--> Eagle Ford Shale Petrophysical Characterization Using Deterministic Models Calibrated With Core Analysis From USGS Gulf Coast #1 West Woodway Research Borehole, McLennan County, Texas

AAPG ACE 2018

Datapages, Inc.Print this page

Eagle Ford Shale Petrophysical Characterization Using Deterministic Models Calibrated With Core Analysis From USGS Gulf Coast #1 West Woodway Research Borehole, McLennan County, Texas

Abstract

The U.S. Geological Survey (USGS) drilled a research borehole into outcrop of the surface equivalent of the Cenomanian-Turonian Eagle Ford Shale in McLennan County, Texas. A comprehensive geophysical logging suite and 601 ft of continuous core were obtained to advance the understanding of the stratigraphy, burial history, and depositional environment of the Eagle Ford Shale. Deterministic petrophysical modeling, specifically for pure shale reservoirs, was conducted on the comprehensive logging suite and calibrated using results from core analysis. Petrophysical models for minerology, clay volume, total organic carbon (TOC), shale porosity, pore-fluid fill, and fluid saturation were derived. Models were calibrated with Fourier Transform Infrared Spectroscopy (FTIR) results from analysis of core data. Volume of clay was determined using gamma ray and neutron-density separation. Volume of TOC was calculated using a density-TOC linear relationship calibrated with FTIR data. Multi-variable linear regression techniques were used to populate lithology models using gamma ray, bulk density, and neutron porosity curves. The contribution from sonic was found to be minimal, likely due to the lack of overburden stresses in outcrop. Carbonate content was determined using three-point volumetric techniques taking into account TOC, clay, and quartz and feldspar.

Using petrophysical models for lithology, several distinct geological zones were interpreted based on fluctuations in volumes of clay, TOC, and carbonate content. These zones correspond to the outcrop equivalent units within the Eagle Ford Shale. Deterministic porosity models for pure shale reveal higher porosities, as expected in an outcrop setting. Eagle Ford Shale is thermally immature at this shallow depth, and the pore-fluid saturation is meteoric water. The stress regime was characterized using sonic, density, porosity, and caliper data. Results indicate that principle horizontal stresses, wellbore stresses, as well as overburden compaction in this near-surface environment are negligible. No drilling-induced fractures were interpreted on the optical televiewer log, which implies that geomechanical stresses are minimal in this wellbore.