Alaska North Slope shale resources: last Frontier has significant potential for unconventional oil extraction.

• Author: Stricker, Julie
• Position: SPECIAL SECTION: Petroleum Geology

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In 2012, the United States Geological Service (USGS) released a report that looked at the potential for oil and gas in three kinds of shale deposits found on Alaska's North Slope. The results were stunning.

According to the study's author, USGS Research Geologist David W. Houseknecht, the North Slope could contain up to 2 billion barrels of technically recoverable oil and 80 trillion cubic feet of natural gas. That ranks among the top source rock systems in the United States. The report came on the heels of successful shale oil and gas development in the Lower 48.

In terms of shale oil, that's second only to the Bakken Formation in Montana and North Dakota, as estimated by mean resource. The North Slope contains an estimated 940 million barrels of shale oil, compared with Bakken's 3,645 million barrels of shale oil. In mean estimates of undiscovered gas, the North Slope is fourth on the list of the five top fields. Its 42,006 billion cubic feet of gas is about half the largest, the Marcellus shale formation on the East Coast with 81,374 billion cubic feet. The others are Haynesville in Louisiana and Texas and Eagle Ford in Texas.

The study area includes all of the onshore areas north of the Brooks Range and the adjacent state waters. Shale deposits were found over nearly all the region, but two areas show no potential for shale oil, according to the survey. They were located on the northern tip of the National Petroleum Reservation-Alaska near Barrow and east of Prudhoe Bay, an area that includes northern edge of Alaska National Wildlife Reserve, which is believed to hold conventional oil and gas reserves.

Three Shale Varieties

The three varieties of shale were identified as Brookian shale, created during the Cretaceous period between 145.5 million and 65.5 million years ago; Kingak shale, laid down during the Jurassic period 199.6 million and 145.4 million years ago; and even older Shublik Formation, formed during the Triassic period 251 million to 199 million years ago.

These deposits generated the oil and gas that likely migrated to form the conventional oil and gas fields of Prudhoe Bay and Kuparuk, but no attempt has been made to produce oil or gas from the source rocks themselves. Limited oil production and gas tests from Shublik rocks are considered to be specific areas where the reservoirs allowed conventional accumulations of petroleum to occur.

The study notes that units considered to have high probability...