A Specific Way of Assessing Target Recovery Factor (Chalk Oil Fields)

An important aspect of oil field management is to compare a field’s recovery performance with analogues to assess whether the field is being fully exploited and economic recovery is being maximized. However, this can be difficult when there are many differences in basic parameters that might impact recovery potential. A number of qualitative methods have previously been developed but they tend to be too generic to allow meaningful recovery potential analysis. The objective of this study has been to develop a tool to assess and understand the recovery performance of offshore Danish fields in relation to world analogues. This can be done meaningfully in a semi-quantitative fashion by limiting the analysis to chalks and by calibrating, where practical, the impact of key parameters with reservoir simulation analysis. The main steps in the study were to establish the principal geological and dynamic drivers determining recovery factors in chalks; build a “calibrated” recovery factor potential model and apply it to worldwide chalk fields, using published data. The results show that the Danish chalk fields become progressively more complex going from the Tor formations, which have been successfully waterflooded; to the Ekofisk, where there remains technical potential for implementing waterflooding; to the Lower Cretaceous where waterflooding recoveries are theoretically comparable to depletion but due to complexity and expense are unlikely to be attractive. A number of reservoir management activities have been identified to increase recoveries. Overall the Danish field recoveries compare favourably with world analogues. Operators in the Danish sector are likely leaders in exploiting more complex and particularly lower permeability chalk fields. The Recovery Factor Potential tool developed in this study allows chalk field performance to be compared in a more quantitative manner, making it easier to understand causes of underperformance and to identify reservoir management activities to increase recovery.