Moya Little, President
Western Divestments
Suite 105, 214 - 11 Avenue SE,
Calgary, Alberta, Canada
T2G 0X8

Phone: (403) 543-4080

> Geology

In the Giddings field the Austin Chalk consists of interbedded chalk and marl deposited in a low-energy, open-marine setting. The formation ranges from 150 to 750 ft. in thickness and displays limited matrix porosity (1–5%) and permeability (0.003–0.03 md). Hydrocarbon production from the Austin Chalk is derived from an extensive network of natural fractures. Localization of these fracture networks is controlled by bending of the formation in areas with a gentle southeast dip.

Clean chalk beds fracture when bent, whereas the more ductile marl/shale beds will not. Local disturbance by salt domes also influences fracture development.

Austin Chalk oil is sourced from the Eagle Ford shale which currently lies within the oil generation window in the Giddings field at a depth of 9500 feet. The Eagle Ford began generating oil in this area approximately 10 Ma and the top of the Eagle Ford entered the oil window approximately 4 Ma. Fracturing in the Austin Chalk began in Late Cretaceous, and the subsequent generation of oil allowed for the migration into the fractured Austin Chalk reservoir.

Early Austin Chalk explorers in the Giddings Field recognized the correlation between the interconnected chalk fracture development and significant Austin Chalk oil production. The exploitation of the fracture systems was greatly improved in the mid-eighties with the implementation of horizontal drilling. Horizontal drilling techniques allowed wellbores to contact much higher numbers of individual fractures within fracture swarms achieving much higher per well IP’s and EUR’s. Table 1 below illustrates the incremental reserve-adds and recoveries in numerous counties on the Austin Chalk trend since horizontal development was implemented including Fayette County. The chalk produces 30 API oil in the Fayette area.

Table 1 Austin Chalk Trend Horizontal Wells by County


County No. of Wells 
(After 1987)
Cumulative Oil (MMBO) Avg Ultimate
Recovery (MBO)
Avg Peak
Brazos Co., TX 245 23.02 155.05 14,249
Burleson Co.,  TX 286 24.03 187.89 8,069
Dimmit Co., TX 109 7.2 86.17 7,218
Fayette Co., TX 317 33.99 200.2 13,538
Frio Co., TX 408 27.24 82.92 6,658
Gonzales Co., TX 142 8.77 77.88 7,416
LaSalle Co., TX 124 7.69 79.56 8,633
Lee Co., TX 115 11.19 153.28 11,743
Wilson Co., TX 51 2.24 62.47 3,824
Zavala Co., TX 93 15.28 199.13 12,387