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The Gum Island North field is adjacent to a small topographic feature of the same name elevated over 5 ft (1.5 m) above tidal marsh about 13 mi (21 km) west of Port Arthur, Texas. French Island field along Taylors Bayou is 4 mi (6.4 km) due north of Gum Island. The two fields, discovered as a result of the same initial exploration effort, are combination stratigraphic and structural traps. The principal reservoirs are Oligocene middle Frio-Hackberry in age. They are localized as a result of rapid filling of downward troughs created by older growth-fault structural movement, principally of Vicksburg age, but persistent during lower and middle Frio. Pre-Hackberry structural maps, Hackberry sand-distribution maps, and structural and stratigraphic maps, both prior and subsequ nt to discovery, as well as seismic and subsurface cross sections, demonstrate the nature of the oil and gas traps, as well as the geologic history of the area.
At both French Island and Gum Island, an erosional surface of significant magnitude is at the base of the Hackberry. The resulting unconformity does not greatly affect Hackberry accumulation at French Island, but at Gum Island the stratigraphic position of the unconformity relative to older beds is not only indicative of strong structural uplift, but it also bears a direct relation to individual subsequently deposited Hackberry sand reservoirs.
Exploratory drilling prior to discovery is described, along with an exploration philosophy requiring knowledge of the geologic history and depositional patterns of the trend, detailed geologic analysis of drilling results, stratigraphic integration of paleontologic data, as well as detailed and imaginative geologic use of seismic data, all with a long-term will to persist.
Statistics concerning reserves of oil and gas discovered as a result of this exploration are not made a part of this report. However, the results are expected to be 150 to 250 Bcf of gas and 6 to 10 MM bbl of oil and condensate when ultimately developed. The topside numbers could easily double when additional expected local turbidite "potholes" are drilled.
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