Regional Assessment of the Eagle Ford Shale: Insights From Lithology, Water Saturation, Organic Richness and Productivity Correlations

Abstract

Many studies have described the lithologic and facies variations in selected areas of the Eagle Ford Shale but a comprehensive regional investigation linking productivity to facies, lithology, organic matter and water saturation variations has not been presented to date. The Upper Cretaceous Eagle Ford Shale in South Texas is an organic-rich, calcareous mudrock deposited during a second-order transgression of global sea level on a carbonate-dominated shelf updip from the Sligo and Edwards reef margins. Lithology and organic-matter deposition was controlled by fluvial input from the Woodbine Delta in the northeast, upwelling along the Cretaceous shelf edge, and volcanic and clastic input from distant Ouachita and Laramide events in the southwest. Global organic anoxic event (OAE2) contributed to preservation of this organic-rich source rock. These paleogeographic and tectonic elements controlled variations of lithology, amount and distribution of organic matter, and facies that have a profound impact on production quality and production forecasts. A database of wireline logs, total organic content (TOC) calculated from wire line logs (delta log R method), water saturation, lithology, porosity, and thickness of the Lower Eagle Ford was created. Components of the database were used as variables in krieging and multivariate statistical analyses evaluating the impact of these variables on production. For example, TOC and water saturation show an inverse relationship whereas TOC and porosity correlate positively. High productivity zones correlate positively to higher porosity and TOC areas. This method of evaluation not only serves as a tool to predict geologic drivers of production and productivity across the field but also takes the geologic heterogeneity across the Eagle Ford play into account.

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