Abstract

The majority of E&P companies that have acreage positions in “sweet spots” of the WolfBone Unconventional Resource play were and/or are continuing to target conventional sandstone reservoirs in Third Bone Spring and middle to lower Wolfcamp sandstones. These traditional reservoirs are above and below, respectfully, a 1,000’ thick quartz, carbonate, kerogen and oil-rich Wolfcamp Shale interval. The Wolfcamp Shale has magnitudes more oil in place and is proving to be a more successful economic objective than vertical and horizontal wells being drilled in the traditional sandstone reservoirs. Additional intervals in the Second and First (Avalon) Bone Spring section together with these intervals provides more than 3,000 foot thick vertical section currently being developed in the southern Delaware Basin.

The Wolfcamp Shale is an ideal heterogeneous resource consisting of quartz, carbonate and kerogen. Exploration and field development will be successful over a large area. However, the geologic and economic “sweet spot” is limited to the proximal basin floor on the gently-dipping western flank of the southern Delaware Basin. In this setting, quartz and kerogen accumulated in the quiet deep-basin interrupted by episodic deposition of shelf to basin floor carbonate debris flows and slope to basin floor quartz-rich debris flows that settled just basin ward of the deceleration boundary between the slope and basin floor. These depositional processes resulted in compositional and grain-size heterogeneities and accumulation of thick organic-rich, technically and economically exploitable targets.

During maturation large volumes of oil were sealed in place (108 MMBOIP per Section). Expansion from kerogen to oil in a sealed system resulted in overpressure that created numerous, still-open fractures sets. Individual wells have flowed 45 MBO from over 11,000’ prior to initiating artificial lift; atypical of Permian Basin reservoirs. Farther into the basin, the unit is consistently thick; however, the section is starved of siltstones and carbonates which are likely less productive reservoirs. Upslope the unit thins rapidly and becomes more gas-prone. In this setting the mixture of coarser-grained shelf carbonates and sandstones provided migration pathways breaching the closed system, limiting development of overpressure, natural fractures, productivity and economic ultimate recovery.

Since 2009, this play has been developed with vertical wells co-mingling the unconventional oil-resource with conventional reservoirs. Interpretation of imaging logs has identified the primary fracture orientation and zones with conjugate fractures systems. Integration with production logs has optimized horizontal target identification and horizontal drilling has begun. The Avalon, being exploited in New Mexico, is also present. The Avalon “sweet spot” occurs at similar depositional setting as the Wolfcampian resource and the same geographic position in this portion of the basin. The Avalon is estimated to have 103 MMBOIP per Section.