INFLUENCE OF REACTIVATED BASEMENT FAULTS ON THE
POROSITY EVOLUTION OF SOUTH TEXAS CRETACEOUS
CARBONATES – IMPLICATIONS FOR AUSTIN CHALK PLAY
DEVELOPMENT IN TEXAS AND LOUISIANA
JEFFREY J. DRAVIS

Dravis Geological Services
Houston, Texas

Highly constrained, core-based studies of numerous Devonian pools in
western Canada document the role of reactivated basement faults in not
only entrapping hydrocarbons, but in creating their effective secondary
porosities. Whenever these faults reactivated upwards into overlying
carbonate sequences, comparable styles of burial diagenesis and
secondary porosity resulted. Diagenetic fluids from these faults moved
outward at distances ranging from 2000 feet to over two miles.
Rock-based case studies from both Glen Rose and Edwards carbonate
pools in south Texas confirmed that their reservoir quality evolved by
deep-burial dissolution of micritic facies, including some depositional
chalks, in close proximity to reactivated basement faults. Hotter, acidic
burial fluids dissolved these calcitic fabrics after the onset of pressure
solution.
Several Austin Chalk wells in Karnes County, Texas, produce at very
high rates from higher than normal matrix porosities. This production
is strikingly anomalous for the Austin Chalk trend in Texas. In light of
the deep-seated faulting in the Karnes Trough and burial dissolution in
underlying Edwards-aged carbonates, deep-burial dissolution of
depositional chalk along reactivated basement faults best explains these
Austin Chalk reservoir anomalies. Areas of current Austin Chalk activity
in south-central Louisiana are closely associated with major wrench
faults, so these aspects of Karnes Tough diagenesis and porosity
evolution should be factored into any regional evaluation of that area.

BIOGRAPHY OF JEFF DRAVIS

Jeff Dravis is a carbonate geologist whose consulting activities primarily focus on aiding
in the discovery of oil and gas deposits, or enhancing their development once they are
found. He also conducts numerous applied carbonate training seminars for industry every year.
Jeff received his Bachelor of Science degree in Geology from St. Mary’s University in
San Antonio, Texas. He received a Master of Science degree in Marine
Geology from the University of Miami’s Rosenstiel School of Marine and
Atmospheric Sciences. His thesis was entitled “Holocene Sedimentary Environments on
Eleuthera Bank, Bahamas.” Jeff then entered Rice University, Houston, Texas, to
work on deep-water carbonates under the direction of Dr. James Lee Wilson.
He was awarded a Ph D in Geology; his dissertation was entitled “Sedimentology and
Diagenesis of the Upper Cretaceous Austin Chalk Formation, South Texas and Northern
Mexico.”
Dr. Dravis began his professional career with Exxon Production Research
Company in Houston. There, he conducted applied research on carbonate facies,
diagenesis and porosity evolution, but also headed up Exxon’s worldwide training
efforts in carbonates. This training included teaching in-house seminars, as well as leading
combined modern (Bahamas and Florida) and ancient (Texas and New Mexico)
carbonate field seminars for the corporation.
In 1986, Jeff started his own consulting practice in Houston. First, he founded
Dravis Interests, Inc. to provide technical expertise and training in applied carbonate petroleum
geology for the oil and gas industry. Then Dravis Geological Services was created to handle
all technical consulting projects. Jeff has been involved in over 180 technical projects
worldwide, working sequences ranging in age from Cambrian to upper Tertiary. He has
presented over 275 in-house and field seminars to industry, both on a public and private basis,
including dozens of seminars to Caicos Platform in the southeastern Bahamas. Over the past
year, this training includes presenting over 18 private versions of a one-day seminar entitled:
“Overview of the Austin Chalk in South Texas and Louisiana: Depositional Setting,
Diagenesis, Porosity Evolution and Play Development.” His clients are domestic and foreign
oil companies, both majors and independents.
Jeff is an adjunct Professor of Geology at Rice University in Houston, where he teaches parts
of courses, takes students into the field, and periodically serves on theses committees. He has
published over 25 papers and given nearly 45 talks at local and national geological meetings.
For the past two years, he has taught the carbonate geology segment of the University of
Houston’s Professional Master’s Program in Petroleum Geology.
Jeff Dravis website: http://www.dravisinterests.com