Deadfall Syncline coal, quality and reserves

Abstract

PRESENT INVESTIGATION The purpose of the 1991 drilling program was twofold: 1. To evaluate the coal reserves in a previously identified thick coal in an area of low structural dips and dip-slope topography near the axial plunge of the west extension of the Deadfall Syncline, primarily for surface mining, and to determine the feasibility of mining additional beds in conjunction with the thick coal. (For the purposes of this investigation, this coal is designated K3 as explained below), 2. To examine a continuous and unbroken stratigraphic interval of the Corwin formation in the northeastern part of the Deadfall Syncline as an initial step toward evaluation of the whole basin. This was accomplished by drilling overlapping holes aligned generally parallel to the dip direction, and spaced in accordance with the magnitude of dip and depth capacity of the drill. About 720 feet of stratigraphic section were covered in this way. A total of fourteen exploratory holes were drilled, ranging from 116 to 426 feet in depth (Figure 2). The drill was a Mobil B-60 mounted on a Nodwell tracked vehicle. Circulation was provided by a large compressor mounted on another Nodwell. Most of the footage was drilled with an air hammer, which provided a significant improvement in drilling rates over conventional rotary drilling. Lithology of cuttings from all holes was logged continuously, and composite grab samples from each 5 or 10 foot interval were taken. Coal cuttings were collected on a (relatively) clean plastic sheet, and promptly double bagged in plastic to minimize loss of bed moisture. Cores were taken from the K3 coal at 3 drill hole locations, and the underlying K4 coal was also cored at one of these 3 holes. A comparison of core length to geophysical logs indicates essentially 100% recovery for all cores. All samples, including rock cuttings, were shipped to the Mineral Industry Research Laboratory (MIRL), University of Alaska Fairbanks, for analyses and/or storage. All holes were logged with a Gearhart-Owen GeoLogger using natural garmna and gammagamma density tools. The log response with these tools for coals is distinct and unambiguous, particularly that of the density log, and the resolution is sufficient to estimate bed thickness to within 3 to 4 inches (Figures 8 and 9).