large scale complex compositional simulation models with geological high-resolution grids. The simulation work is supported by a comprehensive and reliable experimental data such as PVT, swelling tests, slim tube and core flood displacement experiments. Important operational experience, understanding of CO2 migration within multiple sub-zone and lessons learned from the CO2-EOR pilot previously conducted in the same field2 are used to reduce technical and commercial risks. An extensive reservoir monitoring plan has been developed to further improve the understanding of reservoir performance, calibrate the models and optimize the CO2 flood. This paper concludes with an assessment of the potential benefits of CO2 injection in the TZ that opens additional development opportunities in other fields.