Bioturbation changing porosity, permeability, and fracturability in chalk? Insights from an Upper Cretaceous chalk reservoir (Buda Formation, Texas, USA)

Abstract

The continuous rise in hydrocarbon demand, the production decline in conventional oilfields, and the remarkable improvement in extraction methods have allowed the hydrocarbon industry and subsequently, geoscientists, to turn to studies on both unconventional and mature fields with untapped potential. In such reservoirs, the application of advanced drilling, completion, and production techniques must be preceded by the identification of permeable stratigraphic intervals that favour commercial exploitation. Accordingly, bioturbated deposits can play a key role in providing permeable pathways for enhanced production. Herein, we analyse the effects of bioturbation on the porosity and permeability of the Buda Formation, a highly bioturbated, tight (low-porosity matrix) Upper Cretaceous chalk reservoir from the Texas Gulf Coast Basin, which has been commercially exploited because of the occurrence of natural fractures. Our results show that (in addition to the natural fractures) burrows (and borings) substantially increased the porosity and permeability of this formation, thus, potentially contributing to enhanced hydrocarbon (or groundwater) storage and production. These biogenic structures might also have favoured the development of natural fractures and stylolites in the Buda Formation. However, further studies are required to prove this hypothesis.

Keywords:

• Buda Limestone
• porosity
• permeability
• micro-CT
• fracability
• Rock Reservoir

Acknowledgments

We thank Blaine Novakovski and Micheal St. Pierre for the preparation of the rock-thin sections. The final version of this manuscript benefited from detailed and valuable comments made by Greg Baniak, Abdullah Alqubalee, Hillary Corlett, and Murray Gingras.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was financially supported by the University of Saskatchewan, the American Association of Petroleum Geologists, the Canadian Society of Petroleum Geologists and Cenovus Energy (scholarships awarded to F.L. Valencia), as well as by funding from the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants 311727-20 and 422931-20 awarded to Mángano and Buatois, respectively. Mángano also thanks funding from the George J. McLeod Enhancement Chair in Geology.