Toward an Accurate Reservoir Model of Heterolithic, Tidally-Influenced Deposits: An Ongoing Case Study in the Sego Sandstone Member of the Mancos Shale Through Second-Generation, Outcrop-To-Subsurface 3-D Modeling

Abstract

Heterolithic tidal reservoir units are prolific in hydrocarbon settings around the world, but are often overlooked or underestimated as a contributor to total volume, due to their complex lithologic and architectural nature. A first generation DecisionSpace model investigating these deposit types used detailed outcrop correlations from the Sego Sandstone of Utah and Colorado, of six key bounding surfaces within an ~60–100 m thick interval. The model was ground-truthed by 39 outcrops, core-scale descriptions of facies, bed thicknesses, bioturbation indices, gamma responses, permeability and porosity measures, and net sand percentages. These points and correlation panels were tied to 36 wells in the adjacent subsurface to form the initial framework for modeling. Early injector and producer runs of this first-generation model showed a need to collect additional information for the second-generation Petrel model, on lithotypes with specific attention to tidal channels, swatchway incisions, architectural differences between unconfined and confined tidal bars, and the influence of bioturbation layers. In addition, ongoing work in the nature of shale architecture (Burton and Wood, 2013) has been integrated into the second-generation model and its impact will be discussed. Finally, we analyze the gridding algorithms between software packages to more accurately characterize subsurface geometries and ensure best prediction of lithofacies distributions using this incredibly detailed and well controlled tidal reservoirs data set. Results show the importance of understanding the sub-seismic scale nature of tidal bar-intrabar architectural element couplets, as flow, seeking high permeability pathways, will strand resources in elements. Outcomes also demonstrate the importance of understanding the extent and nature of incisional features for creating connectivity between layers.

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