Three-Dimensional Modeling of a Quarried Deltaic Reservoir System: Atoka Formation, Arkansas

Abstract

Deltaic deposits produce billions of barrels of hydrocarbon worldwide. However, complexities and variations in deltaic geobody geometry, sediment volume, and internal architecture often result in a large amount of unproduced resource. This study focused on creating a detailed 3D reservoir model of one such deltaic system, the Pennsylvanian Atoka Formation, aided by beautiful quarry exposures. The target quarry, the Webco Quarry (WQ) located in White County, Arkansas, encompasses an area of approximately 140,000 m², with walls ranging from 25 to 45 meters high. These sediments were deposited as a series of Pennsylvanian-age deltas fed from the ancestral Appalachian Mountains, prograding westward and southward into the older Ouachita trough. The elongate nature of the trough and long distance of sediment transport resulted in this siliciclastic deltaic systems being influenced by marine processes, which included both tides and waves. To model these reservoirs, measured sections are collected and details are placed within a hierarchal framework of surfaces interpreted from Gigapan and LiDAR imagery of the quarry walls. Facies differentiation is based upon grain size, bed thickness, composition, texture, sedimentary structures, and fossil content of the rocks. Facies are predominantly fine- to medium-grained sandstones, with some intervals containing lithic clasts, granules, and pebbles. Sedimentary structures include planar laminations, ripples, and cross stratification. Some portions are fossiliferous with bioclasts and trace fossils. Shales vary in thickness and continuity, but can be placed in a hierarchy within the model. Shale lengths, thicknesses, and frequencies are collected to calculate vertical and horizontal permeability ratios for populating grids between the walls. Data has been integrated in Petrel, employing user-created training images and multiple-point geostatistical simulation. The model illustrates fluid flow connectivity of this compositional and geometrically complex reservoir, and details the importance of shale continuity and distribution in baffling and blocking flows.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016