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Geology
Geological Sequestration of Carbon Dioxide in
Oil and Gas Reservoirs on the Texas Gulf Coast
a report by
Jean-Philippe Nicot
Geological Engineer, Texas Bureau of Economic Geology
Carbon capture and storage, a subset of which involves injecting To put these numbers into perspective, in the same most populous
carbon dioxide (CO
2
) into the subsurface in a process called section of Texas, stationary CO
2
emissions are ~333 million metric
geological sequestration (GS), has received renewed interest lately. tons per year, >70% of which comes from electricity generation.
The decision by the Obama administration to handle climate change This number is only one order of magnitude larger than the current
and the request for legislation to cap CO
2
emissions follows an ever- rate of injection of CO
2
in the Permian Basin (West Texas and south-
increasing body of work performed by scientists and engineers all east New Mexico), at 30–35 million tons per year, maybe half of
around the world, including in the US. The US Department of Energy which is recycled. A simplistic computation assuming the density
(DOE) has large programmes in place involving billions of dollars to of supercritical CO
2
to be 700kg/m
3
yields an equivalent volume of
address this important issue. In Texas, large independents such as ~3Bbbl/year of CO
2
emissions. Again, for the sake of a simple
Kinder-Morgan and Denbury Resources Inc. have been active comparison, let us compute the theoretical volume made available in
partners with scientific institutions, allowing researchers access to the subsurface by the cumulative production of hydrocarbons. Total
data and sites where CO
2
is currently injected. In addition, all majors cumulative production in RRC districts 1–6 is 12.5Bbbl of oil and
have shown a strong interest in supporting the US GS research ~30 trillion cubic feet (Tcf) of gas (equivalent volume-wise to 26Bbbl,
community. It is safe to say that West Texas is the world centre of assuming an average gas density of 140kg/m
3
). We now assume that
excellence when it comes to CO
2
injection. Consequently, Texas has we will inject the CO
2
back into the volume liberated by produced
the skilled workers and the technology required to become a major hydrocarbons that would have stayed open, notwithstanding all
player in this nascent industry. technical constraints (an optimistic view and an assumption unlikely
to be realised). Oil- and gas-depleted reservoirs could absorb
The oil and gas industry holds considerable experience and ~4 billion tons of CO
2
, which is equivalent to ~13 years of CO
2
knowledge in all of the steps (capture, compression, transport and emissions, not including CO
2
that can be stored in place of oil to be
injection) needed to process large amounts of CO
2
, and has proved potentially recovered through tertiary processes.
that it can do these things safely. To date, because most CO
2
injected in West Texas (>1 billion barrels [Bbbl] recovered through Part of the explanation as to why there is so much more space in
enhanced oil recovery [EOR]) comes from natural CO
2
accumulations saline aquifers than in hydrocarbon traps is that CO
2
has two
in other western states, it is not making a dent in the mounting CO
2
additional trapping mechanisms of interest:
atmospheric concentrations (which has never been its purpose). The
Texas Gulf Coast, in contrast, despite the presence of many •CO
2
dissolves in water, and the surrounding CO
2
-free water is
reservoirs amenable to CO
2
flooding, has never seen such a level of lighter than the CO
2
-rich water, which will tend to sink; and
activity. The strength of the Texas coast is the fortuitous spatial •CO
2
can be immobilised progressively by residual saturation
match between CO
2
emission sources (coal-fired power plants, trapping as it migrates upwards.
cement plants and petrochemical facilities) and a large storage
capacity, including oil and gas reservoirs. The latest US DOE study on Note that both mechanisms are more permanent than storage in
GS capacity
1
comments on this spatial adequacy, pointing to an closed structures, which is typical for hydrocarbons, because, in the
impressive >500 billion metric tons of CO
2
capacity in saline aquifers latter case, buoyancy remains a strong driving force ready to take
in Texas east of the major metropolitan areas of Dallas-Fort Worth advantage of any potential leakage pathway. However, the interest
and San Antonio. This area covers, approximately, Railroad and strength of CO
2
storage in oil and gas reservoirs do not reside
Commission of Texas (RRC) – the Texas state agency regulating the in their ultimate capacity, but rather in their ability to jump-start a
oil and gas industry – districts 1–6, and contains the city of Houston. sequestration industry in Texas. Although the bulk of the capacity is
in saline reservoirs, there is no economic incentive to use this
available space. The concept of stacked storage can then be
Jean-Philippe Nicot is a Geological Engineer with the
Texas Bureau of Economic Geology. His research
developed, in which the infrastructure needed for large-volume CO
2
interests include understanding the risks associated
disposal is initially built for the purpose of CO
2
–EOR. The same
with geological storage of CO
2
and its potential
infrastructure is subsequently used to transport and store additional
impact on water resources, and developing ways to
manage the transition to a carbon-constrained world. CO
2
in under- or overlying formations.
Dr Nicot has worked on environmental issues such as
contaminated site clean-up and nuclear waste
disposal. He holds a PhD in civil engineering from the
Several attempts have been made to estimate the amount of oil
University of Texas at Austin. recoverable by CO
2
–EOR in the Texas Gulf Coast. At least 13.5Bbbl of
E: jp.nicot@beg.utexas.edu
oil is left as residual saturation, not all of it recoverable (play-averaged
recovery efficiencies in major Texas oil reservoirs range from 28 to
40
© TOUCH BRIEFINGS 2009
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