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DGGS gearing up for summer field work Investigations continue on North Slope, along the Alaska Highway corridor, around the Cook Inlet basin and near Slate Creek Alan Bailey Petroleum News
Geoscientists from Alaska’s Division of Geological and Geophysical Services are getting ready to pull out their boots, hammers and notebooks for another busy summer field season, progressing work programs in several areas of economic interest in different parts of the state. Sponsored by industry and the state, the DGGS research results in geologic data that can act as a framework for investigations by individual companies, and that can help businesses evaluate the economic potential of a region using public-domain information.
In April the division issued proposals, seeking industry sponsors for this year’s work.
North Slope program One DGGS-led team will head out in July for an area north of the Brooks Range, east of the Dalton Highway, continuing an investigation of a wide range of stratigraphic units in a region noted for oil seeps and other evidence of a petroleum system, and where some companies have been considering the possibility of drilling for natural gas, Robert Swenson, director of DGGS, told Petroleum News May 4. This year the DGGS team is moving north of what they refer to as the fold belt, along the northern side of the Brooks Range.
“They’re going to be focusing in on the Echooka and Ivishak Rivers, east of the Dalton Highway. … We’re moving to the north and away from the fold belt outcrop,” Swenson said.
The team will work in territory with excellent surface rock exposures where rivers have cut through the terrain. However, because of a lack of continuity of exposed rock between river valleys, the team will use seismic data to link together and make sense of the geology observed in the various isolated exposed rock sections.
In fact, the use of available seismic data to tie the surface geology into subsurface structures inferred from the seismic has become a major focus of the DGGS North Slope research. And the seismic data is enabling the geologists to link the geology observed at the surface to data from exploration wells drilled in the region.
“We’re … incorporating a significant amount of subsurface data that we’ve got access to now, including the wells,” Swenson said. “… That’s been really important to us to firm up some of our surface interpretations.”
New insights One result of this work will be a new geologic map of the Sagavanirktok River area that DGGS hopes to publish by the end of the summer, while the linking of surface and subsurface geologic data is providing new insights into the regional geology.
And, following what has become something of an annual tradition for the DGGS North Slope program, the division is organizing an industry show-and-tell, to be held on July 8 and 9. At this event, open to anyone who can arrange their own helicopter transportation, the North Slope team will take people on a tour of rock exposures that are important in piecing together the petroleum geology of the region.
“That’s something we’ve done every year now and that’s turned out to be a real learning experience for everybody, including us,” Swenson said. “Lots of people working a lot of different issues on the slope come, and there’s a lot of open discussion about the geologic interpretations that we’re seeing.”
Cook Inlet The Cook Inlet region forms another major focus for DGGS energy-related investigations.
In the latter half of May a Cook Inlet project team will head for the central west coast of the Inlet to examine what is termed the Mesozoic stratigraphy, the older of the two major rock sequences associated with oil and gas in the region. Although all of the existing Cook Inlet oil and gas fields have reservoirs in the Tertiary, the younger of the two rock sequences, the Cook Inlet oil originated from the older sequence — some geologists think that there is significant potential for a new oil find within the Mesozoic.
But people do not have a good handle on the subsurface distribution of the Mesozoic rocks, including potential reservoir rocks. That lack of information coupled with the high cost of drilling a deep well to penetrate the Mesozoic in the more central parts of the basin ups the ante on drilling risks.
So understanding the distribution of Mesozoic rock types will be a key to further oil and gas exploration in the Cook Inlet region, Swenson said.
“The long-term viability of exploration in the Cook Inlet certainly will revolve around the Mesozoic. (There is) short-term (interest), no question, in the Tertiary and the gas issues, but I think in the long term we’re going to have to have a better understanding of that Mesozoic than we do presently,” Swenson said. “… Any exploration effort that’s going to go on is going to benefit from having both an oil-leg part of it … as well as the shallow gas target.”
Iniskin Peninsula The DGGS team on the west side of Cook Inlet will be working in the area of the Iniskin Peninsula, where oil seeps were first discovered in the 19th century.
