Moya Little, President
Suite 105, 214 - 11 Avenue SE,
Calgary, Alberta, Canada
Phone: (403) 543-4080
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
|Cumulative Oil (MMBO)||Avg Ultimate
|Brazos Co., TX||245||23.02||155.05||14,249|
|Burleson Co., T||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., T||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|