A native corporation evaluates potential of Alaska's Kandik area

David M. Hite
Consulting Geologist
Anchorage

Alaska's regional Native corporations control large tracts of land with significant mineral and hydrocarbon potential. One of these 12 corporations, Doyon Ltd., has extensive holdings with the potential for large oil and gas accumulations.

The most promising is the Kandik region of east-central Alaska ( Fig. 1 [51,034 bytes]). Recent compilations and research involving the organic geochemistry, stratigraphy, and timing of structural deformation in the Kandik area have resulted in much more optimistic appraisals of the oil potential.

These studies indicate that known oil-prone source units may have generated 50-100 billion bbl of oil. Some of these data have recently been made available to the public through the Alaska Division of Geological and Geophysical Surveys.^1-3

Exploration history

Geologic investigations commenced in the early 20th century,⁴ and petroleum exploration began in the early 1960s with mapping by Sinclair and Richfield in the area of the Step Mountain anticline. Additional exploration efforts were mounted by Louisiana Land and Exploration (LL&E) in the early 1970s and by ARCO Alaska Inc. in the 1980s and early 1990s.

LL&E drilled three wells into the Paleozoic carbonates northwest of the core Kandik area in 1976-77 (Fig. 1). The wells were dry but encountered porosity and bitumen in the carbonates.^5-6

ARCO, working under an exploration agreement with Doyon, conducted extensive geological, geochemical, and geophysical programs in the vicinity of the principal Doyon land holdings (Fig. 1). Due to the changing economic environment, ARCO allowed the agreement to expire prior to drilling in areas of primary interest.

Fig. 1 depicts the location of geophysical data sets in the Kandik area. Recent reports^1-3 provide data and general interpretations from these surveys and some of the subsequent studies. These reports include gravity maps, sampling stations, organic geochemistry data, and an example of a seismic test line (dip orientation) into the Nation River basin (Fig. 6 [60,801 bytes]).

Stratigraphy

The Kandik region has one of the thickest stratigraphic sections in Alaska, with rocks of Late Proterozoic to Cenozoic age. The cumulative thickness exceeds 40,000 ft and may be in excess of 50,000 ft.^{1 7}

The regional stratigraphy is summarized in Figs. 2, 3, and 4. The Proterozoic section (Fig. 2 [80,082 bytes]) consists of the Tindir Group, subdivided into upper and lower parts by an angular unconformity. The largely marine shales, sandstones, and carbonates, with associated tholeiitic basalts and red beds, are interpreted to represent either a simple rifted continental margin or a failed rift or aulacogen. Bitumen has been observed within the Tindir Group at three locations. The rocks of this sequence have excellent potential as seals and lesser potential as source rocks and reservoirs.

The Paleozoic succession (Fig. 3 [112,326 bytes]) is nearly 15,000 ft thick and ranges in age from Early Cambrian to Late Permian. Rocks of the Early Cambrian Funnel Creek limestone through the Middle Devonian McCann Hill chert were deposited in a passive continental margin setting. An unconformity at the top of the McCann Hill chert (Fig. 3) separates the Lower Paleozoic continental margin assemblage from the overlying Upper Devonian to Permian foreland basin sequence.

At Norman Wells in the western Northwest Territories of Canada a reefal development in the Key Scarp formation, an age equivalent of the Ogilvie formation, contains 600 million bbl of oil. The Norman Wells accumulation is sealed and sourced by the overlying Canol formation (Fig. 3). Four regional unconformities may enhance porosity, provide seals for stratigraphic traps, and act as detachment surfaces for Late Mesozoic thrusting.

The Mesozoic and Cenozoic (Fig. 4 [80,064 bytes]) are comprised of a thick series of rocks representing deep-marine to nonmarine deposition. The bulk of the Mesozoic assemblage was deposited in deep-marine environments. The uppermost Mesozoic and Cenozoic strata are of shallow-marine to nonmarine origin. The Triassic Glenn shale is an organic-rich condensed shale section equivalent to the Shublik formation of the North Slope and northwestern Canada. It has many of the characteristics of an oil shale and may have generated as much as 1.5 billion bbl of oil/cubic mile of rock.

Structure

Regional mapping reveals two episodes of compressional deformation and a younger extensional event associated with movements on the Tintina Fault system (Fig. 1). The Valanginian to Albian Cordilleran-trend event1 is not evident in the area of primary hydrocarbon potential, but the foreland basin that developed to the north of the Cordilleran deformation belt as the region subsided in response to thrust-loading is present there.

The Cordilleran structural belt and its foreland basin deposits were deformed during the Turonian/Campanian by the east-vergent Aklavik-trend thrust system, producing the large northeast trending folds and faults found in the Doyon acreage block (Figs. 1 and 6).

Extension on north-northeast trending normal faults and normal/dextral-oblique-slip on north-northwest trending faults is associated with the releasing bend on the right-lateral Tintina fault system. This system has been active from at least the Late Cretaceous to the present, with a probable displacement of 240-270 miles. The normal faults truncate and offset contractional structures and are kinematically related to the development of the Nation River basin (Fig. 6).