“Hopefully (they’ll) get in to see some of the (oil) source rocks and do some measured sections through that,” Swenson said.
The geologists also want to investigate the ways in which the rocks have become chemically altered, an issue of primary concern for the Mesozoic petroleum geology, since this alteration can result in the formation of minerals that clog the pores in rocks that would otherwise form good oil and gas reservoirs.
But, given the limited surface exposures of the rocks, DGGS wants to extract as much data as possible from the surface outcrops and then put the data into a geologic framework and a basin analysis, to extrapolate the data into the subsurface.
“Up to date it’s just been piecemeal here and there at getting the data, and there’s not a lot of real super-detailed data available, in the public realm anyway,” Swenson said.
Tertiary rocks The other component of the DGGS Cook Inlet research, an investigation of the Tertiary rocks of the Cook Inlet basin, began in 2006 with a primary objective of assembling information that will help explorers find subtle hydrocarbon traps, known as stratigraphic traps, that have generally been disregarded in the past but which the division thinks may contain much of the remaining undiscovered gas resources in the Cook Inlet basin. Gas deliverability issues from the Cook Inlet fields have been causing significant public concern.
“There is a lot of gas left in that basin, yet to be found,” Swenson said. “… This is our contribution to that effort to make sure that there’s gas in the Southcentral region for a number of years to come.”
DGGS has carried out detailed mapping, measuring and sampling of Tertiary rocks that outcrop along the shore and in sea inlets, in and around Kachemak Bay, towards the southern end of the Kenai Peninsula. The geologists are now trying to extrapolate the results of this work into the subsurface using seismic and well data, in a similar manner to what DGGS is doing on the North Slope.
“That’s really going to be the key for the east side (of the Inlet) and the stratigraphic traps that may be played there,” Swenson said.
Capps Glacier Later this summer a DGGS team will return to the Capps Glacier area, on the northwest side of the inlet, to continue an investigation of Tertiary rocks there, an investigation which began in the summer of 2008 but which was disrupted by bad weather.
The team is investigating the history and geometry of the Tertiary rocks deposited right on the northwest edge of the Cook Inlet basin, and determining the ways in which these rocks were deposited. In fact the Capps Glacier area has become a major focus for both DGGS and the U.S. Geological Survey, as part of the Statemap program, a program for developing detailed geologic maps with assistance from federal funds.
In addition, the geologists are looking for evidence for movement on the Castle Mountain fault that delineates the western margin of the Cook Inlet basin. An understanding of the history of fault movements can help with an analysis of the geologic hazards in the area and is especially important since the Castle Mountain fault extends east into the populated Wasilla and Willow areas, Swenson said.
“We’ve certainly seen some indication of recent (fault) activity,” he said.
An understanding of the fault history and fault system will also be of help to people exploring for geothermal resources in the nearby Mount Spurr geothermal leases, Swenson said.
Gasline corridor DGGS is also entering its final field season of a four-year program, mapping along the potential North Slope gas line corridor between Delta Junction and the Canadian border, primarily identifying geologic hazards, such as active faults and permafrost areas, and locating sites where construction gravel might be obtained. This summer’s project will involve mapping the corridor east of Tok, Swenson said.
“That’ll be the final leg of that 16-mile-wide corridor that we’ve been mapping,” Swenson said. “That’s been an incredibly fruitful effort for us. … We’ve identified some pretty major fault systems running through there that are currently active.”
By combining the fieldwork results with data from geophysical surveys, the division will be able to publish a detailed geologic map of the entire corridor, something that has not been done before. The data that DGGS has obtained will help determine design criteria for the pipeline, as well as provide information about where it may be possible to obtain construction materials, Swenson said.
DGGS staff is also involved in fieldwork associated with the eruption of the Redoubt Volcano on the west side of Cook Inlet. And a DGGS team plans to do some geologic field mapping northeast of Paxson in the Alaska Interior this summer, as part of a mineral investigation in that region.
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