A Continuous Mineralogical Record of an Eagle Ford Group Core and Related Formations in South Texas Using Hyperspectral Imaging

Abstract

Hyperspectral imaging, or imaging spectroscopy, is a non-destructive analytical technique that combines digital imaging and spectroscopy. It uses a combination of short- and longwave infrared light (SWIR and LWIR) to generate mineral maps of the core surface. This technology is new to the oil and gas industry for studying cores. Generally speaking, the SWIR is a better detector for phyllosilicates whereas carbonates, quartz, and feldspars are better accounted for by LWIR. A 325 ft long, well-preserved continuous core (L1) in South Texas, La Salle County, was analyzed using hyperspectral core imaging by ALS Reservoir Laboratories. The cored interval covers the following stratigraphic units: Del Rio Formation, Buda Formation, Eagle Ford Group, and lower Austin Chalk Formation. The objectives of this study are to (1) investigate the applicability of hyperspectral imaging to reservoir characterization, (2) record and produce a continuous mineralogical record across a south Texas Upper Cretaceous core, (3) document and study the textural and fabric features, (4) define the different clay types, (5) study the observed cyclicity of the Eagle Ford in terms of mineralogy, (6) relate the hyperspectral results to total organic carbon (TOC), and (7) attempt to upscale and establish a link to wireline logs. Linking the mineralogy to reservoir properties like brittleness, TOC, porosity, and permeability will improve reservoir models. The available XRD samples span many representative samples from the various rock types which provided a reasonable degree of confidence in the accuracy of the generated single mineral abundances. Core surface mineral maps provide an insight in studying not only the mineralogical content and distribution but also the fabric and textural relationships of the highly complex, dark, and fine-grained rocks of the Eagle Ford. Identifying the different clay types and their relative distributions and abundances are critical steps to improved reservoir modeling and frac designs. Chlorite relative abundance increases in higher primary productivity intervals (radiolarian and foraminiferal dolomitic to lime packstone) and is in an inverse relationship with dolomite and quartz suggesting authigenesis of chlorite. Strontium incorporation into coccolith calcite varies by Formation and affects the resulting calcite spectral response which complicates the interpretation but may be used to infer grain-size of calcite populations.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018