Cook Inlet Basin Research Articles

Developments in Alaska in 1966

Exploration and development in Alaska during 1966 reached maximum activity. Exploratory drilling resulted in 5 new-field discoveries, 1 new-pool discovery, and 6 successful extensions out of 36 wells drilled. Success was limited to the Cook Inlet basin and the discovery rate decreased from 52% in 1965 to 30% in 1966. Particularly important was the confirmation of the McArthur River field as a giant oil field comparable to Swanson River, Middle Ground Shoal, and Granite Point. Seismic activity increased 31% from 1965. Extensive joint marine surveys were conducted in the Bristol Bay, lower Cook Inlet, and the Gulf of Alaska. Surface geological parties increased 17% from 1965. The Gulf of Alaska and Arctic Slope were the most active basins. State competitive lease sales in the Cook Inlet basin and the Gulf of Alaska brought a total bonus of $7,177,160 for 152,577 acres. The Department of the Interior opened 4,000,000 acres on the Arctic Slope for simultaneous filing. Leasing was slowed by native land claims on approximately 60% of the land area of Alaska. Development drilling increased slightly; 9 oil wells were completed in offshore fields of Cook Inlet. Oil production increased 29% from 1965 to 14,358,212 bbls., and gas production increased 244% to 41,217,032 Mcf. In Cook Inlet 4 new drilling and production platforms were added to the 2 already in operation to drill the vast new offshore oil reserves. Five more platforms, to be erected in 1967, will provide a combined capacity of 400 wells. Dual pipelines 39 mi. long were laid to connect these new platforms to onshore facilities. Laying of a 20 in., 42-mi. pipeline began along the west shore of the Inlet, and will connect the developing west-side fields to a tanker terminal at Drift River. Ground was broken on the Kenai Peninsula near Nikiski for an ammonia-urea plant. The Kenai gas ield will provide the methane feedstock. The shut-in Beluga River gas field is expected to produce gas in 1967 to generate onsite electrical power for transmission to Anchorage.

Developments in Alaska in 1965

Exploration in Alaska during 1965 was highlighted by the high success of exploratory drilling. Nineteen exploratory wells were drilled with 52.6% successful oil or gas completions. Seventeen exploratory wells were drilled in the Cook Inlet basin and 10 were successful. Alaska's 5 new-field discoveries were made in this basin, and for the first time oil discoveries were made on the west shore of Cook Inlet. Exploratory drilling is expected to increase in the Cook Inlet basin during 1966 and to continue on the Arctic slope. Geological surface work and geophysical activity decreased during 1965. A marked increase in both is expected during 1966, particularly in geophysical activity in the Cook Inlet basin. It is anticipated there also will be an increase in the Gulf of Alaska and in Bristol Bay. Activity on the Arctic slope is expected to continue at the same rate or to increase slightly. State land sales on the Arctic slope and in Cook Inlet resulted in bonus bids of $10,819,816. Two large blocks of Federal land were released on the Arctic slope. Leasing activity is expected to remain high in 1966. The first oil production from the Middle Ground Shoal field in Cook Inlet was marketed through a newly completed offshore pipeline. Six more pipelines are expected in Cook Inlet in 1966. Development drilling accelerated with the development of the Kenai gas field. Two development wells were drilled in the Middle Ground Shoal field and development drilling in this field is expected to increase greatly during 1966.

Significant Oil and Gas Developments in Alaska, 1965-1966: ABSTRACT

Recent oil exploration in Alaska is centered in five sedimentary basins: Cook Inlet basin; Arctic (North) Slope province; Bristol Bay basin; Gulf of Alaska province; and Copper River basin. Surface and seismic exploration parties have been active in each, greatest emphasis being in the Cook Inlet basin and the Arctic (North) Slope province. The oil industry in Alaska during 1965 drilled 19 exploratory wells, resulting in the discovery of 3 oil fields, 3 gas fields, and extensions of 2 oil fields and 1 gas field. The 3 oil discoveries, all under Cook Inlet waters, are Granite Point, Trading Bay, and McArthur River. The gas discoveries are on the upland area of the Cook Inlet basin at Birch Hill, North Fork, and Moquawkie. The Granite Point discovery was extended north more than 3 mi. by subsequent drilling. A discovery was made 6 mi. south of production at Middle Ground Shoal. Gas production at the Cook Inlet field was extended about 2 mi. southwest. Two exploratory wells drilled in 1965-66 on the Arctic (North) Slope were reported non-productive. Two shallow dry exploratory wells were drilled on the north flank of the Co per River basin. Both were unsuccessful. The first two permanent platforms in Cook Inlet were installed at Middle Ground Shoal oil field during 1965, and development drilling began. A twin 8-mi. crude-oil pipeline was completed connecting the two platforms with an onshore treating facility. This furnished the first outlet for crude oil other than that at the Swanson River field. Contracts were let for 6 additional offshore-drilling and production platforms to be erected during 1966. End_Page 2029------------------------------ The most significant event since the discovery of oil in the Lower Kenai Conglomerate (Hemlock) at Swanson River was the discovery of multiple-pay sandstone beds in the Middle Kenai Formation. These sandstone beds furnish an additional objective and have higher porosity and permeability than the Lower Kenai Conglomerate. Gas pay zones have been found in both the Middle Kenai and Upper Kenai sandstone zones. End_of_Article - Last_Page 2030------------

