Naknek formation findings published

Alaska’s Division of Geological and Geophysical Services has published the results of fieldwork and geologic studies conducted by geologists from DGGS and Alaska’s Division of Oil and Gas, investigating the upper Jurassic Naknek formation, exposed in the Iniskin Peninsula and Tuxedni Bay area on the west side of the Cook Inlet.

The Naknek has some oil and gas reservoir potential in the sparsely explored Mesozoic sequence of the Cook Inlet basin. Producing oil and gas fields in the basin have reservoirs in the more extensively explored younger and shallower Tertiary sequence. But geologists view the Mesozoic as also having potential for new oil and gas discoveries.

Of particular note in what the state geologists found during their research was evidence of large, ancient submarine canyons in the Naknek. These canyons had become filled with sediment, including much sand. The Naknek was deposited in a marine environment adjacent the uplifted roots of an ancient volcanic arc. Evidence from the nature of the rocks indicates cycles of deepening and shallowing water.

The minerals within the rocks tend to be prone to decomposition to clay materials that can clog pore spaces, thus, when buried, liable to degrade the rocks’ permeability and porosity. However, the state geologists think that oil and gas exploration can benefit from the insights that the state research can provide into the depositional systems involved in forming the Naknek and where the best hydrocarbon reservoir quality may be found - knowledge of the systems can provide an understanding the reservoir quality variability and possible oil charge timing.

- ALAN BAILEY