Published by the DTI Oil & Gas Directorate for the reservoir engineering and IOR community in the UK.
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Screening Model Provides Insight into Field Problems and Identifies IOR Opportunities.

AEA Technology was asked to assess a mature North African sandstone reservoir for miscible flooding. The field had been producing for over 30 years and had received sporadic waterflooding into the oil zone during this time. Historical field behaviour was not well understood and a particular puzzle was the discovery of a flushed zone of formation water in crestal wells updip of historical injector positions. The ingress of formation water was much larger than would have been predicted from permeability contrasts alone.

The geology of the field was reasonably straightforward so we were able to use a simplified layer cake model of the field. "Performance Indicator" screening [1] indicated that the waterflood had been viscous dominated and that a miscible gas flood was technically promising. On the basis of this information "Rapid Simulation" [1] was used to build a representative detailed sector of the field. It became clear that a combination of low dip, partial pressure barriers and low injection rates were likely to be responsible for the observed waterflood behaviour.

Having built a credible model of the historical performance we felt confident that the level of detail in the model would be sufficient for us to assess miscible gas flooding. "Rapid Simulation" allowed different WAG ratios and sensitivities to field parameters to be quickly examined. Scoping level profiles and gas utilisation parameters were produced that were then examined for economic viability.

This study demonstrates the benefits of using a systematic approach for IOR assessments. The whole study was completed in less than 3 weeks, providing large savings over conventional full field assessments. The historical field behaviour was satisfactorily explained, viable IOR techniques were identified and ranked, and critical project parameters identified. The study will now be used to provide input for detailed appraisal of the selected miscible flood scheme.

1. Thompson M A. Goodyear S G. Identifying Improved Oil Recovery Potential: A New Systematic Risk Management Approach. SPE 72103.

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