OIL FIELDS AND AEROMAGNETIC ANOMALIES

Six examples of relationships between aeromagnetic anomalies and producing areas are presented by maps of subsurface structure, observed aeromagnetics, second vertical derivatives of the aeromagnetic fields, and maps of the magnetic basement computed from the aeromagnetic data whenever all these are available. In addition, a copy of an original aeromagnetic traverse is included. The examples embrace Puckett in the Delaware Basin of West Texas, Grieve in the Wind River Basin of Wyoming, Tioga and Onstad in the Williston Basin of North Dakota, Swanson River in the Cook Inlet Basin of Alaska, and Zelten in the Sirte Basin of Libya. These include both “before and after” examples with basement maps prepared in some cases before discoveries, and in other cases afterwards. The paper purports to demonstrate that correlative magnetic anomalies exist in either event. Moreover, these anomalies would be disclosed by any competent technique, so techniques of interpretation are not a part of the argument. It is well known that the larger observed aeromagnetic anomalies result from intrabasement contrasts of magnetization. Anomalies resulting from structure alone ordinarily are smaller by a factor of the magnitude of ten. Of the six cases, Puckett, Tioga, and Onstad represent structures with associated intrabasement effects, whereas anomalies at Grieve, Swanson River, and Zelten are considered to be purely structural effects. There are difficulties involved in using either type of anomaly quantitatively for determination of depth to basement and the relief of possible basement structure. But these examples are part of a much larger amount of evidence which seems to justify improving the definition of the observed aeromagnetic field so that the small residual structural effects can be better defined in order to find more of them and to interpret them more accurately. New instrumentation with higher sensitivities is now available for this second venture in aeromagnetic prospecting.

The U. S. Geological Survey's program of Alaskan gravity observations

The U. S. Geological Survey began gravity surveys in Alaska in 1958. About 700 observations were made along the highways and on the shores of major lakes in the area covered by the Copper River aeromagnetic survey. During the following years the gravity measurements were extended to include parts of the Alaska Range and Tanana Valley, and they have gradually evolved into a program designed to prepare a reconnaissance gravity map of the whole state within the next five years.Before the surveys began, published data from gravity surveys in Alaska consisted of records from (1) about 6000 stations obtained in a 26,000‐square‐mile area of northern Alaska, Naval Petroleum Reserve 4, by the U. S. Navy and by United Geophysical Corporation [Woolson, 1962]; (2) about 500 widely scattered stations observed by members of the University of Wisconsin [Thiel et al., 1958; Woollard et al., 1960]; (3) a few traverses near Prince William Sound by the Carnegie Institution of Washington [Tatel, 1956]; and (4) some control stations established by the U. S. Coast and Geodetic Survey [Rice, 1958]. Petroleum companies had already made surveys (unpublished) of the Bethel basin, Nushagak basin, Cook Inlet basin, Yakataga geosyncline, and some other possible petroleum areas.

Developments in Alaska in 1964

Exploration in Alaska continued at a high level during 1964 with emphasis placed on the Cook Inlet basin and on the Arctic slope. More than nine crew-years of geophysical work were completed in seven Alaska basins or geologic provinces. The opening of new State and Federal lands for leasing on the Arctic slope has stimulated exploration in this area. Twenty-three exploratory wells were drilled during 1964, resulting in the discovery of two new gas fields, one new-pool extension of gas, and one new-pool extension of oil. Three of the discoveries were located in the Cook Inlet basin and one on the Arctic slope. State and Federal competitive land sales in 1964 resulted in offers of more than $17 million in bonuses for lands located primarily in the Cook Inlet basin and the Arctic slope. Exploration in the Copper River basin continued at a low rate and little exploration interest was shown in other interior basins in 1964. Development drilling is expected to increase during 1965 from the low of two completed wells in 1964. Exploration is expected to continue at 1963-64 levels during the coming year.

