American Oil and Gas Reporter - March 2016 - 63

SpecialReport: Unconventional Resource Science

FIGURE 1
Brazos Basin Regional Map
Faults/Folds
Salt Diapirs
Lakes
Buda Structure
Brazos Basin

Austin Chalk

100'
200'

300'

Woodbine

400'
500'

Buda

Lower Eagle Ford

600'

Georgetown

Regional Framework
While intimately linked to the East
Texas Basin, the Brazos Basin is separated
by the Angelina Caldwell Flexure (Figure
1) through the Mesozoic and Lower Cretaceous. The structural setting accommodated the deposition of a series of
Cretaceous source rocks (i.e., Bexar and
Lower Eagle Ford) and a thick Lower
Cretaceous carbonate platform from the
Edwards Reef northwest to the Bossier
Shelf (Figure 2). In the depocenter of the
basin in Brazos, Grimes and Madison
counties, stratigraphic thicknesses can
reach 30,000 feet.
The basin has at least three significant
source rocks:
* The Jurassic Smackover is well
through the gas window and primarily
sources deep gas reservoirs such as the
Cotton Valley and Bossier. Located near
the base of the Brazos Basin, the Smackover is deeper than 17,000 feet.
* A variety of Lower Cretaceous
shales sit in the oil window in the updip
portion of the basin and through the
active gas window in the downdip portion.
With varying thicknesses and few well
penetrations, the contribution and spatial
distribution of hydrocarbons within the
Lower Cretaceous is not well understood.
* The Lower Eagle Ford was deposited
throughout the basin with varying amounts
of terrigenous input. At its most distal

FIGURE 2
Stratigraphic Column of
Cretaceous Section of Interest

Upper Cretaceous

and the cost environment.

Lower Cretaceous

Parts of Brazos, Burleson, Leon, Madison and Robertson counties along the
western flank of the basin combine good
source rock facies with conventional
reservoirs, creating a prolific stacked interval with multiple horizontal targets.
Horizontal drilling and hydraulic fracturing
have opened the Lower Eagle Ford and
accelerated production in tight reservoir
facies of the various intervals. Anadarko
Petroleum, Apache, CH4 Energy, Clayton
Williams, EOG Resources, Halcón Resources and Hawkwood Energy have led
the charge to prove the Lower Eagle
Ford's economic viability, and it continues
to provide compelling results.
Hawkwood was formed in 2011 and
commenced operations in August 2012
with a primary focus on developing unconventional liquids opportunities in East
Texas, as well as additional exploration
projects in the Rocky Mountains. Through
acquisitions and leasing, Hawkwood now
controls more than 75,000 acres in an
area within the Brazos Basin that contains
at least six reservoir targets and can exceed
50 million barrels of oil per section.
Through a process of maximizing and
enhancing the value of the area, Hawkwood's multidisciplinary team has collected
a series of whole and sidewall cores, and
has horizontally tested four landing zones.
With a variety of play concepts being
pursued in the basin, there is an assortment
of viable targets with a range of economic
profiles, depending on commodity prices

700'
800'
900'
1,000'
1,100'
1,200'
1,300'

and thin deposition in Lee and Burleson
counties, it is beneath the South Texas
Upper Eagle Ford. The Lower Eagle Ford
has sourced the underlying Buda and
Georgetown, Woodbine sands, and Austin
Chalk. It is actively generating oil and
exhibits a narrow band of volatile oil at a
depth of approximately 9,000 feet.
Austin Chalk
The Austin Chalk is at the top of the
interval of interest. Composed of a series
of marls, shale and biomicrite, the chalk
has three to four members that frequently
are separated by bentonites. The gross
interval thickness ranges from 150 to
700 feet, with the fractured upper and
lower members contributing the majority
of the pay. Occasionally, the lower member
develops an organic-rich facies, which
can complement the underlying Eagle
MARCH 2016 63

American Oil and Gas Reporter - March 2016

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