SOCIE?I’YOF PETROLEUMENGINEERSOF AIME 6200 North CentralExpressway *R SPE 1588 Dallas,Texas 752C6 THIS IS A PREPRINT--- SUBJECTTO CORRECTION Geological Characteristics in Cook Inlet Area, Alaska Downloaded from http://onepetro.org/SPEATCE/proceedings-pdf/66FM/All-66FM/SPE-1588-MS/2087697/spe-1588-ms.pdf by guest on 25 September 2021 By ThomasE. Kelly,Jr. MemberAIYE, Mickl T. Halbouty,Houston,Tex. @ Copyright 19G6 Americsn Institute of Mining, Metallurgical and Petroleum Engineers, Inc. This paper was preparedfor the 41st AnnualFall Meetingof the Societyof PetroleumEngineers of AIME, to be held in Dallas,l?ex.,Oct. 2-5, 1966. permissionto copy is restrictedto an abstract of not more than 300 words. Illustrationsmay not be copied. The abstractshouldcontainconspicu- ous acknowledgmentof whereand by whom the paper is presented. Publicationelsewhereafter publica- tion in the JOURNALOF l?i’TROI.WJMTECHNOLOGYor the SOCIETYOF PETROLEUMENGINEERSJOURNALis usually grantedupon requestto the Editorof the appropriatejournalprovideciagreementto give propercredit is made. Discussionof this paper is invited. Three copiesof any discussionshouldbe sent to the Societyof PetroleumEngineersoffice. Such discussionmay be presentedat the abovemeetingand, with the paper,may be consideredfor publicationin one of the two WE magazines. v, The Cook Inlet basin is a narrow, Although the general characteristics elongate trough of Mesozoic and Ter- of the basin are fairly well known, tiary sediments located north of new information, as it is made avail- latitude 59° in south-central Alaska able will cause many revisions of the (Fig. 1). The basin covers approxi- stratigraphic and structural fabric mately 11,000 square miles of th~ before a complete geological picture northerripart of the Matanuska geo- is possible. This report revises syncline and is bounded by the Kenai and refines certain concepts of the and Chugach Mountains”on the east, basin which were discussed in an the Talkeetna Mountains and the earlier work (Kelly, 1963). In cer- Copper River on the northeast, the tain aspects it may be considered q Susitna basin on the north, the progress report that will require Chigmit Mountains and the Alaska periodic updating”as new information Range on the west , and the Shelikof is made available. Strait on the south. In less than ten years the basin PREVIOUS WORK has achieved su.@ a degree of promi- nence as a pet~’oleumprovince that A list of references includes many it ranks with’bff-shore areas in published reports wri~ten chiefly by California and the Gulf Coast as the members of the U. S. Geological Sur- most promising future source of large vey who investigated the mineral re- domestic reserves. sources of the Cook Inlet basin. The Oil and gas exploration in the first indications of petroleum in basin has rapidly increased in the the basin and the early attempts to past few years and is currently at find production were documented by its highest level in history. Martin (1905). Ma&her (1925), fur- ther described the petroleum poten- References and illustrations ac end tial of the southwestern part of the of paper. basin in the Kamishak Bay area. Miller, Payne and Gyrc (1957), pre- TRIASSIC ROCKS sen~ed the first comprehensive in- vestigation dealing specifically with Paleozoic and early Mesozoic’sedi- potential petroleum provinces of mentation occurred in a linear de- Alaska which included the Cook Inlet pression that occupied most of south- Mesozoic and Tertiary basin. Ayres ern Alaska. Volcanic islands and (1959), discussed the regional Tee- archipelagos, emergent throughout tonic framework of the basin as re- the belt, served as loca. .)urcesof lates to preorogenic and postorogenic sediments and provided areas for Downloaded from http://onepetro.org/SPEATCE/proceedings-pdf/66FM/All-66FM/SPE-1588-MS/2087697/spe-1588-ms.pdf by guest on 25 September 2021 units of the circumpacific geanti- reef limestone deposition. Bedded clinal and geosynclinal evolution cherts comprising a large part of (Kay, 1951). Parkinson (1962), pre- the Triassic System were probably sented the first field paper on the precipitated from volcanic silica basin’s first commercial oil field, and deposited contemporaneously with the Swanson River field. Other work- tuffaceous silts, shales and carbon- ers have recently contributed to the ates. knowledge of the complex stratigraphy Areal Extent and LithologY - Tri- and s~ructure of the basin (Kelly, assic rocks have been identified on 1961, 1963; Hill, 1963). Information the southeastern rim of the basin on the basin architecture was pro- near the town of Seldovia and on the vided by an aeromagnetic study of the western coast of Cook Inlet in the region by Grantz, Zietz, and Andrea- vicinity of Kamishak and Bruin Bays. son (1963). The excellent palyno- The Triassic rocks in the Kachemak logical studies of Wolfe, Hopkins and Bay region include limestone, tuff, Leopold (1965), provided much needed and banded chert, underlain by el- stratigraphic information on the lipsodial lava, slate, and graywacke nonmarine Tertiary rocks of the basin. which may be pre-Triassic in age. The Halbouty Alaska Oil Company STRATIGRAPHY Fritz Creek {/1well located a few miles eastof Homer on the north shore Rocks of Triassic co Recent age of Kachemak Bay penetrated several crop out in the Cook Inlet basin - hundred feet of white platey chert those older than Tertiary, are ex- which is considered to be equivalent posed in scattered localities on the in age to the surface exposures near ~rimeter of the basin, A general- Seldo”~ia. The total thickness of ized correlation chart of the basin the Triassic System in the Cook Inlet is shown in (Fig. 2). Mississippian basin probably exceeds 2000 fee~. and Permian sediments are exposed in a belt trending northwestward through JURASSIC ROCKS the southern Copper River basin and the slate-graywacke sequences com- The Jurassic rocks of southern prioin~ the Kenai-Chugach Ranges, al- Alaska, including the Cook Inlet though generally considered to be of basin, represent the most complete Upper Cretaceous ages may contain sequence of this age on the North Paleozoic rocks, (Martin, Johnson and American continent. The theater for Grant, 1915; Smith, 1939; and Ayres, Early Jurassic sedimentation was 1959)● similar to the Late Triassic, al- The maximum thickness of post-Paleo- though a hiatus of undetermined size zoic sediments deposited in.the deep- is reflected by a period of nonde- est part of the basin is estimated to position at the close of the Triassic. be 40,000 feet. Exploratory drilling During the Middle Jurassic, epeiro- has penetrated an aggregate of 30,000 geny transformed the paleozoic-early feet of sediments ranging in age from Mesozoic sedimentary trough into ge- ‘UpperTriassic to Recent. anticlinal and geosynclinal belts. The Tertiary rocks are discussed in Diastrophism renewed valcanic acti- greater detail in this paper because vity, and batholiths and lesser in- of their economic significance. trusive were emplaced on the north and west sides of the basin. The Naknek-Chinitna contact has been de- Cook Inlet basin became a dynamic scribed as conformable by most writ- structural basin and occupied approxi- ers; however, Barnes and Payne (1956] mately its present position. report the Naknek was deposited on Areal Extent and Lithology - An the eroded surface of older Jurassic unnamed section of Lower Jurassic formations, rocks is exposed on the southwestern Upper Jurassic marine clastic coast of the Kenai Peninsula in the rocks consisting of argillite and A thick se- green-gray siltstone, have been pene- vicinity of Seldovia. Downloaded from http://onepetro.org/SPEATCE/proceedings-pdf/66FM/All-66FM/SPE-1588-MS/2087697/spe-1588-ms.pdf by guest on 25 September 2021 quence of Lower Jurassic volcanic trated in wells drilled on the Kenai rocks known as the Talkeetna Form- Peninsula, off-shore Cook Inlet, and ation is exposed in the upper Mata- Susitna Flats. The rocks appear to nuska Valley and adjacent mountains be greatly altered in comparison to and has been penetrated in a few the surface sections exposed in the boreholes on the east side of the southwes~ern shore of the basin and basin. Middle and Upper Jurassic no direct surface-subsurface corre- sediments comprising the Tuxedni, lation has ye~ been published. Chinitna, and Naknek formations are widely distributed along the south- CRETACEOUS ROCKS western shore of Cook Inlet and in the upper Matanuska Valley. Early Cretaceous time w~ascharac- The Lower Jurassic rocks of the terized by shallowing of the seas Seldovia area consist predominately and local emergence reflected by of tuff and volcanic agglomerates. areas of erosion or nondeposition The unit is not fossiliferous but is along linear structural belts. lithologically similar, and perhaps Areal Extent and Lithology - Upper partly equivalent in age, to the Cretaceous rocks are exposed in Talkeetna Formation. The Talkeetna the Matanuska Valley along the Mal- formation is composed of volcanic keetna Mountain front, in the Chugach detritus containing fossil plants Mountains north of Turnagain Arm, and and marine invertebrates. The base in the extr,smesouthwestern part of of the formation has not been ob- the basin on the Alaska Peninsula served but the total thickness is es- south of Kamishak Bay. These rocks timated to be several thousand feet. have been encountered in several The Middle Jurassic Tuxedni Form- wells drilled on the eastern side of ation consists of sandstone, shale, the basin on the Kenai