A Multistage Approach to IOR/EOR Screening and Potential Evaluation

This paper presents an evaluation study and some latest advances in a multi-stage approach to selection of EOR strategies. The essence of a multi-stage approach is in combination of first-order screening based on ranges for critical oil parameters, statistical data from the world wide database, analytical modelling of IOR/EOR process and economic / risk evaluation.

Screening and analytical methods are often used for fast preliminary evaluations of various EOR scenarios. Advantages of this approach are its speed, relatively small amount of data necessary to estimate the recovery of a particular EOR technique and a dispersion free analytical solution. Simplified representation of the reservoir used in analytical simulation aids in understanding dominating effects and forces and may be used to verify numerical results. The approach is viable and practical when a large number of reservoirs are to be screened for EOR applicability or when a decision over a new asset with limited field data is to be made.

This paper presents new database and improvements in cluster analysis used for estimation of recovery factor. We present a new flexible methodology allowing adding or removing database entries followed up by re-clusterisation and finally cluster-analysis based evaluation of the recovery factor.

A new improved methodology to evaluate performance of the WAG injection is discussed. A three phase compositional path (based on realistic relative permeabilities and rock properties) for each simulation layer is used to determine residual oil saturation to WAG. This value is later on used in analytical evaluation of WAG performance.

Economical evaluation would be integrated into the tool allowing performing economical analysis based on the analytical production profiles calculated within the tool or external data. The economic evaluation may be carried out in "simplified" or "advanced" mode. Advanced mode allows more detalization in specifying costs, while simplified model allows for faster economical evaluation when in-depth economical evaluation is not possible.

Finally a case study of an actual reservoir is presented illustrating how the "EOR compass" could be used in real life situations. The field case presented illustrates screening a new asset as a gas injection candidate. The field in study was taken through a three stage technical evaluation looking at applicability of key development strategies, comparing to the available field cases in the world and finally performing a sensitivity study using an analytical layered model.