Sedimentology and Geomorphology of Carbonate Shoreface Systems: Implications for Geologic Modeling and Flow Simulation

Abstract

Subsurface reservoir models commonly are based on predictions derived from conceptual models and analog data regarding geobody attributes. The purpose of this project is to provide foundational input into these reservoir models and to test the hypotheses that 1) geomorphic form (e.g. size, shape, and orientation) of carbonate shoreface systems is related to internal sedimentology (e.g. grain size, sorting, and type, sedimentary structures) and 2) that depositional variability affects production from subsurface analog reservoirs. Observations from Pleistocene elongate, margin-parallel ridges on the western margin of Crooked-Acklins Platform, Bahamas, are used to develop conceptual models for carbonate shoreface systems. These conceptual models provide inputs to construct geological and numerical reservoir models, explicitly testing geologic architecture influences on reservoir performance. Along the western margin of Crooked-Acklins Platform, southeastern Bahamas elongate, margin parallel ridges terminate at exposed cliff outcrops. Continuous for up to 4.5 km, these ridges are visible on satellite imagery. Twenty measured sections along these exposures reveal vertical and lateral variability (e.g. grain size, type and sorting, sedimentary structures, and depositional facies geometries) within and among ridges. The ridges include a shallowing-upward succession dominated by trough-cross laminations and fenestral, low-angle planar laminations, representing the upper shoreface and foreshore, respectively. Grain constituent include peloids, ooids, and skeletal fragments, with dominant type varying with location. Most sections are capped by an undulatory unit of varying thickness (up to 1 m) that includes rhizoliths, laminated crusts, and karst features representing a subaerial exposure surface. Locally these deposits are associated with underlying coral framestone to rudstone. Observations of sedimentology and geomorphology of, ridges provide input for conceptual and geologic models of carbonate shoreface systems. These geologic models are used as input for flow simulations evaluating the impact of geobody architecture on flow character and exploring the impact on vertical and horizontal completion strategies. Results of this project provide predictive models for the geologic framework and production trend in analogous carbonate shoreface reservoirs.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015