Abstract

Evaluation of reservoir drive mechanisms is an important part of the field development planning process as it underpins recovery and defines project scope. Optimization of project scope (and resulting CAPEX) and the associated recoverable resource requires understanding of the natural reservoir energy and contribution of Improved Oil Recovery techniques such as water injection. This paper describes the evaluation of compaction drive for deep water fields for a development screening study. Pore volume compressibility has been characterized based on field burial depth, core analysis, tidal analysis and log data. Integration of this data provides a valuable knowledge base for regional screening and to bridge data gaps by enabling the use of more readily available log data for fields where a specific core laboratory test is not available.

The primary source of information for pore volume compressibility is the laboratory testing on core. For the three fields included in the development screening study, only two have core testing results available for PV compressibility. A comprehensive analysis is undertaken to verify the core test results and to deduce the expected range of PV compressibility for the third field. The connected volume of the field (oil and aquifer zones) is an essential consideration for compaction drive. This is illustrated with material balance analyses of fields with limited vs significant aquifer support and implications on recoverable resource.

Uniaxial tests on core samples are used to quantify static PV compressibility but these measurements are not available for all reservoirs. The effectiveness of establishing analogue trends and correlations for the characterization of PV compressibility is also demonstrated. Burial depth can be an initial indicator but may not be valid in all cases and an example of a geologically uplifted field is considered to help illustrate this. Reservoir pressure response to sea tide loading gives an indication of dynamic pore volume compressibility. The P wave modulus derived from sonic and density log data is shown to be very effective for the characterization. Even if a field is proved to have high pore volume compressibility, sufficient connected volume is required to benefit from the compaction drive and achieve sufficient recovery. Connected volume for the three fields included for the screening study is evaluated with aquifer mapping, comparison of pressure gradients with regional trends and consideration of potential barriers including faults and heavy oil at the oil water contact which is observed for one of the fields. The implications of these observations for field development planning are reviewed.

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