Environmental Information for Outer Continental Shelf Oil and Gas Decisions in Alaska (1994) / Chapter Skim
Currently Skimming:
3 Geological Setting and Hydrocarbon Resource Base
3 Geological Setting and Hydrocarbon Resource Base
Pages 41-66
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From page 41... ...
Along the margin of the Beaufort Sea, its width from the shoreline to the slope break at a water depth of 200 m ranges from 70 to 160 km. West of Point Barrow it widens into the broad Chukchi shelf, a triangular region about 500 On on a side.
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From page 42... ...
Inc., 1991. The shelf is the geological extension of the North Slope of Alaska and is underlain by a variety of sedimentary strata, including many formations Hat constitute source rocks and reservoir rocks for petroleum and natural gas.
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From page 43... ...
Quaterna~ Pleistocene (Glacial) Plio ene Miocene TeHia ~Oligocene Eocene Paleocene Ore aceous Jurassic Triassic 0.01 1.8 2.8.
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From page 44... ...
and the probable extension of many of these formations suggest that the North Slope of Alaska and the adjacent continental shelf contain large reserves and that this region will continue to be explored and developed for some time. The similarity of the geology of the North Slope to several over passive continental margins adds to our confidence in this interpretation.
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From page 45... ...
· OIL FIELD ~T DEPOSITIONAL GAS FIELD ~ UNCONFORMITY OIL AND GAS ~ EROSIONAL Fi£LD ~L UNCONFORMITY ,-. ., ~ SANDSTONE SHALE CONGL OMERATE ~ LIMESTONE ARGILLITE ~DOLOMITE FIGURE 3-2 Generalized lithostratigraphic column showing the relationship of onshore rock units in northern Alaska to offshore seismic sequences in the Beaufort Sea Planning Area.
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From page 47... ...
Source: Adapted from Thom~s etal.,l991. ~ 72 e ~East Oc South ~ Barrow Barrow \ Barrow l 158 Beaufort Sea '49 ;:,eai Point Gwydyr Island Mcintyre x~G Barrow Barrow Sandpiper \ | /Prudhoe / Point Thomson |
From page 48... ...
To Be south and southeast the province is bordered by Be Herald Arch and Be seaward extension of Be Brooks Range (MMS, 1989~. The Chukchi Sea province is composed of Tree primary sedimentary basins: the Colville Basin, the Central Chukchi Basin, and Be Norm Chukchi Basin.
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From page 49... ...
The Cretaceous to Tertiary Brookian section is composed, onshore and offshore, of deltaic sediments derived from the Brooks Range to Me south. Geochemical studies from onshore areas show that the Ellesmerian and Brookian sections contain source rocks that could provide significant quantities of of!
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From page 50... ...
Source rocks were identified; particularly the Shublik Formation of the Ellesmerian sequence. High-quality reservoir rocks were not as widespread as had been hoped.
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From page 51... ...
The sequence is generally present on He Arctic Platform and He Nuwuk and Kaktovik basins, but is missing to He north in the Arctic Basin. Because He Ellesmerian section produces most of the oil in He North Slope fields, He areas where these sediments are present are considered to be the most promising for of} exploration.
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From page 52... ...
Excellent source rocks have been identdfied in the Ellesmerian section of wells in Alaskan state waters and onshore. Prudhoe Bay Field, the largest oil field in North America, and its surrounding fields left no doubt that oil was generated and entrapped in Be province.
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From page 53... ...
Similarities with the Atlantic continental margin of the United States are many and striking. The North Slope and the adjacent continental shelf, slope, and rise are correctly identified in MMS reports as being "Atlantictype." Although climate has imposed an unusual and harsh surficial environment, the general geology of the Beautort-Chukchi OCS is neither strange nor unusual.
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From page 54... ...
The discovery, which is in OCS Sale 87, is currency estimated at ~ billion barrels of recoverable oil, a figure consistent wig MMS's preliminary estimate. Indicative of its very conservative approach, MMS will not significantly revise its estimates for the Beaulort despite this discovery, because only one well has been drilled to date.
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From page 55... ...
The committee concluded that He geological data base is adequate for the purpose of lease sales, but that the lack of adequate geological summaries in the EISs makes it difficult for other disciplines, such as oceanography and biology, to use the information in attempting to assess the potential impacts of OCS exploration and production. 12LSOUI2C~ ASS[SSMI:~ITS Several analyses of the petroleum resources of the Alaska OCS region, and of the Chukchi Sea and Beaufort Shelf basins in particular, reveal a potential for future supplies.
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From page 56... ...
The benchmark estimates were those prepared by MMS and included in the 1989 report of the Department of the Interior, "Estimates of Undiscovered Conventional Oil and Gas Resources in the United States A Part of the Nation's Energy Endowment" (USGS/MMS, 1989~. MMS's estimates come from continuing studies by the service that use a sophisticated computer-based probabilistic method called PRESTO (Probabilistic Resource Estimates-Offshore)
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From page 57... ...
Source: USGS/MMS, 1989. Table 3-3 Quantitative Estimate of Total Oil Potential for Beautort and Chukchi Crude Oil, Bbbl Natural Gas, TCF 5% 5% Mean Probability Mean Probability Beaufort Shelf 11 30+ 15 65+ Chukchi Seas 4.3 21.7 15 73 ~ aThe approximate 50% discounting of the values for the Chukchi Sea is based on Be assigned 0.5% risk that hydrocarbons will not be present in the region.
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From page 58... ...
Committee on Undiscovered Oil and Gas Resources produced an evaluation of the Department of the Interior's 1989 assessment procedures used in assessing the nations resources of of} and gas (NRC, 199Ib)
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From page 59... ...
One possible deficiency, common to several MMS offices, was a dearth of geochemical studies related to source rock abundance, organic carbon types, and thermal maturity. Methods The NRC Committee on Undiscovered Oil and Gas Resources found fault with several aspects of the way in which data and geological judgment were incorporated into the PRESTO model that is used to estimate resources.
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From page 60... ...
Specifically, this committee was asked to focus on the adequacy of resource information made available in EISs and SIDs (secretarial issue documents) associated wig lease sales.
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From page 61... ...
PRESTO effectively considers interrelated risks and input data in a simulation process that reflects the needs of industry for exploration in developing an estimate. If environmental scientists are to make comparable analyses, it win be necessary to continue or expand the simulation process to include quantification of both the likelihood and the magnitude of a variety of risks.
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From page 62... ...
Because these studies are not only required but also are essential to protect equipment and personnel, industry will pursue them thoroughly. Investigations in and around a drill site or production facility concern foundation stability, including the likelihood of slumping, the presence of subsea permafrost and gas hydrates, and physical properties of the formations.
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From page 63... ...
The report noted also that the arctic seafloor poses special engineering challenges and that Were are subject areas in which more information is needed. Seafloor conditions that wall greatly influence the design and economics of offshore activities include thaw subsidence (associated with the presence of subsea permafrost)
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From page 64... ...
The geology of the Chukchi and BeauLort seas is reasonably well known and adequately discussed in MMS's final EISs. No additional regional studies of the seafloor in die vast Arctic region are warranted und} drilling sites are selected.
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From page 65... ...
Additional infonnati~n that would assist environmental scientists in quantifying risks should be released arm included in ElSs. Alternative: Call attention to the geological reports that address Me potential size and distribution of of!
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