Stratigraphic Framework and Petroleum Potential of Mesozoic Strata on the Ugashik Creek Anticline (Pearl Creek and Hubbell Domes), Southeast Side of Becharof Lake, Alaska Peninsula

Blodgett, Robert B.
[email protected]

This talk presents a review of the geologic framework, stratigraphic setting, source rocks and potential reservoirs associated with the Ugashik Creek anticline, a prominent NE-trending structure in the NE ¼ of the Ugashik Quadrangle, near the SE end (Island Arm) of Becharof Lake. The Ugashik Creek anticline, including the Pearl Creek Dome at its northern end and the Hubbell Dome at its southern end, is an extremely promising structure in terms of future petroleum development. Based on the prominence of oil seeps along its anticlinal crest, it was tested in the early 1920’s with five cable tool drilled wells (Lee #1, Lathrop #1, McNally #1, Alaska #1, and Finnegan #1). Most of the wells were for the most part relatively shallow and none reached either the Kialagvik or Kamishak Formations which are identified here as being the primary targets (nonetheless oil and gas shows were noted in the well bores). The deepest well (Lee #1 of Standard Oil Company of California) reached T.D. at 5,034 ft (1,534 m) in the middle part of the upper Middle Jurassic Shelikof Formation. Upgrading of the road system built from Kanatak to the Pearl Creek Dome oil field in the 1920’s also makes this area attractive in terms of having an existing infrastructure already in place. The region has not been open to exploration for the past few decades, but the recent acquisition to subsurface drilling rights in this area by Koniag, Inc., makes it again a viable target.

The presence of numerous oil and gas seeps in Jurassic rocks of the northern part of the Alaska Peninsula (Puale Bay-Becharof Lake-Wide Bay region) clearly indicates that a widespread petroleum system is present at relatively shallow depths. The Upper Triassic Kamishak Formation at Puale Bay has long been considered the primary source horizon for hydrocarbons in the region. To the north this same unit was considered until the past few decades to be the probable source for oil seeps on the Iniskin Peninsula in Lower Cook Inlet. Recent study of source rock potential of the Puale Bay region (Decker, 2008) indicate that both the Upper Triassic Kamishak and the essentially Middle Jurassic Kialagvik Formation are organic-rich and make excellent oil-prone source rocks. Both stratigraphic units are found throughout much of the northern Alaska Peninsula in the subsurface, and probably underlie the Ugashik Creek anticline.

Identification of reservoirs at depth during drilling must be seriously addressed by future explorationists. Given the emergence of new drilling technology (i.e., directional drilling, hydrofracking) further attention should be focused on rich source bed units such as Upper Triassic Kamishak Formation and early Middle Jurassic Kialagvik Formation as drilling objectives for oil shale/oil gas plays. The 2,000 ft+ thick Kamishak Formation (several order times thicker than the time-equivalent Shublik Formation of the North Slope – the prime source horizon there) makes it an excellent target for exploration. The Kialagvik Formation is slightly less organic-rich than the Kamishak, but still has respectable TOC (total organic carbon) values. The latter unit is also deemed a good target in light of the fact that its age equivalent in the Cook Inlet basin, the Middle Jurassic Tuxedni Group, is considered to be the primary source for Cook Inlet oil (Magoon and Anders, 1992).

The Ugashik Creek anticline has many features indicating which suggest the Upper Triassic-Middle Jurassic succession would make an excellent target for an oil shale/shale gas play. The baseline geologic framework of surface exposures is now relatively well understood, but much remains to be done with understanding the region in the subsurface. Shooting 3-D seismic would be critical in better understanding the structural setting at depth. In addition, drilling activities should pay critical attention to the stratigraphic and age interpretation of strata encountered in the well bore, as this particular issue has held back proper interpretation of what strata were being drilled during earlier operations in the region. Detailed paleontological analysis of microfossils (Radiolaria, pollen and spores) from cuttings (and any core) should be done as quickly as possible in order to determine correct age and formation assignments.

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013