Studies—Carbonate Distal Slope and Basin Floor Development
2014. "Studies—Carbonate Distal Slope and Basin Floor Development", Deposits, Architecture, and Controls of Carbonate Margin, Slope and Basinal Settings, Klaas Verwer, Ted E. Playton, Paul M. (Mitch) Harris
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Outcrop-based, reservoir-analog models are important tools for assessing reservoir potential and efficient schemes for exploitation in the subsurface. A new outcrop reservoir-analog model is documented herein for Upper Miocene deep-water sediment-gravity-flow and hemipelagic deposits within the Agua Amarga basin, southeast Spain. This study demonstrates that large volumes of resedimented deposits exhibiting high ratios of potential reservoir to baffle facies (net to gross) accumulate where funneling topographic features focus sediment-gravity flows from the long linear dimension of a carbonate platform into a confined channel (focused flow). Where topographic funneling features are absent, and where a short linear dimension of the carbonate platform margin is available as a source of sediment-gravity flows, deposits accumulate with lower volumes and high proportions of baffle facies (dispersed flow).
Extensive outcrops in the Agua Amarga basin allow for characterization of facies and facies architecture using measured sections, photomosaics, and core-plug petrophysical data. Petra™ and Petrel™ were used for correlation, data integration, and static geomodeling to create a reservoir-analog model that synthesized geological observations noted in outcrop. Facies modeled as reservoir units consist of graded fine-to very coarse-grained skeletal packstones and fine-to very coarse-grained breccias. Graded skeletal packstone facies exhibit a mean porosity and corresponding permeability of 30.5% and 136 mD; breccia facies exhibit a mean porosity and corresponding permeability of 30% and 65 mD. Facies modeled as baffle units consist of foraminiferal, volcaniclastic foraminiferal, and skeletal foraminiferal wacke-packstones. These planktonic foraminifera-rich facies exhibit a mean porosity and corresponding permeability of 36% and 12 mD.
Paleotopography, in conjunction with sea-level history, largely controls the geometry, lateral continuity, and volume of a given reservoir body. Paleotopographic differences that lead to focused flow versus dispersed flow result in markedly different reservoir properties. Static model volumetric results reveal that compared to the dispersed-flow system, deposits within the focused-flow system have greater reservoir to baffle facies volume ratios (0.70 compared to 0.09), and greater reservoir facies bulk volumes (46.5 million m3 compared to 18.6 million m3). Further, the ratio of reservoir facies bulk volume to linear dimension of the shelf margin supplying both the focused-flow and dispersed-flow systems is similar, suggesting that deep-water reservoir volume may be predictable on the basis of the linear dimension of the shelf margin. Finally, interrogating modeled reservoir facies for different connected volume scenarios offers significant insight relevant to subsurface exploitation strategy and supports observations noted in the field.