Developments in Alaska in 1963

The most important thing that happened in 1963 was the discovery of oil by Shell et al. under the waters of Cook Inlet. Tests indicate producing capacities of at least 600 bo/d are possible. This is the first real encouragement the industry has seen insofar as oil is concerned since Swanson River was discovered in 1957. The second most important thing that occurred was the high level of exploration on the Arctic Slope. Five seismic crews operated during the year and a sixth was moving in at year's end. Ten operators did 29 crew-months of surface geology during the summer. Exploratory drilling decreased to 18 wells this year. Several of these were suspended for the winter and will presumably become active again in 1964. The seismograph continues to be a popular tool in the Cook Inlet where more than 4 crew-years of work were done. This work will undoubtedly manifest itself at future lease sales and in exploratory drilling. The Copper River basin seems to be going through a period of renewed interest by drilling, seismograph, and surface exploration. Two wells were completed and a third started. Three seismic crews were active and three operators had surface crews in the basin. Exploratory activity in the other basins was not spectacular. It remained constant, but at a low level in some and decreased in others. Over-all exploration for the state should increase the next few years, particularly in the Cook Inlet basin and on the Arctic Slope. The Bristol Bay and Copper River basins will probably be actively explored but not to the intensity anticipated elsewhere.

Developments in Alaska in 1962

During 1962, 23 exploratory wells were drilled compared with 20 in 1961. Development wells decreased from 29 to 13. First offshore drilling commenced in 1962 from 2 barges and 1 platform in Cook Inlet basin and from 1 platform along the Alaska Peninsula. Offshore drilling in Cook Inlet was discontinued in November due to winter ice but will be resumed in early, spring. First wells were drilled on the west side of Cook Inlet. Three new gas fields were discovered during 1962 and 1 offshore gas blow-out was burning. No oil fields were found. A seismic crew was air-lifted to the Arctic (North) Slope and shooting commenced in the area east of Naval Petroleum Reserve No. 4. This is the first seismic work in the area since the U. S. Navy Department discontinued exploration in 1953. Seismic mapping increased from 73¼ crew-months in 1961 to 81¼ crew-months in 1962 with all of the increase due to offshore sparker-gas exploder work. Surface geologic exploration decreased 25.9%. An increase in surface geologic work and also seismic activity is expected in 1963. The Arctic (North) Slope is to receive the greatest increase. Exploratory drilling may show a slight decline and development drilling a continued decline.

Cook Inlet Basin--Structure, Stratigraphy, Exploration Techniques, Logistics, Discoveries: ABSTRACT

Exploratory objectives in the Cook Inlet Basin are confined largely to the Kenai Formation, a 15,000-20,000-foot series of non-marine, coal-bearing sediments of Eocene or younger Tertiary age, underlain by marine Mesozoic sediments. The Kenai Formation on the Kenai Peninsula is divisible into an upper sand member, a middle siltstone and coal member, and a lower sand member. The gas fields on the Kenai Peninsula occur in the upper member; Swanson River oil production is from the lower member. The Kenai beds have been gently to moderately folded and locally faulted. Exploration techniques consist of surface mapping, gravity and airborne magnetometer surveying, and reflection seismic shooting. Marine reflection shooting and gas exploder-sparker surveys have been used to explore Cook Inlet. Some structural leads can be obtained by field mapping but seismic work is needed to confirm closure. To date only structures defined by seismic methods have been drilled. The Swanson River oil field is producing in excess of 28,000 barrels per day from the Hemlock zone, a series of sands and conglomerates near the base of the Kenai Formation. The structure is a large, faulted anticline. Five gas fields have been discovered--the Kenai, Swanson River, West Fork, Falls Creek, and Sterling fields. Gas from the Kenai field is being delivered to Soldotna and Anchorage; the other fields are shut in although some gas from the Swanson River gas field is used in oil-field operations. The gas consists of 99% methane and is believed to have originated within the Kenai Formation. There is insufficient evidence to determine whether the oil originated in the Kenai Formation or in underlying Mesozoic shales. Seismic crews cost between $60,000 and $85,000 per month. Costs of deep exploratory wells on the Kenai Peninsula vary between $20 and $50 a foot, exclusive of road costs. Completed oil wells in Swanson River cost nearly $400,000. Road costs range from $10,000 to $50,000 per mile. An increase in the tempo of exploratory drilling in 1962 is indicated. End_of_Article - Last_Page 271------------

