gas hydrate - CCOP

The analyses show that the coal from the drilled wells have an average specific gravity of 1.48,
moisture content of 16.2%, ash content of 24.2%, volatile matter of 27.56%, and fixed carbon
of 32.68%. The values of moisture content and fixed carbon are low because of high inorganic
content. The elemental analyses indicate that the coal is composed of 42.93% carbon, 4.14%
hydrogen, 1.55% nitrogen, 1.7% sulfur, and the heating value is 3461.15 calories per gram.
These values indicate that the coal from the Ma Lamao basin belongs to sub-bituminous to
bituminous rank according to the ASTM standard. It should be noted that high ash content in
the coal renders it of poor quality and the low carbon and hydrogen content may affect the
quantity of coalbed methane.
A coal petrographic study was conducted to determine the maturity of hydrocarbons. In
addition, types of marcerals, cleats, and pore space in coal are key factors that determine the
generation of coalbed methane. This study shows that the coal from the Mae Lamao basin
consists of marcerals belonging to vitrain. The majority of marcerals belong to the humunite
group, with subordinate liptinite, and rare inertinite. High amount of inorganic matter is
observed and is largely made up of pyrite and silica replacing former cell wall and pore space
in the coal. Vitrinite reflectance in oil (Ro) is 0.41% on average. The vitrinite reflectance of
the upper coal bed is lower than that of the lower coal bed, suggesting that the lower coal bed
has a higher coal rank than the upper coal bed, probably due to the effect of deeper burial. The
low value of vitrinite reflectance indicates that the depth of burial is relatively shallow and gas
and oil generation is immature.
The study of the cleat system reveals that the upper coal bed has more cleats and has less
mineral replacement than the lower coal bed. This allows the release of coalbed gases.
However, due to its low maturity, the flammable gases are present in only small quantities.
The lower coal bed is denser and is replaced by silica and pyrite that makes it relatively
impervious, obstructing the flow of adsorbed gases.
The study of small visible fractures in the rock and coal core samples from the production
well indicates only a small number (53) of fractures representing an intensity of 0.5 fractures
per 5 meter of core length. The majority of fractures is restricted to the depth of 170-260
meters and dip at high angles of between seventy and ninety degrees. These fractures are
associated with coal beds and the high dips suggest that these fractures are part of the cleat
system in the coal beds that facilitate an increase in the productivity of gases.
Quantity and properties of coalbed gases
Tests to determine quantity and properties of coalbed gases are considered to be the most
important step in the study to obtain accurate and precise data for assessment of commercial
coalbed methane development. Analyses of the quantity of methane gases is based on a
desorption test by replacement water in the canister with the released gases.
Procedures: An approximately 50 cm long core of coal was put in a canister as soon as
possible after removing it from the drill hole. The amount of time that had elapsed since the
coal was retrieved and removed from the drill together with the time taken to put coal into the
canister and close the canister lid was recorded. The canister was placed in a water bath and
the bottom temperature maintained at 39 degrees Celsius. For the first nine hours the amount
of gas released was measured every fifteen minutes using a gas flow meter system. The
measuring time was extended to120 days to obtain data for prediction of the gas production
rate.
New Energy Resources in the CCOP Region - Gas Hydrates and Coalbed Methane 139