Assessment of Field Scale Commercial Development for Miscible EOR in a Giant Offshore Carbonate Reservoir

Willingham, Thomas W. (ZADCO) | Kohata, Akihiro (ZADCO) | Al Sowaidi, Alunood (ZADCO) | Martin, John D. (ZADCO) | Irwin, Drew D. (ZADCO)



In this work we present the evaluation of field scale commercial miscible EOR for a giant offshore carbonate reservoir. The current assessment leverages the prior multi-year evaluation assessing the attractiveness (‘do-ability’) and prize for miscible EOR within each geologic area and reservoir within the field.

Two geologic areas, the "heterogeneous" and "homogeneous" geologic regions of the Crestal area in the largest reservoir were identified as the primary targets for field scale miscible EOR based on the prior multi-year assessment and are the focus of the current assessment. Commercial field-scale miscible development is predicated on a 1-to-1 line drive waterflood with 1km spaced extended reach horizontals with 10,000 ft completions and 500m spaced infills in the more heterogeneous area of the field.

Given the offshore environment, base development utilizes four artificial islands which support facilities for field development and serve as drilling centers. Commercial development with miscible EOR will be implemented in a ‘phased’ (staged) approach where the initial developments will be from the Central Island in the late 2030s followed in succession by the South Island in the early 2040s and North Island in the 2050s.

This assessment uses a novel phased approach where a ‘Tapered WAG’ scheme is used. By utilizing a phased (‘staged’) approach, multiple development concepts can be evaluated expediently. In this work we (i) show an efficient field assessment process for miscible EOR, (ii) illustrate how subsequent patterns can be brought on-line over time as part of a Tapered WAG process and (iii) demonstrate the importance of commercial assessment as part of field development planning and pilot assessment.

The full field assessments included here allows multiple development strategies to be assessed expediently and facilitates the selection of an injection solvent (hydrocarbon gas or CO2). Full field economics have been completed and hydrocarbon gas has been identified as the target solvent. Hydrocarbon gas has the benefit of being commercially attractive and is compatible with existing facilities. Currently two pilots are in preparation to assess the incremental recovery beyond waterflood and assess the commerciality of miscible EOR in a giant offshore carbonate reservoir. Key learnings in this paper include (i) an efficient methodology to assess phased field development for miscible EOR, (ii) incremental recovery of miscible EOR beyond waterflood, (iii) metallurgy and facility requirements for the two solvent schemes and (iv) a preliminary assessment of field scale commerciality including economics for the two solvents, hydrocarbon gas and CO2.