General Geology and Hydrocarbons of Cook Inlet Basin, Alaska: ABSTRACT

The Cook Inlet basin of south-central Alaska is an intermontane structural basin approximately 14,000 square miles in area, encompassing almost 80,000 cubic miles of sedimentary rocks ranging in age from upper Triassic to Recent. The basin coincides with most of the northern part of the Matanuska geosyncline, an arcuate Mesozoic trough located at the northwestern end of the Pacific Cordilleran mobile belt. The Cook Inlet sedimentary trough, in contrast to the structural basin, is defined as a Paleozoic-early Mesozoic eugeosyncline that received sediments from emergent volcanic islands which were part of the volcanic archipelago belt bordering the Pacific Coast of North America. Middle Jurassic epeirogeny transformed southern Alaska into arcuate geanticlinal and geosynclinal belts with the Cook Inlet basin beginning as a half-graben created by complex faulting on the east flank of the Talkeetna geanticline. The Mesozoic embayment that collected marine sediments and occasional non-marine wedges abutting cratonic source areas was semi-enclosed or silled as the Kenai and Chugach ranges began to emerge following the early stages of the Laramide orogeny. During the early Tertiary, an abundant supply of non-marine clastic sediments and carbonaceous material was widely distributed in the subsiding intermontane basin. The structural grain of the major tectonic elements describing the basin architecture is preserved in trends of local structure throughout the basin. Intense folding and faulting are exhibited on the north, east, and west flanks of the basin. Several major buried anticlinal trends extend in a northeasterly direction through the interior of the basin. Mesozoic hydrocarbon accumulations associated with anticlinal traps are found on the western side of the basin. Minor quantities of oil, gas, and condensate have been produced from sandstones of the middle Jurassic Tuxedni formation. The oil is believed to be indigenous to Jurassic beds, the exact age and position of which are questionable on the basis of present-day stratigraphic relations. Oil and gas accumulations in Tertiary beds will determine the significance of the Cook Inlet basin as an oil and gas province. Present oil production comes from the Hemlock zone, a distinct sandstone and conglomerate unit near the base of the Tertiary Kenai formation. Entrapment has been influenced by folding and faulting along trend of an interior basin high which lies adjacent to and parallel with an early Tertiary hinge belt. The Tertiary crudes were probably derived from Eocene marginal marine strata or from upper Cretaceous marine shales which are unconformably overlain by the Tertiary sediments. Significant quantities of gas, predominantly methane, are present in the loosely consolidated sands of the upper Kenai formation. The two conditions necessary for gas accumulation anywhere in the basin are (1) abundance of lignite or coal beds in the section to serve as source rocks, and (2) a suitable trap. The Cook Inlet basin is in its earliest stage of exploration and development. It is anticipated that many new oil and gas fields will be discovered. Regional isopach maps of the interval between the Mesozoic beds and the base of the Hemlock zone are suggested as a basic approach to delineating old basin highs that may be sound Hemlock prospects. The Cook Inlet basin should become a major gas basin regardless of its future as an oil province. End_of_Article - Last_Page 419------------

