Hilcorp’s “modern exploration toolbox” has paid off, with the resultant natural gas discovery at the Seaview prospect near the town of Anchor Point slated for production later in 2020, Hilcorp Senior Geologist Dave Buthman said in a presentation to the Alaska Geological Society March 17.
“We’re going to be drilling new wells and putting Seaview pad online this year,” he said.
The Seaview No. 8 discovery well was completed in December 2018 to a vertical depth of 10,148 feet.
Buthman said Hilcorp employed modern airborne gravity gradiometry and magnetic surveys, along with geologic field surveys, drainage anomaly studies and seismic surveys to hone in on more optimized well locations in its search on the Kenai Peninsula and upper Cook Inlet for more gas to serve Cook Inlet area markets.
The company is also exploring in the lower Cook Inlet and on the Iniskin Peninsula to evaluate oil and gas potential in that area.
Buthman said Hilcorp is working on bringing the Seadrill West Epsilon jack-up rig to the inlet to drill prospects such as the Blackbill prospect in the lower inlet next year.
According to Seadrill specifications, the West Epsilon, built in 1993, has harsh water experience in the North Sea. It has a maximum drilling depth of 25,591 feet and can operate in a maximum 393.7 feet of water.
ARCO drilled the Raven No. 1 well in the Blackbill prospect in 1982. The well lies about 40 miles west of the town of Homer.
Beware ‘line of death’
Traditional Cook Inlet oilfield lore warned of a “line of death” that crossed Cook Inlet south of the City of Kenai, south of which a commercial discovery was highly unlikely, Buthman said.
Before 2000, 32 wells and 6,000 miles of seismic below the dreaded line had not proven the warning to be untrue.
But in 2000, concerns of a natural gas shortage in the Cook Inlet region moved Unocal and Marathon to cross the line searching specifically for gas, discovering the Ninilchik field, and several others.
In 2012 Chevron/Unocal sold, and in 2013 Marathon sold, their producing properties in Cook Inlet to Hilcorp, which continued the quest.
“Ninilchik was found first, and then Happy Valley, Cosmo and now Seaview near Anchor Point,” Buthman said. “Always go outside the box.”
A modern box of tools
Hilcorp has reached into a box of modern - and not so modern - tools to bolster its success.
“Basically, the main oil horizons in Cook Inlet are the Eocene, West Forelands, Hemlock and Lower Tyonek," Buthman said, adding that the big gas zones are the Sterling, the Beluga and down to the Middle Tyonek.
Hilcorp teams have visited and studied key outcrops in the basin, observing the Sterling at Ninilchik Bluff, uppermost Beluga at Diamond Gulch and Tuxedni source rocks at Fossil point.
The company has also studied surface geology and seeps.
“The first structure that was drilled in the Cook Inlet has not produced commercial oil yet; we hope to change that,” Buthman said, adding that in the big breached anticline at Iniskin, three wells were drilled from the early 1930s up till the late 1950s, which “found various amount of oil there.”
“Basically, back at the turn of the century to about the 1930s people would map these surface structures on horseback, etc. looking for oil seeps,” he said. “We actually acquired seismic data though here in 2013 and we found a number of crestal seismic shot holes had filled with oil, so it’s an interesting feature, it’s just not at commercial production yet.”
Drainage anomalies have provided important clues as well.
Soldotna Creek, for instance, wraps around the main producing part of the Swanson River field.
“It’s hard to avoid seeing the importance of drainage anomalies when you see this,” Buthman said. “A full half of the production of Swanson River has come from this circular drainage anomaly.”
Happy Valley has a nosing drainage anomaly where Deep Creek flows that reveals a surface expression of the structure, he said.
“The discovery we just made at Seaview, you see the same sort of thing with the Anchor River,” he said. “We don’t have outcrops there, but we still see the same nosing.”
Hilcorp has found success using modern gravity gradiometry to correct seismic data for velocity issues.
The company takes seismic and traces the reflectors and inputs density data from the wells.
“You end up with a cross section which is a density solution of seismic traced time contours,” Buthman said.”
The process then employs a combination of observed gravity, and calculated gravity.
“After you trace the seismic lines, we have to work these polygons until we get a match between the observed and the calculated,” Buthman said.
“It’s interesting that when you get up on the hinge areas of folds, when you get low density material, which ... means you have low velocity - kind of a tipoff you might have gas sitting there,” he said.
“We take the density control from the model, invert that for velocity, and then we go back to our time data, and correct it.”
Finally, the company looks at selected drill wells.
“There were 166 wells drilled in Alaska prior to the first commercial discovery at Swanson River; the smartest people in the world from the biggest oil companies in the world had drilled 166 wells in the state before the first commercial discovery,” Buthman said.
“Before the really Big Kahuna was found - Prudhoe Bay - there were a total of 567 wells drilled ... so this a humbling exercise how long it really took and what stick-with-it it took.”
In locating the Seaview discovery well, Hilcorp drilled 600-foot stratigraphic test wells using a water well rig.
“We logged them, correlated them, mapped them, and we drilled our discovery well: Seaview No. 8,” he said.
Lower Cook Inlet
Buthman said Hilcorp is working 3D seismic data it acquired in the fall of 2019 in lower Cook Inlet, and the company has taken some exploration licenses offshore at Iniskin.
The seismic has produced some prospects, notably the Blackbill prospect, where early interpretations from seismic reveal a “beautiful four-way structure ... it’s a 65,000 acre beautiful four-way closure with an oil discovery on top; we kind of like those sort of things.”
“We’re working on it; the only issue is it’s shallow, and that’s why ARCO really didn’t develop it at the time,” he said.
Buthman said Blackbill will be the first Cretaceous commercial production in the Cook Inlet basin.
Relatively nearby, the Iniskin is another interesting but challenging prospect.
“Why we liked it was … we don’t like the reservoir, nobody does, but what we like is you’ve got about 9,000 feet of source rock there, right along the Bruin Bay fault in a similar structural position to the largest oil field in the basin which is McArthur River - which made about 650 million barrels of oil so far. That was our analog there.”
Buthman said the Zappa No. 1 well, drilled there in the 1950s, had big gas shows and tested from 100 barrels per day to 400 bpd from the Tuxedni.
