Abstract

Domestic exploration within established petroleum provinces has become a major challenge to all involved in the search for hydrocarbons. Explorationists must concentrate on identifying subtle traps to define high-quality prospects with enticing reserves. Critical decisions involve where and how to explore for these. Factors such as play attractiveness, complexity of exploration, proper risking, and rigorous economic analyses are key to our success and selection of work areas.

Play/prospect attractiveness (PA) is a function of factors such as total reserves, production rates, probability of success, payout time, total costs, and exploration/development difficulty. (PA) is directly proportional to the first three factors and inversely proportional to the last three. The influence of these factors on (PA) must be assessed and internal standards set. (PA) may be expressed as a dimensionless number to be used for ranking criteria. Prospect risk must be accurately determined. Trap/seal, reservoir, source, recovery, and timing may be displayed numerically using a predetermined scale. Success probability is a function of their product. Rigorous economic analyses are needed to insure that time, money and effort are well spent. Many methods are used, being a matter of philosophy and preference. The investment efficiency index described by Megill, and the growth rate of return of Capen et. al. are considered the most satisfactory, followed by the traditional internal rate of return.

Two geological play type have been selected for discussion. The Mississippian (Miss) play of Gove County, Kansas involves structural closures of about 4.5 meters and 2 to 3-well fields with average recoveries of 45 MBO/well at depths of 1,364 meters. Prospects are identified through a series of maps such as (Miss) structure, Lansing to (Miss) isopach, net-limestone isopach of the upper 6 meters of (Miss) strata with specific porosity and resistivity cutoffs, and pressure-gradient maps. The Caddo limestone/conglomerate play of Montague County, Texas, consists of structural/stratigraphic prospects with structural closures of about 7.5 meters and 3 to 5-well fields with average recoveries of 60 to 100 MBO/well at depths of 1,970 meters. Leads may be identified using gravity data and regional seismic. Well control is tied to the seismic using synthetics from sporadic sonic logs and from resistivity logs using the Faust equation. Detailed seismic and seismic stratigraphy are key for prospect definition.