Petroleum Technology News
Second Publication 2002
and KGS Expand Coalbed Methane Research and Services
With the recent publishing of the Tertiary Oil Recovery Project's
(TORP) manual "Fundamentals of Coalbed Methane Production",
and current field research and testing by the Kansas Geological
Survey (KGS), the state's coalbed methane industry is being provided
with a new and continuing source of engineering and geological
support and information. The TORP manual is intended to provide
the operator of midcontinent coalbed methane wells with a practical
document which provides information concerning:
- the properties of coal
- the occurrence of natural gas in coal,
- reservoir engineering characteristics of coalbed methane
- drilling, completing and equipping coalbed methane wells,
- developing and managing the coalbed methane prospect from
defining the geology to marketing the gas.
The manual is available for $20 and an order form is included
in this newsletter.
The Kansas Geological Survey in cooperation with companies
active in the area has undertaken a research project to evaluate
the coals of eastern Kansas. The project is a broad based resource
assessment of coalbed gas in eastern Kansas and western Missouri.
Since the early 1980s, natural gas has been intentionally
produced from coalbeds. Spurred on initially by significant tax
credits, this sub-industry has grown rapidly in recent years,
now contributing in excess of 5% (1 tcf) of the nation's natural
gas production. The term "coalbed methane" (CBM) is
derived from the coal mining industry, describing the gas which
is a common hazard in coal mining operations. Methane typically
comprises 95 to 100 percent of the hydrocarbon constituents present
in coalbed gas, although it is common for the mixture to contain
a number of different hydrocarbon gases, plus minor amounts of
nitrogen and carbon dioxide.
In the early Twentieth century, "shale gas" was
commonly produced in the midcontinent oil and gas fields. The
common source of this gas was later proven to be the coalbeds,
which are prevalent in the region. Coalbed methane reservoirs
of the midcontinent are high, volatile bituminous A, B, and C
coals. Gas can be produced from coals of nearly every rank; however,
some of the less attractive coals (e.g., lignite) may require
substantial bed thickness to develop adequate reserves. The industry
continues to grow, and is active in nearly every sedimentary
basin in the United States, primarily the San Juan, Black Warrior,
and Raton basins.
Coal, a very complex mixture of organic and inorganic compounds,
differs from other sedimentary reservoirs as the gas is adsorbed
within the matrix of the rock rather than compressed in pore
spaces. A typical one-foot thickness of coal six hundred feet
deep is capable of containing as much gas as a typical sandstone
reservoir five thousand feet deep. Another unique characteristic
of coalbed production is its producing behavior. In most cases,
initial production of gas is quite low while water production
may be high. As the water is withdrawn, and the bottom-hole pressure
decreases in the reservoir near the wellbore, gas production
gradually increases. During the first few producing months the
water-producing rate will continue to decrease accompanied by
an increase in the gas-producing rate, until a pseudo-steady
state occurs for both phases.
Due to its unique characteristics, coalbed evaluation requires
methods not prevalent in other oil and gas producing operations.
Coal rank is determined by measuring the light reflected from
the surface of coal samples - vitrinite reflectance. Drill cuttings
or core samples are analyzed for gas-in-place content by means
of a canister test. Proximate analysis of coal, the same method
utilized by the mining industry to determine coal quality, is
a usable tool to estimate gas absorbing potential of various
coals. The plot of a laboratory measurement of a coals gas-absorbing
capability, the isotherm, is useful in determining the gas-content
of coals, critical pressures, and estimating residual gas at
The gas storage capacity of a coal is a complex function of
reservoir temperature and pressure, composition, micropore structure
and molecular properties of the adsorbed gas. In addition the
geology of the coal deposit and the surrounding rocks can affect
gas content and deliverability (e.g., cleat structure). Core
samples are being collected from continuous cores using the KGS's
coring rig and wells of opportunity. Samples are analyzed to
determine the gas-in-place value, gas composition, and gas storage
capacity. Selected samples of key coals are characterized as
to cleat structure and by proximate analysis to determine ash
content, moisture, volatile matter and fixed-carbon content.
Studies are being carried out to evaluate the regional geology
and CBM production potential of coal deposits throughout eastern
Kansas. The stratigraphic architecture of the coal-bearing Middle
Pennsylvanian strata is being studied by mapping CBM fields and
characterizing production, constructing correlation sections,
structure, isopach and derivative maps, and digital datasets.
Completions of coalbed wells require unconventional methods
in most cases. Chemical treatments, cementing, and hydraulic
fracturing require a knowledge of the coal, otherwise substantial
reservoir damage may occur. Casing installation should be designed
to prevent damage and allow adequate space for phase separation
and pumping equipment.
Coalbed gas reserves, not unlike conventional reservoirs,
may be estimated by analogy, volumetric methods, material balance
calculations, or decline curve extrapolation.
The end products of the KGS effort will include a comprehensive
regional study and digital database of the distribution and quality
for the significant coals in the Cherokee and Forest City basins.
Limited data is currently available but is increasing rapidly.
As data is synthesized it will be made easily accessible through
the Internet and KGS Website.
Please send me ____
copies of "Fundamentals of Coalbed Methane Production".
I have enclosed $20.00 for each copy.
State: ______ Country: _________________
Postal Code: _________ Phone: ________________________
Mail: order form and check or money order payable to "The
University of Kansas" to:
Tertiary Oil Recovery Project, 1530 W. 15th St., 4008 Learned
Hall, University of Kansas, Lawrence, Kansas 66045-7609
One of the many coal samples obtained by KGS coring rig in
southeast Kansas. Core sample is placed in a desorption canister
and maintained within a controlled temperature environment. The
quantity and quality of desorbed gas is measured to determine
the gas-in-place value, gas composition, and gas storage capacity.