Evaluation of the Potential for CO2 Sequestration in Deep Formations Beneath Ohio
Beverly Saylor (Department of Geological Sciences,
Case Western Reserve University, Cleveland, Ohio, USA)
Ohio Geological Society meeting
12 November 2001
We're iterested in taking CO2 from power plants and injecting it into deep formations and see it, hopefully, staying there - the goal is to help prevent emission of a key greenhouse gas.
Ohio has a good potential for CO2 sequestration, especially in the coal producing areas of eastern Ohio and in deep, extensive oil aquifers that are not producing anymore. CO2 injection will also help in enhanced oil recovery from producing wells.
Enhanced oil recovery (EOR) by miscible CO2 flood, using the WAG approach (water after gas) - repeated gas, then water, then gas, then water injection method. CO2 maintains pressure in the reservoir and decreases the viscosity of the oil, and geometric traps will store the CO2.
Existing EOR using CO2 has as a goal of getting as much CO2 back out of the system as possible, since the CO2 has to be paid for. The approach discussed here is a bit different.
Coal-bed methane recovery (CBMR) by CO2 flood is another potential operation. The CO2 will maintain pressure, desorb CH4, and adsorption to coal stores the CO2.
Need pure-as-possible CO2 from stacks to do EOR (N2 in there, for example, has less effective results). CBMR doesn’t require pure CO2.
A third option for CO2 sequestration is injecting CO2 into deep saline aquifers. Saylor hasn’t ruled out this approach, but is moving away from this idea. Examples in Ohio include the Mt. Simon Sandstone [Cambrian] and Rose Run Sandstone [Cambrian] (where it isn’t an oil/gas reservoir). The mechanisms for CO2 sequestration in this situation are hydrodynamic trapping (versus geometric trapping above), and mineral trapping of CO2 as carbonate. The formation waters in these reservoirs are moving downdip (we hope) toward Pennsylvania. The CO2 dissolves into the saline waters or mixes with the saline waters or mineralizes out as silicate minerals dissolve and carbonate minerals crystallize. Permanent mineral trapping of CO2 - would this work, though and how long would this take after injection? Deep saline aquifers have high storage volumes, but this option is way down the line.
Need to look at the EOR/CBMR approaches first to get a feel for how CO2 sequestration works there. Looking at this problem at the basin scale and at the microscale.
Porous flow - true paths of particles are crooked, and often fluid gets trapped at corners or at blind ends - studying how this relates to mineral trapping of CO2.
Looking at the distribution of Ohio power plants and oil/gas production areas - several plants are in eastern Ohio, but several are in west-central and southwestern Ohio, away from o/g reservoir areas.
CO2 floods in EOR has been going on for ~20 years (~1978 start with gusto in the Permian Basin, for example). Ohio has a good potential for EOR and CO2 storage. Also potential (??) for enhanced gas recovery.
Evaluating the Rose Run Sandstone of Ohio for this idea - EOR is possible and so is aquifer storage for CO2.
Significance of mineral-brine-CO2 reactions - we’re interested in the integrity of the seal (especially considering that CO2 is acidic) and the permeability near the injection site (will we clog up the injection site with mineral formation? This is not much of a problem yet with carbonate reservoirs, but need more research on the problems of this in sandstone reservoirs. Get precipitation of clays and calcite along pore throats), the extent of mineral trapping, and the capacity & duration of storage.
Why study the Rose Run? It is the most shallow of the deep aquifers in Ohio. Also looking at the Mt. Simon as a potential aquifer. The Kerbel Sandstone [Cambrian] might work. The Rose Run is the shallowest, but it is not the simplest. Studying the heterogeneity of the Rose Run will help in understanding the potential of CO2 sequestration in Ohio.
The Rose Run consists of carbonate platform sediments with sand coming in from the craton from the west that interfinger with the carbonates. The Rose Run is the equivalent of the upper sandy member of the Gatesburg Formation [Cambrian] of Pennsylvania.
Looked at exposures of the Rose Run (= upper sandy member of the Gatesburg) at Tyrone, Pennsylvania, which is near State College/Penn State. See a succession of lithofacies: planar-laminated sandstones, trough-cross-laminated sandstones, ooid grainstones, burrowed ooid packstones and wackestones, microbial bioherms, laminites, and dolosiltstones interbedded with sandstone.
Planar-laminated sandstone facies - commonly with sharp erosive bases with rippled tops, rip-up clasts, tidal zone deposition, almost channel-like.
