Gas production from several, 6 to 23 ft. (2 to 7 m), single to multistory sandstone bodies of the Woodbine-Eagle Ford interval, 160 to 200 ft. (49 to 61 m) thick at 9,000 to 9,600 ft. (2,743 to 2,926 m) in the Damascas field has been developed since discovery in 1976. Subsequent offset drilling resulted in a few gas wells and several dry holes. In February 1979 the entire Woodbine-Eagle Ford interval was cored in the No. 7A Dorrance well. Sedimentologic core study generated a predictive depositional model which has guided field development of the subtle stratigraphic traps at a 5 to i well success ratio. Present gas reserves are 40 Bcf with 440,000 bbl of condensate.
The productive area is located slightly southwest of the Sabine uplift and just uxJip from the Lower Cretaceous continental shelf edge. Seismic sections and foraminiferal paleoecology establish a middle-shelf depositional setting. Bioturbated, silty, shelf shales comprise the upper and lcier Woodbine-Eagle Ford interval. The middle is a complex of, (1) graded, medium to very fine-grained, massive to laminated sandstone beds; (2) contorted, softsediment-deformed intervals; (3) swirled and sheared siltstone beds; and, (4) thin diamict conglomerate beds. Genetic units indicate periodic rapid deposition by debris flows and low to high-concentration density currents. The several distinct productive sandstone bodies (porosities 9 to 14%; pemeabilities 2 to 10 md) are northward-thickening, dip-oriented lobes.
The localized deposition in the shelf setting was controlled by delta development slightly to the north. Periodic major storms generated delta flooding which
Figures & Tables
Shelf sandstone reservoirs are becoming a more and more common exploration target. What they are, how they may be characterized, and how they differ from shoreline and deep-water deposits in the subject of this publication. Shelf sands and sandstone reservoirs are among the more poorly understood types of sandstones. Continental, shoreline and deep water sandstones have all been studied in much more depth than have shelf sands and sandstones. However, during the last fifteen years significant progress has been made in understanding shelf sands and sandstones. Studies of modern sediments have allowed us to understand many of the depositional processes active on the shelf. This book is intended to be an up-to-date summary of shelf processes and products. The papers are intended for those new to shelf sands and sandstones as well as the shelf specialist.