Risk and Reserve Assessment: Lessons Learned from By-Passed Plays: Shongaloo Field, Louisiana, and Mission Canyon Play, North Dakota

William DeMis
Marathon Oil Company, Houston, TX

Discovery histories of Shongaloo Field (cum: 159 BCFG; 19.7 MMBO) and the Mission Canyon play (cum: 352 BCFG, 259 MMBO) provide a spectrum of lessons learned from by-passed fields to plays. Size and risk of by-passed fields and plays can be underestimated. By-passed fields can be underestimated because productive “dry holes” are not recognized. Plays can be by-passed if risk is underestimated and therefore too few wells are drilled; or if a few early, low-volume discoveries condemn the play as “uneconomic.”

Shongaloo Field is a 10-mile anticline located in the state line graben. The field was discovered in 1988 after three “dry” holes were drilled along the crest in 1954, 1972, and 1980. Reservoirs include Jurassic Smackover “B” carbonates, and siliciclastic “C” sand. Integrated well, core, and seismic data (and drilling 50 wells) revealed the field's size, which extended beyond and included early “dry” holes.

In the 1960s, Shell Oil Company drilled a dozen dry holes specifically targeting stratigraphic traps of the now-prolific Mississippian “Mission Canyon” play. Many of the now-known Mission Canyon dolomite fields have Shell wells offsetting them, or Shell “dry holes” in them. Shell's depositional model and seismic interpretation were perfect. However, Shell underestimated the play's risk, and therefore drilled too few wells to sufficiently test the play; and missed the pay in critical wells. When the play was discovered in the 1970's, operators still failed to recognize the enormous size of the fields, and did not lease sufficient acreage.