Carbon capture and storage, a subset of which involves injecting carbon dioxide (CO2) into the subsurface in a process called geological sequestration (GS), has received renewed interest lately. The decision by the Obama administration to handle climate change and the request for legislation to cap CO2 emissions follows an everincreasing body of work performed by scientists and engineers all around the world, including in the US. The US Department of Energy (DOE) has large programmes in place involving billions of dollars to address this important issue. In Texas, large independents such as Kinder-Morgan and Denbury Resources Inc. have been active partners with scientific institutions, allowing researchers access to data and sites where CO2 is currently injected. In addition, all majors have shown a strong interest in supporting the US GS research community. It is safe to say that West Texas is the world centre of excellence when it comes to CO2 injection. Consequently, Texas has the skilled workers and the technology required to become a major player in this nascent industry.
The oil and gas industry holds considerable experience and knowledge in all of the steps (capture, compression, transport and injection) needed to process large amounts of CO2, and has proved that it can do these things safely. To date, because most CO2 injected in West Texas (>1 billion barrels [Bbbl] recovered through enhanced oil recovery [EOR]) comes from natural CO2 accumulations in other western states, it is not making a dent in the mounting CO2 atmospheric concentrations (which has never been its purpose). The Texas Gulf Coast, in contrast, despite the presence of many reservoirs amenable to CO2 flooding, has never seen such a level of activity. The strength of the Texas coast is the fortuitous spatial match between CO2 emission sources (coal-fired power plants, cement plants and petrochemical facilities) and a large storage capacity, including oil and gas reservoirs. The latest US DOE study on GS capacity1 comments on this spatial adequacy, pointing to an impressive >500 billion metric tons of CO2 capacity in saline aquifers in Texas east of the major metropolitan areas of Dallas-Fort Worth and San Antonio. This area covers, approximately, Railroad Commission of Texas (RRC) – the Texas state agency regulating the oil and gas industry – districts 1–6, and contains the city of Houston. To put these numbers into perspective, in the same most populous section of Texas, stationary CO2 emissions are ~333 million metric tons per year, >70% of which comes from electricity generation. This number is only one order of magnitude larger than the current rate of injection of CO2 in the Permian Basin (West Texas and southeast New Mexico), at 30–35 million tons per year, maybe half of which is recycled. A simplistic computation assuming the density of supercritical CO2 to be 700kg/m3 yields an equivalent volume of ~3Bbbl/year of CO2 emissions. Again, for the sake of a simple comparison, let us compute the theoretical volume made available in the subsurface by the cumulative production of hydrocarbons. Total cumulative production in RRC districts 1–6 is 12.5Bbbl of oil and ~30 trillion cubic feet (Tcf) of gas (equivalent volume-wise to 26Bbbl, assuming an average gas density of 140kg/m3). We now assume that we will inject the CO2 back into the volume liberated by produced hydrocarbons that would have stayed open, notwithstanding all technical constraints (an optimistic view and an assumption unlikely to be realised). Oil- and gas-depleted reservoirs could absorb ~4 billion tons of CO2, which is equivalent to ~13 years of CO2 emissions, not including CO2 that can be stored in place of oil to be potentially recovered through tertiary processes.
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