TECHNICAL PROGRESS

RESERVOIR FRAMEWORK

In all, 62 Texaco-designated reservoirs gas and oil reservoirs occur within Starfak and Tiger Shoal fields: 15 in Starfak and 47 in Tiger Shoal. In accordance with Texaco's established reservoir nomenclature, these sandstone-body reservoirs are named, in descending order, A through Z sands (some are variously subdivided using alphanumeric designations, such as T-1 sand and M-1 [lower] sand), 12000 A sand, 12000 B sand, and the Robulus L-1 through Robulus L-8 sands. Reservoir sandstones range in depth from about 6,200 to 16,200 ft in Starfak field and 6,000 to 15,400 ft in Tiger Shoal field.

Many of the Texaco-designated reservoir sandstones approximately coincide with key sequence-stratigraphic (chronostratigraphic) boundaries. Among other benefits, this coincidence greatly aided in the precise correlation of sandstone-bearing intervals across the 4 mi undrilled structural saddle between Starfak and Tiger Shoal fields. With only two exceptions, Texaco-designated reservoir sandstones are approximately correlative between the fields.

RESOURCE DISTRIBUTION

Starfak field, discovered in 1975, comprises 53 wells, most of which are gas producers. Starfak produces gas from 13 primary reservoirs and oil from 12 reservoirs. Tiger Shoal has produced gas and oil since 1958 from 103 wells. Oil wells are located primarily on the east side of the field, mainly in Block 217. Productive sandstones generally occur stratigraphically higher in Tiger Shoal wells than in Starfak wells. Tiger Shoal produces from 27 primary reservoirs.

Within individual fourth-order systems tracts, hydrocarbons have been produced from (1) sandy lowstand incised-valley fills, (2) deltaic/strandplain sandstones of late highstand systems tracts, (3) deltaic sandstones of late lowstand deltaic wedges, and (4) transgressive bayhead deltaic sandstones. However, calculation of the vertical distribution of production in Starfak and Tiger Shoal fields indicates that the vast majority of gas and oil production is from the third-order lowstand systems tracts at the bases of the third-order cycles. Within Starfak and Tiger Shoal fields (through July 1, 2000), 92.6% of total hydrocarbon production has come from the lowstand systems tracts of the third-order sequences. This observation has major implications for exploration of new hydrocarbon reserves within the area encompassed by the 3-D seismic volume. Extrapolation of key sequence-stratigraphic surfaces that bound the third-order lowstand systems tracts from the fields throughout the seismic volume is an effective means of defining the regional distribution of these proven hydrocarbon "pools."

All available reservoir (particularly petrophysical) data are being scrutinized to, for example, identify sand zones for possible work-over or to better explain the production behavior of certain intervals. Temperature, pressure, and fluid characteristics are being analyzed on a reservoir basis to be used in the determination of production evaluation, volumetrics, and reservoir modeling.