Dallegge, Todd A.¹, C.E. Barker²
(1) ConocoPhillips, Houston, TX
(2) U.S. Geological Survey, Denver, CO

ABSTRACT: Update on Coalbed Methane Desorption Results from the Kenai Peninsula, Cook Inlet Alaska

Live coal cuttings sampled from recent infill drilling at the Kenai (KBU 42-7 well) and Beaver Creek Gas Fields (BC-10 well) as well as the Ninilchik Unit (Grassim Oskolkoff -1 well) show that Cook Inlet Basin coals contain gas contents (the cuttings data corrected to a coal core equivalent basis) of 20 to 300 scf/ton (dry, ash-free basis). These subbituminous to bituminous rank coals were sampled in the lower Sterling, Beluga, and Tyonek Formations ranging in depth from 775 to 4880 total vertical depth subsea (TVDss). Isotopic analyses of gas samples taken during desorption indicate a dry gas dominated by methane of biogenic origin (-52 to -64 d13C). These data are consistent with previous samples taken from the basin.
Proximate analysis of the lower Sterling and upper Beluga coals from the Kenai and Beaver Creek Fields have high ash yields (14-34 wt.-%) and consequently, may locally show low permeability because of poor cleat development. Isotherm analyses indicate the coalbeds gas contents range from saturated to undersaturated in the samples from the producing fields. The undersaturated coals may reflect partial depletion of the coalbed gas by coproduction in the conventional gas field.
Lower Beluga and Tyonek coal cuttings samples from the Grassim Oskolkoff -1 well (Ninilchik Unit) suggest relatively high methane contents (100-300 scf/ton d.a.f.) between 3000 and 4500 ft (TVDss). Coal ash yields are low over this range (5-12 wt.-%) suggesting potential for good cleat development and consequently higher coalbed permeabilities. Isotherm analyses are currently being analyzed. This well was drilled from an onshore location to an offshore location near Ninilchik, AK. The results from this well indicate that there are potentially significant coalbed methane reserves onshore in the Ninilchik area.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.