Reservoir-Fluid Geodynamics Enable Insights Into Reservoir Connectivity

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 23723, “Abnormal Viscosity and Other Implications of Reservoir Connectivity Inferred From Reservoir Fluid Geodynamics: A Case Study From Deepwater Gulf of Mexico,” by Tarek S. Mohamed, SPE, and Carlos Torres-Verdin, SPE, The University of Texas at Austin, and Oliver C. Mullins, SPE, SLB. The paper has not been peer reviewed. Copyright 2024 International Petroleum Technology Conference. _ Reservoirs often are compartmentalized by barriers, including structural flow barriers resulting from geodynamic processes such as faulting or depositional stratigraphic barriers such as shale breaks. Along with structural geodynamics, reservoir-fluid-geodynamics (RFG) processes such as fluid mixing define fluid systems that respond to their evolving reservoir container. The authors study RFG processes that explain the reasons behind varying oil compositions and properties within and across different reservoir compartments. The complete paper also explores how to infer fluid implications with wireline logging measurements. Introduction As reservoir structures change as a result of geodynamic processes such as faulting and fracturing, fault-block migration, anticline formation and growth, halokinesis effects, and diagenesis, reservoir fluids undergo a wide array of RFG processes that are directly affected by changing reservoir structures. Furthermore, reservoir conditions such as pressure and temperature often are different across reservoir compartments, representing another factor affecting fluid evolutions. Thus, it is critical to assess the implications of different connectivity profiles on various fluid properties such as oil viscosity and dissolved gas amount. Likewise, the evident effect of connectivity structures on fluid properties has enabled the introduction of sophisticated methodologies to use measured fluid properties to assess hydraulic connectivity, such as the use of measured oil asphaltene gradients with downhole fluid analysis (DFA) workflows to assess fluid thermodynamic equilibration as a proxy of hydraulic connectivity. Field Background In this study, fluid-chemical and geochemical data are used with seismic and geological data to examine various fluid properties as a result of different hydraulic connectivity realizations of a deepwater reservoir in the Gulf of Mexico. Additionally, simultaneous analyses of rock and fluid data allow for relating geological to fluid complexities, leading to multiple applications such as the detection of fault-block migrations of three different fault blocks across the field, enabling reliable quantification of fault throws, assessment of the sequence of faulting and fluid-charging events, and evaluation of fault sealing. The authors write that they prove that fluid compositional gradients accurately reflect current reservoir architecture and assist reservoir reconstruction.