Occurrence of Oil in the Austin Chalk at Van Field, Van Zandt County, Texas: A Unique Geologic Setting: ABSTRACT

Abstract

ABSTRACT Important new shallow Austin Chalk production has been established above the principle Woodbine production at Van Field in the East Texas Basin. The geologic setting and reservoir characteristics of the Austin Chalk at Van Field are unique. Shallow burial allowed the Austin Chalk to retain its primary microporosity, unlike the typical deep fractured chalk reservoirs in Central and South Texas. The Van Field structure is a complexly faulted anticline and is approximately 1,500 ft (457 m) higher than surrounding structures. Whole core analyses show that the Van Field Austin Chalk is a very fine-grained limestone composed primarily of coccoliths. Although porosity ranges from 15-35%, permeability is very low with values ranging from 0.01-01.5 md. No evidence of significant natural fractures or microfractures were observed in the cores. Occurrence of oil in the Austin Chalk has been known since the field discovery in 1929. Increased production rates of up to 250 BOPD have been possible with the recent development of a large fracture stimulation technique. Reservoir limits of the Austin Chalk were determined by isopaching resistivity and porosity. A direct correlation appears to exist between Austin Chalk productivity and the structural position and detrital clay content of the chalk. Development of the Austin Chalk reservoir at Van Field continues and has already added significant reserves to the field.