gas hydrate - CCOP

Organic Geochemical Evidence for the Deep Gas Migration
and Mixing with CBM at Akabira Coal Mine, Hokkaido, Japan
Yuichiro Suzuki 1) , Tatsuo Maekawa 1) *, Shunichirou Igari 1) ,
Masami Yamaguchi 2) , Amane Waseda 3)
1) Geological Survey of Japan, AIST
2) Sumitomo Coal Mining Co. Ltd.
3) JAPEX Research Center
ABSTRACT: Previous research work on CBM gas compositions at several coal
mines in the Ishikari Coal-field in Hokkaido has indicated that all coal mines except
the Akabira Coal Mine have more than 99.5% of methane content in total
hydrocarbons.
From our results, Ethane (C2) and C 3 + light hydrocarbons contents ranged from
about 1% to 3% in Akabira CBM gas compositions. The 13 C carbon isotope
composition of the methane indicates that the methane is thermally generated and
not biogenetic. Gas compositions in each producing area in Akabira Mine show
that there is a greater contribution of deep gas in western part of the mine. The
geological map of the mine area indicates the presence of several faults with NNE-
SSW trends. It is inferred that deep gases migrated along several of the faults and
mixed with CBM in the coal seams.
Keywords: CBM, Akabira, gas composition, 13 C isotope
INTRODUCTION
The Akabira Coal Mine, in Ishikari Coalfield, Hokkaido (Figure 1), was operated by
Sumitomo Coal Mining Co. Ltd. from 1938 until it closed in 1994. The mine was well known
its abundant coal mine methane gas (CMMG). It has previously been reported that the C 2 +
component of the Akabira CMMG amounted to more than 1% of total hydrocarbon content
(Sasaki and Nagata shown in Suzuki et al., 2002). These results were very strange when
compared with CMMG from elsewhere in Ishikari Coal-field, including the Yubari and
Sorachi Areas, in Hokkaido. Here we report on several samples collected from the Akabira
Coal Mine area in 2003 and 2004 in order to clarify the origin of the Akabira CBM.
SAMPLES
Major coal seams at Akabira are of Paleogene age and comprise coal generally of bituminous
rank. The general geological structure of Akabira Mine is synclinal with several faults striking
NNW and dipping eastwards dip (Figure 2). CBM samples were collected at 5 localities; three
from the mouths of inclined shafts and two of vertical shafts. Their names and localities are
shown in Figure 2 and in Table 1. Arrows of sample localities in Figure 2 indicate the
downward directions of inclined shafts. The gas sample source areas in the No.3 inclined
shaft and in the Kamiuta vertical shaft are situated on the western limb of a syncline, and the
others are situated on the eastern limb.
New Energy Resources in the CCOP Region - Gas Hydrates and Coalbed Methane 159