The Lisburne is a widespread group of predominantly shallow marine carbonate rocks, largely Mississippian and Pennsylvanian in age, underlying much of Alaska's North Slope. Near Prudhoe Bay, it is divided into two formations, with the Wahoo overlying the Alapah.

Oil was discovered in the Lisburne with the drilling of the Prudhoe Bay State 1 well in 1968. An active delineation program during 1983-84 and detailed geological/geophysical studies have demonstrated the viability of the Lisburne reservoir.

Log interpretation for lithology is difficult in the Lisburne, and good core control is essential. A computerized data base has been established containing foot-by-foot descriptions for more than 5,000 ft of core. We have developed a lithofacies classification based on sediment texture, grain size and type, and dolomite content.

The upper portion of the Wahoo has received the most attention and is best understood at this time. The most distinctive features of logs in the Lisburne interval are the so-called shale marker beds. These are readily correlatable across the reservoir area and have been used as time lines to divide the Wahoo into a set of detailed subzones. The major marker beds represent distinct breaks in sedimentation. Between these breaks, lithology varies both laterally and vertically. Detailed subzones have allowed us to map individual "slices" of the reservoir and to have confidence in overall reservoir continuity. Whereas matrix porosity appears to contain most of the hydrocarbons, fracture porosity is important for the interconnection of porous intervals and for productivity of the reservoir. /P>

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