A Laterally Accreting Grainstone Margin from the Albian of Northern Mexico: Outcrop Model for Cretaceous Carbonate Reservoirs
David A. Osleger, Roger Barnaby, Charles Kerans, 2004. "A Laterally Accreting Grainstone Margin from the Albian of Northern Mexico: Outcrop Model for Cretaceous Carbonate Reservoirs", Integration of Outcrop and Modern Analogs in Reservoir Modeling, G. Michael Grammer, Paul M. “Mitch” Harris, Gregor P. Eberli
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Exceptional exposures of progradational platform margin slopes of Albian age were mapped along a 5-km, near-continuous, dip-oriented transect in northern Mexico with the goal of producing an outcrop model for analogous Cretaceous reservoirs. The study area at the El Cedral is located along the western margin of the Devils River grainstone belt flanking the muddy, intrashelf Maverick Basin. Four relatively complete clinothems and portions of two adjacent clinothems are recognized in the Las Pilas Formation in the study area. The Las Pilas clinothems exhibit complex sigmoid-oblique geometries and have dimensions of 40–60 m of vertical relief, depositional dip angles of foreset beds ranging from 8 to 15°, and dip-oriented lengths of 1–2 km. Internally, in foresets of clinothems, thick- to massively bedded, sigmoid- to oblique-shaped lenses exhibit overlapping, seaward-stepping patterns toward the southeast.
The primary sediment fabrics of topset, foreset, and bottomset beds of the Las Pilas clinothems are grainstones and grain-rich packstones. Coated grains are the predominant grain type, with subordinate amounts of micritized mollusk fragments and intraclasts. Porosity is predominantly moldic, but primary interparticle porosity is common. These lime sands were winnowed, coated, and micritized along the high-energy topsets of clinoforms before being exported seaward toward the breakpoint, where they cascaded onto the steep frontal slopes as sporadic grain flows or mass flows. The master bounding surfaces that define the clinothems likely represent episodes of nondeposition and abandonment of the surface, perhaps occurring during shifts in the locus of deposition laterally along the shoal margin.
The architecture and composition of the Las Pilas clinoforms provide observable data for comparison with analogous subsurface reservoirs in the Aptian Shuaiba Formation (Bu Hasa field) and Cenomanian Mishrif Formation (e.g., Umm Adalkh field) of the Arabian Gulf.
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Building robust 3-D reservoir models is a major challenge that requires incorporation of geologically defined input parameters. This publication provides an overview of current approaches used in the development of geologically constrained and integrated reservoir models. Each of the 18 papers addresses various stages in the process of creating a reservoir model through the development and incorporation of an analog, extracting the quantitative input parameters on lateral and vertical variability, and the development and modification of a 3-D reservoir model based upon geologically constrained data. This applied volume is divided into two sections. The first is a set of papers illustrating the value and methodology of acquiring geometrical data on the lateral and vertical distribution of reservoir facies, within a sequence stratigraphic framework, using both outcrop analogs and detailed study of modern depositional systems. The second section includes both case studies where outcrop and modern analog data have been incorporated into subsurface reservoir models, as well as papers that illustrate recent advances in simulation and geostatistical methodologies. Together, the two sections provide a comprehensive look at integrated reservoir modeling.