CO2 injection into oil reservoirs for EOR is well known as one of the most proven and efficient Enhanced Oil Recovery (EOR) processes. The subject study was conducted with the objective of enhancing oil recovery by injecting CO2 into a heterogeneous, low dipping and low permeability carbonate oil reservoir. The required CO2 is captured from a steel plant (Emirates Steel Industry (ESI)) which is part of a large scale carbon capture and injection project. The project entails capturing, dehydrating, compressing, and transporting the CO2 to the oilfields for sequestration and/or EOR processes. The carbon capture from ESI is part of a collaboration (Joint Venture) between ADNOC and MASDAR which will help make CO2 available for potential future EOR operations along with the added benefit of reducing Abu Dhabi's carbon footprint. As part of this initiative, planning of the CO2 EOR process as part of ADNOC's EOR strategy is essential and includes building a phased development CO2 EOR model. The strategy is to breakdown the overall objective into phased developments/projects in order to gain experience in surface and subsurface aspects of CO2 EOR, operations and mitigate risk. The end goal of the phased development is to enhance oil recovery, improve CO2 utilization, and maximize project profitability by implementing more complex operations such as Continuous/WAG CO2 injection, CO2 recycling, and the development of "difficult oil" from flank areas with higher water saturation (transition zone). This paper discusses the benefits and rationale behind building such a phased development model.

A Water-Alternating-Gas (WAG) scheme is a proven enhanced oil recovery (EOR) method. The first WAG project was reported in 1957 and until today more than sixty (60) field experiences can be found in the literature. Most of the published experiences report 5-10% additional oil recovery over waterflood. WAG injection can lead to improved oil recovery by combining better mobility control, improved microscopic displacement, and better sweep efficiency.This study presents a recent field experience where a miscible WAG injection has been designed and implemented with the objective of enhancing oil recovery in a heterogeneous, low dipping, and tight carbonate reservoir. The project has been performed on close-spaced slanted wells and utilizes rich hydrocarbon gas. Since the beginning of the injection, an integrated surveillance program has been applied to determine whether the miscible flood is working efficiently. This program involves observation wells, time-lapse saturation logging, well testing, tracer injection, and i-field technology along with numerical simulation.This paper presents a review of the main findings, issues and lessons learned during eight (8) years of EOR-WAG injection. The paper discusses the project design, the integrated surveillance program and the WAG mechanisms to enhance oil recovery. It also summarizes worldwide WAG experiences based on published field observations.

The initial hydrocarbon (Oil and Gas) in-place represents the asset volume of ADNOC that is required estimation at high accuracy level with minimum uncertainties to avoid any future risks with fields' development plans. Moreover, accurate estimation of the reserves that can be produced during the field life cycle is critical as it is directly impact the CAPEX and OPEX of different field development phases.Fields developments are usually selected based on the techno-economic evaluations of the outcome from the full field simulation studies using representative models. Accordingly, management decision for fields' development is totally dependant on the accuracy of the used simulation models.Worldwide, there are many simulation models successfully demonstrating good history match profiles, nevertheless, several of these models are utilizing unsupported parameters, such as representative capillary pressure and relative permeability curves. In addition to the adverse impact on the predictive reliability, massive convergences problems that are encountered and participating in slowdown the models performance and decreasing accuracy. Subsequently, incorrect Long Term Development Plans "LTDP's" profiles will be generated. Therefore, in order to ensure achieving more representative asset volume estimates, a new procedure has been setup, established and successfully validated through different fields. The main objectives of the new procedure are to enhance model initialization with minimum gap in terms of hydrocarbon-in-place between the static and the dynamic models below the range of 1.0 %, to achieve more accuracy of the expected movable oil and gas with respect to water flooding (Current Development Plan) and future Gas/WAG flooding (LTDP), to eliminate high risk of assessment of modeling the actual gas/water breakthrough timing, recovery factor, sweep efficiency and fields measured matching parameters, and to cut down potential risks of under/over estimating the water/gas influx fronts in the reservoir.Quality match is essential in order to prevent utilization of non-measured parameters such as irreducible water saturation (Swc's), also to eliminate utilization of unproven permeability multipliers. Moreover introducing a new capillary pressures (Pc) designing concept will contribute in reducing convergences problems as well as providing more consistent dynamic model setup (dynamic model rock typing).Based on the results from several simulation studies which were introduced to the new procedure framework, the new procedure managed to demonstrate its capability to design the most reliable capillary pressure profiles. These profiles are essential for simulation models to ensure quality match of lateral and vertical oil and gas distribution in the field which represents the most extremely improvement match achieved when compared with other used method.

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