AN AEROMAGNETIC PROFILE FROM ANCHORAGE TO NOME, ALASKA

A total‐intensity profile was obtained on a 500‐mile flight by a U. S. Geological Survey airplane from Anchorage to Nome, Alaska, on May 4, 1954. The average flight altitude was 6,000 ft above sea level except over the Alaska Range where the flight altitude was 9,000 ft. This profile crossed eight of the major tectonic elements of Alaska at right angles to their trend and gives valuable regional information in an area where other geophysical and geological information is scarce or lacking. The profile has a net gradient downward to the northwest, most of which is ascribed to the component of the earth’s main magnetic field along the flight traverse. The great variety of magnetic anomalies which are superimposed on this gradient originate from variations in lithology along the traverse. All the magnetic anomalies, except a large one over the Yukon River, are caused by magnetic rocks at or near the surface. The magnetic profile may be divided into four major segments and nine subsegments, each having a characteristic magnetic pattern. Most of these can be related to a tectonic unit. The large plutons of the Talkeetna geanticline are clearly defined by a group of anomalies having the highest amplitudes of any on the profile. The Matanuska geosyncline to the east is represented by a 25‐mile section of sloping profile consistent with a thick sedimentary section but indicating that the geosyncline is comparatively narrow near Anchorage. The 200‐mile central magnetic segment is relatively free from all but very minor anomalies. This segment includes the Alaska Range geosyncline, the Tanana geanticline, and the Kuskokwim geosyncline; showing only slight magnetic contrasts between each of these elements. The two geosynclines either have thick Mesozoic sedimentary sections or have underlying crystalline rocks which are low in magnetic susceptibility at shallow depths. The rocks of the geanticline have a low but not negligible magnetic susceptibility and are predominantly Paleozoic sedimentary rocks. A single 300‐gamma anomaly on the west edge of the central segment is caused by a small, mafic intrusive body in the Paleozoic metamorphic rocks of Mt. Hurst. West of this anomaly the profile consists of a series of small sharp anomalies which are probably caused by Paleozoic metavolcanic rocks of the Ruby geanticline. The second largest anomaly on the profile is in the Koyukuk geosyncline over the Yukon River. The source is calculated to be more than a mile deep and may be an intrusive body at least 15 miles wide. This anomaly is flanked by 20‐mile sections of flat or sloping profile which indicate areas of thick sedimentary rocks, particularly in the region west of the Yukon River. The 150‐mile Norton Sound magnetic segment on the western end of the profile consists of many closely spaced anomalies produced by rocks which are either volcanic or similar to the Seward complex. Of the four Cenozoic basins or lowlands crossed by the profile, three are underlain by rocks of moderate to high magnetic susceptibility at shallow depths. These are the Cook Inlet basin, part of which overlaps rocks of the Talkeetna geanticline, the Innoko basin of central Alaska which overlies the rocks of the Ruby geanticline, and the Norton basin, in which sedimentary deposits are thin or absent. The fourth, the Minchumina basin, is underlain by the low‐susceptibility rocks at the Tanana geanticline, which are also probably close to the surface.

Developments in Alaska in 1957

The Territory of Alaska comprises more than 600,000 sq. mi. Increasing interest in the northern and central provinces as well as the southern province developed in 1957. The northern province, including the Arctic coastal plain, has been withheld from public entry as Naval Petroleum Reserve No. 4 and by Public Land Order No. 82. The U.S. Department of the Interior has recently announced lands withheld under P.L.O. No. 82 will be opened in 1958. The central province including the Porcupine, Koyukuk, Bethel, and Nushagak regions is in a very early stage of exploration. Acreage leased in these regions by the end of 1957 probably exceeds 10 million acres. Surface geological investigations during 1957 totaled 21 party-months and seismic and magnetometer surveys 6 party-months. The southern Alaska province includes the Copper River, Cook Inlet, Alaska Peninsula, and St. Elias-Coastal regions. Drilling activity increased 4-fold in 1957 over 1956. The total footage drilled in 1957 was 52,480 ft. as compared with 15,168 ft. in 1956. Drilling in the Cook Inlet basin resulted in a major discovery that may develop into the first substantial commercial production in Alaska. In the Copper River basin no new activity except leasing took place in 1957. Total filings in the basin were approximately 2 million acres. In the Cook Inlet basin the Richfield Oil Corporation's Swanson River Unit No. 1 was completed for 900 b/d from 11,150 to 11,215 ft. in Tertiary sands. The well was located on the basis of seismic and surface data and is the first deep test in the basin. Following the discovery, competitive lease activity ensued and leases or applications to lease cover the basin. In the St. Elias-Coastal region the Phillips Petroleum Company and Kerr-McGee Oil Industries, Inc. abandoned their Sullivan No. 2 as a dry hole at 12,048 ft. and terminated their development contract with the U. S. Department of the Interior. The Colorado Oil and Gas Corporation abandoned its Yakutat No. 1 at 9,314 ft. and at the end of the year was drilling ahead at about 10,500 ft. on its Yakutat No. A-1. Nearly all of the accessible land in this region was leased or under application. In the Alaska Peninsula region Iniskin Unit Operator, Inc. tested its Beal No. 1, total depth 9,746 ft., and received oil and gas indications. The Humble Oil and Refining Company and Shell Oil Company's Bear Creek Unit No. 1 was drilling at 6,586 ft. at the end of the year. About 3 million acres were leased or under application in the region. Exploration in Alaska is expected to increase sharply in 1958 over 1957.