Hydrocarbon potential

The Kandik region was brought to the attention of the petroleum industry by the oil generation potential of the Glenn shale. While the Glenn shale is recognized as possessing the potential to generate large volumes of hydrocarbons and structures are abundant, there is concern regarding reservoir quality. Additionally, the maturation level and timing of generation and migration have been perceived as potential negatives. Resolution of these issues is critical to the successful evaluation of the region's oil potential.

Bitumen occurs at more than 20 locations, in rocks of Late Proterozoic to Cretaceous age, indicating the generation and migration of hydrocarbons. Geochemical studies8 show that source rock maturation level may be the most critical source rock parameter in the Kandik area.

Source rocks of the Nation River basin and Yukon thrust areas (Fig. 6) are in the oil generation window or are marginally immature for oil generation (Ro = 0.47-0.94%). The potential source rocks, lying to the north and west of the Nation River basin, have passed through the oil window and are now in the wet-gas and dry-gas windows or beyond (Ro = 1.63-3.48%), thus eliminating these areas from further evaluation. Fig. 5 [81,716 bytes] indicates the intervals that may have source rock potential within the Kandik area.

The five primary source rocks are the Glenn shale, Road River formation, McCann Hill chert, Ford Lake shale, and Calico Bluff formation. Each unit has zones in which the TOC exceeds 2.0 wt %, HI is greater than 300 (usually 500) mg/g, and S2 values range above 10.0 mg/g. Data supporting the Glenn shale as being the most prolific source are TOC content ranging to 7.0%, samples having HI values in excess of 1,000 mg/g, and the S2 values ranging to 78.72 mg/g.

Based on sparse data, the Adams argillite and Tahkandit limestone may have locally good to excellent source potential. The source potential of the Tindir Group is unknown. A common fetid odor in the stromatolitic limestone (Petl of Fig. 2) suggests the need for additional study.

While the exposed section lacks reservoir-quality rock, porosity has been reported from the Paleozoic carbonates of the subsurface.6 Several Paleozoic and Mesozoic units have lithologies that permit the development of good reservoir character under favorable depositional and burial (diagenetic) conditions (Fig. 5). The TKs map unit (Fig. 5) may provide local reservoirs in the Nation River basin, and units in the Tindir Group could develop reservoir quality porosity and permeability under appropriate conditions.

The best reservoir potential is believed to be in the Paleozoic carbonates. Several of these units contain vuggy porosity that is locally filled with bitumen and oil-stained. Typically the sandstone units are cemented by silica.

Prior to discounting these units as reservoirs, it is important to remember that, due to silica cementation, the major oil-producing intervals on the North Slope, at Prudhoe Bay and Endicott fields, have very low porosity and permeability in outcrop. Favorable depositional environments and diagenetic histories have preserved and/or developed world-class reservoirs in units that appear to have no reservoir potential in surface exposures.

Numerous compressional and tensional structures, plus stratigraphic traps, are present in the Kandik area (Fig. 5). Compressional structures are of pre-, syn-, and post-thrust origins.

Structures include those formed in the frontal foot-wall fold-belt, internal to the thrust-plate, foot-wall imbricates with associated folds, and folds resulting from interference between the Cordilleran and Aklavik deformation fronts. Other structures are caused by extensional faulting (Fig. 5) associated with displacements on the Tintina fault system.

Stratigraphic traps are expected to be common, especially in the clastic-rich sections and where carbonates grade laterally and vertically into deepwater shale and chert sequences. Virtually any stratigraphic trapping scenario, from sub-unconformity truncation to stratigraphic pinchouts and channeled sandstones to carbonate dissolution and fracture traps, may be expected to occur in the area (Fig. 5).

At least five stratigraphic intervals have the characteristics of good oil seals. These are the Adams argillite, Road River formation, Ford Lake shale, Glenn shale, and Biederman argillite (Fig. 5). Each is dominantly an argillite or shale, has an areawide distribution, and is not significantly breached by erosion. Other formations may provide local seals (Fig. 5) but are prone to fracturing.

The mere existence of the key elements of a petroleum system: source rock, reservoir, and trap/seal is not sufficient to guarantee the accumulation of a sizable volume of hydrocarbons. The timing of the generation and migration of hydrocarbons relative to the formation of traps and the conduits to these traps is critical. In the Kandik area, oil generation is probably related to the episode(s) of major thrusting and concurrent thickening of the stratigraphic section in the Late Mesozoic (Fig. 5). These events buried the prospective source rocks to depths of 10,000-15,000 ft and resulted in maturation levels in or near the oil-generation window. Live oil seeps and measured present-day thermal maturities indicate that oil generation and migration continue to the present.

