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September 2018

Vol. 23, No.35 Week of September 02, 2018

Results from Doyon/CIRI Totchaket. Nenana basin well not commercial

Alan Bailey

Petroleum News

The Totchaket No. 1 exploration well, drilled in the Nenana basin this summer by Doyon Ltd. and Cook Inlet Region Inc, encountered multiple gas shows but did not find commercial oil or gas, CIRI has reported. CIRI said that, based on drilling results conducted so far in the basin, it continues to view the basin as holding considerable resources.

Drilling of the Totchaket well, on the east side of the Tanana River, about 20 miles north of the town of Nenana, began on June 6 and ended on July 5. The well has since been plugged and abandoned. According to data published by the Alaska Oil and Gas Conservation Commission, the well was drilled to a vertical depth of 11,225 feet.

Multiyear program

Doyon has been conducting an oil and gas exploration program in the Nenana basin for a number of years - CIRI has partnered with Doyon in the drilling of both the Totchaket well and the previous well drilled in the basin, the Toghotthele well, drilled in 2016. The basin is conveniently located close to the Parks Highway, to the southwest of Fairbanks. Recently Doyon has been particularly focusing on making an oil discovery, although the basin is also highly prospective for natural gas.

The Nenana basin, one of a number of Alaska basins formed by the pulling apart of the Earth’s crust, is filled with a huge thickness of non-marine Tertiary sediments. Coal seams and shales within the rock sequence have the potential to source both oil and gas, depending on the extent to which they are heated at depth. There are sands with excellent hydrocarbon reservoir potential, interlayered with shales that could form hydrocarbon traps. In broad terms, the basin has a northeast to southwest trending hourglass shape, with a deep basin in the north and a central saddle in the narrower, central part of the basin, immediately west of the town of Nenana. The depths reached in the northerly section of the basin are thought to be sufficient to have raised the temperatures in the potential source rocks to levels conducive to oil formation.

Three previous wells

Doyon and partners have previously drilled three wells in the basin’s central saddle, targeting potential traps identified from seismic data. The hope was that hydrocarbons migrating up into the saddle from deeper parts of the basin would have become trapped. Although these wells failed to discover viable pools of oil or gas, the wells did encounter evidence of an active petroleum system. The Toghotthele No. 1 well, for example, drilled in 2016, found multiple oil shows, as well as natural gas. Some of that gas was “wet gas,” containing natural gas liquids that must have formed through the application of heat rather than through microbial action on organic material. But it seems that what now appears to be a trapping structure had formed after the oil had migrated through the rocks.

The Nunivak No. 1 well, drilled in 2009, also encountered some oil shows. And the Nunivak No. 2 well, drilled in 2013, found a 400-foot thick section of gas-bearing rock that also contained too much water to be commercially viable.

Focus on northerly prospects

With the drilling of the Totchaket well, attention shifted to the deeper more northerly part of the basin, above the presumed oil and gas kitchen. The well targeted the Totchaket East prospect, one of five prospects identified from 3-D seismic data collected from a survey conducted in 2017. Apparently the seismic displayed hydrocarbon indicators in all of the prospects. And the mapping of subsurface rock units, using seismic and gravity data, suggests that the northern part of the basin may have more reliable hydrocarbon migration pathways than farther south, with an absence of the uplift that may have disrupted hydrocarbon trapping mechanisms in the central saddle.

- ALAN BAILEY






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