WATER RESOURCES
ASSOCIATED
WITH
UNCONVENTIONAL O&G DEVELOPMENT
Energy production represented by oil and gas extraction
has been one of the major industries in Texas for more
than 100 years. The fields that were discovered during
this time are nearing their economic limit. One reason
that O&G operators are interested in desalination of
produced water is that it has the chance of reducing
operating costs of their wells, and extending their
lifetimes. Within the last 10 years however,
unconventional reservoirs are being brought on
production as new technology makes their development
economical. Most of the attention to unconventional
resources has been focused on coal bed natural Gas (CBNG).
Figure 12 shows CBNG resources in Texas and nationwide.
These resources have an estimated 750 trillion cubic ft
of natural gas.
The increase in
importance of CBNG and other unconventional resources is
the result of a combination of factors, tax breaks for
exploration, research funding that triggered new
technology in imaging, horizontal wells, and hydraulic
fracturing and high gas prices. As the figure shows,
much of the energy play is in environmentally sensitive
areas, in the West public lands, and in the East,
populated areas that have not experienced oil and
gas“booms”.
Figure
12. Unconventional Shale Gas Resources in the U.S.
Despite the issues related to the impact of drilling in
environmentally sensitive areas, and despite the needs
for technology advances, most industry specialists
believe that this source of energy for the U.S. is
destined to become more and more important. Figure 13
shows a chart resulting from a study by the Petroleum
Technology Council )PTTC) [46]. The contribution of
unconventional resources increases steadily over the
next 50 years until it represents more than 50% of the
U.S, natural gas needs.
Figure 13 shows gas
production forecasts for the lower 48 states and
Canadian Fields for the next 20 years. Source PTTC [49]
In
Texas, the most activity is in the Barnett Shale play in
North Central part of the state. In the past three
years, the drilling boom in the Barnett Shale has become
the most active area in the U.S. The field, the largest
active gas field in Texas, now produces more than 220
Bcf of natural gas per year.
Drilling activity isn’t limited to Texas however.
Unconventional energy resources in Oklahoma include
Hunton de-watering and coal bed methane (CBNG activity
in the Arkoma and Cherokee basins [7,8] CBNG active in
Oklahoma's Arkoma Basin produced about 70 Bcf of gas
cumulatively through mid-2003. About two-thirds of this
production is from vertical wells, but horizontal
production is rapidly overtaking that from vertical.
Cherokee Basin CBNG cumulative production is about 45
Bcf, all from vertical wells. CBNG well in southeast
Kansas are now producing about 10 Bcf per year, and
activity is strong. Arkansas CBNG production is just now
begun to increase.
Water Resources Used in
Energy Production
The connection between unconventional energy resources
and water resources is typified by the photograph in
Figure 14. It shows a well fracturing operation in the
Barnett Shale using fresh water from the municipality of
Cleburne, Johnson County Texas. Cleburne sells water to
operators at retail rates to stimulate Barnett Shale
wells. A horizontal well fracturing operation uses on
average 5 million gallons of water to create vertical
fractures that intersect natural fissures in the shale.
Flow back of the water, now containing mineral salts
from the underground formation, occurs over a period of
several days to months.
Figure
14 is a photograph of a fracturing operation in the
Barnett Shale.
Flow back water must be captured in lined pits and
transported to off site disposal. Salinity
characteristics of this brine vary greatly, depending on
the amount of flow back water, the zone that has been
discharging the water, and the formation water content
as a component of the fracturing water. Table 10 shows
typical analytical data from water transport trucks
carrying brine to off-site disposal. Total dissolved
salts are in excess of 100,000 ppm. Total suspended
solids (TSS) are likewise quite high averaging almost
200 ppm for transport samples and more than 15,000 for
the pit sample.
The issue is that all of the fresh water must be
transported in to the site, then all of the flow back
brine stored, re-loaded in transports and trucked to
disposal wells that be dozens of miles away. The brine
water is then injected and lost permanently from the
environmental natural water.
Table 10. Composition of
Typical Flow Back Water from Barnett Shale [47]
The Social Cost of Energy
Production
The
issue of supplying adequate water resources for
communities intersects with the need for water resources
for energy production for those communities. Efforts by
Texas A&M and others to reduce the use of water in
energy production and to make fresh water available for
those communities is part of the process of sustainable
natural resource development.
Texas,
in the 21st century is becoming a different society than
most adults recall growing up. In almost every county in
Texas, the population is shrinking. The urban centers
and the counties near the urban areas are absorbing
practically 100% of the state’s population growth. On
the other hand, almost 100% of the population would
rather live in a small community. It is only because
there are few jobs and inadequate social infrastructure;
most end up in the cities.
When
economic booms come to local communities, many times its
leaders are unable to cope with the change. The role of
state and federal government in local communities is
diminishing as funds for economic development are
stretched. It is becoming the responsibility of the
communities themselves to take lead in their own
survival and development. Unconventional energy
development brings both good and bad changes to these
cities. The ability to recover water resources from
energy development helps to accommodate the changes it
brings.
There is new technology for developing new sources of
fresh water for the community. Two examples are the
desalination of brackish water from underground aquifers
to make it potable and the treatment and desalination of
oil field produced water to make it usable for
livestock, agriculture and industrial uses.
Studies have shown that it is extremely important that
the user (defined as local community who might have a
use for the water) be included in the change process
that comes from adoption of this new technology. The
user’s interest in anyone’s recommended systems is very
important because these interests are the basis for the
system’s acceptance and adoption.
