Sedimentary and Diagenetic Controls on Petroleum System Characteristics of the Upper Cretaceous Eagle Ford Group, South Texas
Abstract
Early diagenetic carbonate cements can affect brittleness and total organic
content in shale reservoirs. Predicting these effects could potentially improve recovery
efficiency and field development costs, and decrease the environmental impact of
developing the field. In this study, an X-ray fluorescence spectroscopic technique was
used to test for correlations between primary depositional features, diagenetic carbonate
cements, and organic content and fracture distributions in core samples from the Eagle
Ford Group in McMullen County, Texas. Organic content varies significantly between
diagenetic facies, with the least organic matter present in coarsely mineralized shales.
This result is consistent with the hypothesis that diagenetic carbonate cementation that
was early relative to compaction diluted primary organic matter. In contrast, total
fracture length varies significantly between depositional facies, with the lowest total
fracture length per length of core present in massive shales. Carbonate diagenesis
therefore likely did not exert a significant control on the formation of the bedding-parallel
fractures observed in this study; instead, laminated fabrics provided planes of
weakness along which stress release fractures or hydrocarbon generation-induced
fractures could develop. The suggested target reservoir facies for similar Eagle Ford
wells is a finely to moderately mineralized laminated shale because of the likelihood of
finding high organic content and horizontal fractures that would increase the effective
rock volume in communication with primary hydraulically induced fractures.
Citation
Hancock, Travis A (2014). Sedimentary and Diagenetic Controls on Petroleum System Characteristics of the Upper Cretaceous Eagle Ford Group, South Texas. Master's thesis, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /152863.