Prospective areas

Recent evaluations focus attention on the Nation River basin and Yukon thrust areas (Fig. 6). Dictating this focus are: source rocks of excellent quality, thermal maturities in the oil window, numerous oil seeps (bitumen) associated with the source rocks, and a block of highly prospective Doyon land (Fig. 6).

Two distinct and independent prospective areas are recognized.

The Nation River basin (Fig. 6) contains a thick Tertiary and Cretaceous (TKs) clastic section that rests unconformably upon the primary targets, the Paleozoic carbonates in the upper plate of the Nation River thrust.1 The thrust plate overlies the excellent source rocks of the Glenn shale that outcrop around the margins of the basin in both the upper and lower plates. Gravity reveals a series of northeast trending syn-thrust structural highs in the deformed rocks of the upper thrust plate. Secondary targets are in the Devonian and Tertiary-Cretaceous clastics.

The Yukon thrust play (Fig. 6) straddles the Alaska-Yukon border and consists of lower plate Paleozoic reservoirs overlain and sealed by Proterozoic rocks of the upper plate. This is a higher risk play than the Nation River basin play. There is greater difficulty in defining structures with gravity in the lower plate, and the play is dependent upon oil sources other than the Glenn shale. However, fair to excellent source rocks are present in the Paleozoic section. Paleozoic carbonates are believed to represent the best reservoir targets, with secondary objectives in the Paleozoic clastics. Surface oil seeps (bitumen) at the margins of the Yukon thrust indicate that oil generation and migration has occurred beneath the thrust. The lack of oil seeps internal to the Yukon thrust, except along major faults, implies that the fine-grained clastics of the Tindir Group may act as a seal for subthrust reservoirs.

Both the Nation River basin and the Yukon thrust plays occur largely within the limits of the large Doyon Ltd. acreage block of Fig. 6. This provides interested parties with relatively unencumbered access to a number of attractive exploration opportunities without the need to work through highly structured and frequently litigation-prone state and federal leasing processes.

References

Van Kooten, G.K., Watts, A.B., Coogan, J., Mount, V.S., Swenson, R.F., Daggett, P.H., Clough, J.G., Roberts, C.T., and Bergman, S.C., Geologic investigations of the Kandik Area, Alaska and adjacent Yukon Territory, Canada, Alaska Division of Geological and Geophysical Surveys, Report of Investigations 96-6a, 1996, 3 sheets, scale = 1:125,000.
Van Kooten, G.K., Watts, A.B., Coogan, J., Mount, V.S., Swenson, R.F., Daggett, P.H., Clough, J.G., Roberts, C.T., and Bergman, S.C., Station locations in the Kandik area, Alaska and adjacent Yukon Territory, Canada, Alaska Division of Geological and Geophysical Surveys, Report of Investigations 96-6b, 1996, 1 sheet.
Van Kooten, G.K., Watts, A.B., Coogan, J., Mount, V.S., Swenson, R.F., Daggett, P.H., Clough, J.G., Roberts, C.T., and Bergman, S.C., Gravity maps of the Kandik area, Alaska and adjacent Yukon Territory, Canada, Alaska Division of Geological Surveys, Report of Investigations, 96-6c, 1996, 1 sheet, scale = 1:250,000.
Cairnes, D.D., The Yukon-Alaska international boundary between Porcupine and Yukon Rivers, Canada Geological Survey, Memoir 67, 1914, 161 p.
Di Bona, P.A., and Kirschner, C.E., Geological bibliography for selected onshore sedimentary basins of central and southern Alaska, stressing basin analysis and including an index of available well and subsurface data, U.S. Geological Survey, open file report OFR 84-99, 1984, 70 p.
Hite, D.M., and Nakayama, E.M., Present and potential petroleum basins of Alaska, in proceedings of the Southwestern Legal Foundation, Exploration and economics of the petroleum industry, Vol. 18, 1980, pp. 511-560.
Schaff, R.G., Gilbert, W.G., Lindberg, F.A., Childs, O.E., Steele, G., and Salvado, A., Northern Alaska region, AAPG, Correlation of stratigraphic units of North America (Cosuna) project, 1987, 1 sheet.
Underwood, M.B., Laughland, M.M., Wiley, T.J., and Howell, D.G., Thermal maturity and organic geochemistry of the Kandik basin region, east-central Alaska, U.S. Geological Survey, open file report OFR 89-353, 1989, 41 p.

The Author

David Hite is an Anchorage consulting geologist. He has over 30 years' experience in exploration, much of this with ARCO in Alaska. Under direction of James Mery, Doyon Ltd. vice-president of lands and natural resources, Hite undertook an extensive review and re-evaluation of Kandik area petroleum geology and hydrocarbon potential. Doyon, an Alaska Native corporation based in Fairbanks, is Alaska's largest private landowner with about 12.5 million acres. Much of this, including the Kandik area, is held in fee simple ownership. Its subsidiary, Doyon Drilling Inc., operates five rigs on Alaska's North Slope. Another affiliate, Doyon Universal Services, provides catering, security, and camp maintenance. E-mail: [email protected]