Migrated hydrocarbons in exposure of Maastrichtian nonmarine strata near Saddle Mountain, lower Cook Inlet, Alaska
Alaska Division of Geological & Geophysical Surveys Report of Investigation 2012-1
- D.L. LePain, P.G. Lillis, K.P. Helmold, and R.G. Stanley
Magoon and others (1980) described an 83-meter- (272-foot-) thick succession of Maastrichtian (Upper Cretaceous) conglomerate, sandstone, mudstone, and coal exposed on the south side of an unnamed drainage, approximately 3 kilometers (1.8 miles) east of Saddle Mountain in lower Cook Inlet (ﬁgs. 1 and 2). The initial signiﬁcance of this exposure was that it was the ﬁrst reported occurrence of nonmarine rocks of this age in outcrop in lower Cook Inlet, which helped constrain the Late Cretaceous paleogeography of the area and provided important information on the composition of latest Mesozoic sandstones in the basin. The Saddle Mountain section is thought to be an outcrop analog for Upper Cretaceous nonmarine strata penetrated in the OCS Y-0097 #1 (Raven) well, located approximately 40 kilometers (25 miles) to the south–southeast in Federal waters (ﬁg. 1). Atlantic Richﬁeld Company (ARCO) drilled the Raven well in 1980 and encountered oil-stained rocks and moveable liquid hydrocarbons between the depths of 1,760 and 3,700 feet. Completion reports on ﬁle with the Bureau of Ocean Energy Management (BOEM; formerly Bureau of Ocean Energy Management, Regulation and Enforcement, and prior to 2010, U.S. Minerals Management Service) either show ﬂow rates of zero or do not mention ﬂow rates. A ﬂuid analysis report on ﬁle with BOEM suggests that a wireline tool sampled some oil beneath a 2,010-foot diesel cushion during the ﬂ ow test of the 3,145–3,175 foot interval, but the recorded ﬂ ow rate was still zero (Kirk Sherwood, written commun., January 9, 2012). Further delineation and evaluation of the apparent accumulation was never performed and the well was plugged and abandoned.
As part of a 5-year comprehensive evaluation of the geology and petroleum systems of the Cook Inlet forearc basin, the Alaska Division of Geological & Geophysical Surveys obtained a research permit from the National Park Service to access the relatively poorly understood ‘Saddle Mountain exposure’ that is located in the Lake Clark National Park and Preserve. This work was done in cooperation with the Alaska Division of Oil & Gas and U.S. Geological Survey (USGS) research geologists. This report expands on Magoon and others’ (1980) description of the exposure, presents new data on sandstone composition and reservoir quality, presents new geochemical data on petroleum extracted from the outcropping sandstone, and describes oil-bearing correlative strata penetrated by the Raven well. Although the exposure is more than a kilometer (0.6 mile) east of Saddle Mountain (ﬁg. 2), in this report we variously refer to it as the Saddle Mountain succession, Saddle Mountain section, or the rocks at Saddle Mountain underlain by Upper Jurassic strata of the Naknek Formation.
Additional publication details
- Publication type:
- Publication Subtype:
- Other Government Series
- Migrated hydrocarbons in exposure of Maastrichtian nonmarine strata near Saddle Mountain, lower Cook Inlet, Alaska
- Series title:
- Alaska Division of Geological & Geophysical Surveys Report of Investigation
- Series number:
- Year Published:
- Alaska Division of Geological & Geophysical Surveys
- Contributing office(s):
- Geology, Minerals, Energy and Geophysics Science Center
- iii, 13 p.
- United States
- Other Geospatial:
- Cook Inlet;Saddle Mountain