Connectivity Assessment of Heavily Compartmentalized Reservoirs: A New Workflow Introducing Areal Downhole Fluid Analysis and Data Integration

Abstract

Hydraulic connectivity assessment is vital to the development of deepwater reservoirs where inaccurate characterization often results in production under-performance. Connectivity realizations are necessary for production forecasting, completion and production planning, and successful waterflood, to name a few. Seismic surveys are not always sufficient to evaluate lateral connectivity as detected faults can be transmissive or partially transmissive. Vertical connectivity represents another uncertainty where, in many cases, pressure measurements and conventional well logs are unable to detect the presence of baffles along oil columns. In moderately complex reservoirs, basic downhole fluid analysis (DFA) workflows have proven adequate to assess reservoir connectivity. However, heavily faulted reservoirs entail a comprehensive interpretation approach to address their abnormal spatial complexity. We describe a new interpretation workflow to evaluate the hydraulic connectivity of heavily compartmentalized reservoirs which comprises three pillars: areal downhole fluid analysis (ADFA), data integration, and reservoir fluid geodynamics (RFG) analysis. The concept of areal downhole fluid analysis (ADFA) is introduced to assess local connectivity leading to global, reservoir-scale connectivity. Through data integration, we analyze laboratory pressure-volume-temperature (PVT) reports, pressure surveys, well logs, and geochemistry, to establish consistency. Each data type provides insights that are pieced together to enhance consistency and reduce uncertainty. Additionally, we examine reservoir fluid geodynamics (RFG) processes that explain the reasons behind varying oil compositions and properties in different compartments, such as oil biodegradation and water washing. Our interpretation workflow provides a robust means for classifying faults into sealing, transmissive, or partially transmissive faults, as well as for detecting sub-seismic faults. The new interpretation workflow is implemented to examine a complex deepwater oil field in the Gulf of Mexico, resulting in a reliable description of hydraulic connectivity. Faults which were previously regarded as sealing faults were classified into sealing or partially transmissive faults. Sub-seismic faults were also detected as part of the interpretation. Additionally, we observed an asphaltene clustering trend that caused high oil viscosities toward the bottom of one sandstone. A correlation formula was derived and successfully used to estimate high oil viscosities where asphaltene clustering was expected.