Abstract

Geraldine Ford field produces from the upper Bell Canyon Ramsey sandstone in Reeves and Culberson Counties, Texas. Production from this and other upper Bell Canyon fields in the Delaware Basin occurs from the distal (southwest) ends of northeast-oriented linear trends of thick Ramsey sandstone deposits. The Ramsey sandstone is composed of a 0- to 60-ft-thick sandstone bounded by laminated siltstones. In the northern part of the field the reservoir is divided into two sandstones (Ramsey 1 and 2) separated by a 1- to 3-ft-thick laminated siltstone. In the southern part of Geraldine Ford field, only the Ramsey 1 sandstone is present. The underlying Ford and overlying Trap siltstones are composed of organic-rich siltstone laminae inter-bedded on a millimeter scale with organic-poor siltstone laminae. The Ford and Trap siltstones display gradational contacts with fissile, highly organic siltstones interpreted as basinal condensed sections.

On the basis of core descriptions, log correlations, and study of an outcrop analog, Ramsey sandstones are interpreted as having been deposited by sandy, high- and low-density turbidity currents. The sands were deposited in a basin-floor setting in a channel-levee system with attached lobes. Channel facies are approximately 1,200 ft wide and 15 to 35 ft deep. They consist of massive and crossbedded sandstones interpreted to have been deposited from high-density turbidity currents. Channel margins, characterized by rippled and convoluted sandstones interbedded with minor siltstones, are interpreted as channel levees formed by overbanking of low-density turbidity currents. Lobe sandstones are interpreted as being deposited at the mouth of the channel by high-density turbidity currents. They were identified by massive and graded sandstones with load and dewatering structures that include flame structures, dish structures, and vertical pipes.

Laminated Ford siltstones coarsen upward, and the organic-poor laminae increase in thickness toward the Ramsey sandstone. The overlying Trap siltstones fine upward away from the sandstone as the organic-poor laminae decrease in thickness. This pattern suggests that the laminated siltstones are part of the progradation and retrogradation of the channel-levee and lobe system; the siltstones may represent the most distal part of the lobe. Alternatively, the siltstones may represent windblown silt from the shelf margins. Periods of relative sea-level fall may have exposed increasingly larger areas on the shelf and allowed the wind to carry away greater volumes of silt, resulting in thicker organic-poor siltstone layers.