Austin Chalk Fractured Play Characterization Using Well and Seismic Data in Wilson County

Abstract

The Upper Cretaceous Austin Chalk is a hydrocarbon-bearing formation that consists of interbedded chalks and marls in South Texas. Broadly, three mechanical stratigraphic units are recognized—the upper and lower fractured massive chalks separated by a middle ductile marl member (Corbett et al. 1987). The rock matrix of the whole Austin Chalk unit generally has low porosity and permeability with values of 10% and 0.5 mD or less, respectively. Porosity and permeability increase in proximity to structures (Condon and Dyman 2006), and the play is believed by many authors to be fracture-driven (Roy et al. 1981; Haymond 1991; Stowell 2001; Condon and Dyman 2006). The Austin Chalk has been a known producer since the 1920s (Parshall 2017), and there has been renewed exploration activity recently because of its liquid hydrocarbon richness.

This work explores the reservoir potential in various zones of the Austin Chalk. The study area is located in Wilson County, where wireline log, production, and seismic data are available across the Austin Chalk section. Petrophysical properties and a fracture likelihood curve were derived from basic triple combo wireline log data for each of the wells analyzed. Structural elements, such as faults and volcanic mounds, are present in the area and interpreted on seismic. Special attention is given to the proximity of these features to wells when analyzing production data, as faults/volcanics can either enhance or inhibit production. The fault likelihood seismic attribute was used to aid in fault interpretation and compared to production and fracture interpretation from logs.

Overall, two properties are considered for selecting targets in Austin Chalk wells—proximity to structures (fault or volcanic mounds) and the likelihood of a rock to propagate a fracture. The fault likelihood seismic attribute along with a fracture indicator curve derived from triple combo logs can help characterize the play and determine the best lateral landing zones. This study focuses on identifying better drilling targets in the Austin Chalk, but the presented workflow can be applied to any fractured carbonate reservoir.

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