Trough-cross-laminated sandstone facies
Ooid grainstone and burrowed ooid packstone facies - the burrowed parts are well mottled. These have faint planar laminations and some trough x-stratification. The ooid grainstones are often atop sandstones - often have mixed transition between the two units - the sand grains and the ooids look alike at outcrop and are easily confused.
Microbial bioherm facies - a tremendous variety here, ranging from stromatolites to thrombolites (up to 1 meter tall and 4 meters across), surrounded by ooid grainstone facies. Get everything in-between stromatolites and thrombolites also. The microbial bioherm facies is closely associated with the ooid grainstone facies. The stromatolites here aren’t analogous to Shark Bay stromatolites, but rather are comparable with subtidal stromatolites seen in the Bahamas (not Shark Bay type).
Laminite facies - mm-laminated, slightly wavy and crinkly, with desiccation cracks; supratidal mudcracked microbial mats (see Andros Island analogues).
Ooid packstone & wackestone facies
Sandy dolosiltite facies - common facies in cores, but more islated in the Pennsylvania outcrops. Has burrows - crinkly burrows with sand fillings.
Subtidal cycles - these facies do form cycles - repetitively stacked successions: light gray sandstone (with sharp erosive base and rip-up calsts & carbonate mud mixed in) to darker gray laminated grainstone to burrowed-mottled packstone & repeat.
Sands could be interpreted as channels - but Saylor doesn’t like this idea.
What’s causing the sandstone/carbonate intercalations is the key to understanding these cycles.
The sandstone-carbonate subtidal cycle may be due to sea level change.
Looking at the Tyrone outcrops, looking for Enterline’s 1991 thesis core from Ashtabula County and a Coshocton County core, and hopefully as many other cores as possible.
The lower parts of the Tyrone outcrops have repeated subtidal cycles and the upper parts of the Tyrone outcrops have tidal flat cycles (laminites with interbedded sandstones and burrowed recrystallized wackestone - finer-grained seds. that lack ooids). These Tyrone outcrops cycles are parasequences (shallow-up successions in general, apparently). There's hummocky cross-stratification present in the dolostiltite above the lower Gatesburg sandy member.
Enterline’s 1991 Ashtabula County core has more tidal flat facies represented. The examined Coshocton County core is further toward the land - more sand and fewer carbonates - silt even in where you have carbonates - backing up from the intertidal areas.
The Bahamas are not a good analogue to this Rose Run system (the Bahamas lack siliciclastics). Florida is better, but it still has problems being a good analogue.
The Rose Run has mixed lithologies at the meter-scale and at the thin-section scale. It has silicified ooids and sand. Dissolution clears out the carbonate portions of ooids (have quartz nuclei, often) and have quartz precipitated in its place. Not a lot of feldspar - what little there is has been dissolved away, accounting for some of the porosity in the Rose Run.
Did a correlation of the five Rose Run sandstone layers to see the geometries of these sandstone/carbonate intervals.
1) Carbonate aquifer:
CO2 + H2O + CaCO3 [calcite] --> Ca2+ + 2HCO3-
2) Siliciclastic aquifer, alkali phases
2KAlSi3O8 [K-feldspar] + CO2 + H2O -->
2K+ + HCO3- + Al2Si2O5(OH)4 [illite] + 4SiO2 [quartz]
3) Siliciclastic aquifer, alkali Earth phases
CaAl2Si3O8 [plagioclase feldspar] + CO2 + 2H2O -->
CaCO3 [calcite] + Al2Si2O5(OH)4 [illite]
It will take time to dissolve feldspars (too long?) & precipitate out clay.
There's also glauconitic sandstone in the Rose Run - need to see how that reacts...
Lab experiments are testing the speed of these reactions. Then, will do modeling of these reactions.
Particle image velocimetry - using see-through rock models, seeing flow path geometries. This model also describes Leisgang banding. Using a laser to see what’s happening at the pore scale. Laser-based imaging needs something that reflects light - have optically transparent particles as the framework but need reflective micron-scale particles as the flow medium for laser light reflection. Can track individual particles - can determine velocities, flow paths, etc.
Summary - Potential for aquifer and reservoir sequestration is high in Ohio (it’s as good here as its going to be anywhere). Good potential for EOR. Acid waters and dissolution are expected. Mineral trapping as calcite is important. Knowing speed of reactions is critical.
See Russell Kansas Project - using CO2 in EOR as part of an ethanol production system (from Carr).
The Rose Run Sandstone looks like, in general, a progradational succession, but with something else also going on, maybe.