Ernie Perkins

Aquifer disposal of CO2: Hydrodynamic and mineral trapping

A general approach to evaluating sedimentary basins for CO2 disposal is presented in this paper. The approach is exemplified for the case of the Alberta Basin in western Canada where a wealth of geological and hydrogeological data from more than 150,000 wells drilled by the oil industry allows for a proper estimate of the basin potential for long-term storage of CO2 captured from fossil-fuelled power plants. Geochemical and hydrogeological analyses of CO2 interaction with the aquifer water and rocks, and of CO2 transport in miscible and immiscible phase by the natural flow of aquifer water indicate that, besides stratigraphic trapping, two additional mechanisms are available for the capture and long-term retention of CO2 in the subsurface. One mechanism is mineral trapping through precipitation of carbonate minerals when CO2 is injected into basic siliciclastic aquifers. The other mechanism is hydrodynamic trapping when the residence or travel time of CO2 in low permeability regional aquifers is of the order of thousands to a million years.

Aquifer disposal of CO2-rich greenhouse gases: Extension of the time scale of experiment for CO2-sequestering reactions by geochemical modelling

SummaryIn previous work,Gunter et al. (1993), suggested water-rock reactions in deep aquifers in sedimentary basins could sequester injected-CO2-waste from industry, thereby reducing greenhouse gas emissions. Experiments, carried out at 105°C and 90 bars CO2 pressure, to test the validity of this mineral-trapping of CO2 were unsuccessful due to sluggish kinetics of reaction. The most significant change recorded by the reaction products from these experiments was a large increase in alkalinity, which was attributed to very small amounts of water-mineral reaction. A computer model, PATHARC.94, was used to interpret this change in alkalinity and to predict the path and time necessary to reach equilibrium. Substantial trapping of CO2 by formation of siderite, calcite and aqueous bicarbonate ions was predicted to occur in 6 to 40 years.Potential errors as high as two orders of magnitude were estimated based on a thorough examination of the kinetic data used in the modelling. In order to achieve reasonable time estimates, “reactive” surface areas were approximated by 100 micron spherical grains in the computer model. This represents a smaller cumulative surface area than actually present in the experiment. When these results are extrapolated to the field, where the aquifers are at lower temperatures,Perkins andGunter (1995a), concluded that CO2-trapping reactions are expected to take 100s of years to complete. This is sufficient time for the trapping to occur as the residence time of a packet of fluid in a deep low-permeability aquifer in a sedimentary basin is measured in 10,000s to 100,000s of years.ZusammenfassungIn früheren Arbeiten habenGunter et al. (1993) Wasser-Gesteinsreaktionen in tiefen Aquiferen in Sedimentbecken vorgeschlagen, die injiziertes CO2 aus industriellen Abgasen aufnehmen, und damit die Treibhausgasemissionen reduzieren könnten. Experimente wurden bei 105°C und 90 bar CO2-Druck durchgeführt, um die Anwendbarkeit dieser mineralischen Fallen für CO2 zu testen; wegen der langsamen Reaktions-Kinetik waren diese nicht erfolgreich. Die markanteste Änderung, die diese Experimente in den Reaktionsprodukten hervorriefen, war eine beträchtliche Zunahme der Alkalinität, die auf geringfügige Wasser-Mineralreaktionen zurückgehen dürfte. Ein Computermodell, PATHARC 94, wurde benützt, um diese Änderungen der Alkalinität zu interpretieren und die erforderlichen Zeiten und Pfade vorherzusagen, die notwendig sind, um Gleichgewicht zu erreichen. Signifikanter Einbau von CO2 durch Bildung von Siderit, Calcit und Bikarbonat-tonen sollte dementsprechend in 6 bis 40 Jahren stattfinden.Mögliche Fehler, die bis in zwei Größenordnungen gehen können, wurden aufgrund einer sorgfältigen Überprüfung der kinetischen Daten, die hier benützt wurden, ermittelt. Um sinnvolle Zeitmaßstäbe zu erreichen, wurden im Computermodell “reaktive” Ober flächen durch 100 Mikron große kugelförmige Körner repräsentiert. Dies stellt eine kleinere Gesamtoberfläche dar, als die, die tatsächlich im Experiment vorhanden ist. Wenn diese Ergebnisse ins Gelände extrapoliert werden, wo die Aquifere niedrigere Temperaturen aufweisen, kommenPerkins undGunter (1995a) zu dem Schluß, daß ein vollständiger Einbau von CO2 hunderte von Jahre benötigen würde. Diese Zeiträume sind ausreichend, da die Verweildauer einer Fluid-Menge in einem tief gelegenen Aquifer mit niedriger Permeabilität in einem sedimentären Becken in Größenordnungen von 10.000 bis 100.000 von Jahren gemessen wird.

Aquifer disposal of acid gases: modelling of water–rock reactions for trapping of acid wastes

Abstract The pore space of deep saline aquifers in the Alberta (sedimentary) Basin offers a significant volume for waste storage by “hydrodynamic trapping”. Furthermore, given the slow regional fluid flow in these deep saline aquifers, ample time exists for waste-water/rock chemical reactions to take place. A geochemical computer model (PATHARC) was used to compute the interaction of industrial waste streams comprising CO 2 , H 2 SO 4 and H 2 S with the minerals in typical carbonate and sandstone aquifers from the Alberta Basin. The results support the idea that these acids can be neutralized by such reactions and that new mineral products are formed, such as calcite, siderite, anhydrite/gypsum and pyrrhotite, thereby trapping the CO 3 , SO 4 and S ions that are formed when the acid gases dissolve in the formation water. Siliciclastic aquifers appear to be a better host for “mineral trapping” than carbonate aquifers, especially with regard to CO 2 . Carbonate aquifers may be more prone to leakage due to high CO 2 pressures generated by reaction with H 2 SO 4 and H 2 S. Even though permeability decreases are expected due to this “mineral trapping”, they can be partially controlled so that plugging of the aquifer does not occur.

Long term predictions of CO2 storage by mineral and solubility trapping in the Weyburn Midale reservoir

Publisher Summary The chapter uses geochemical modeling to interpret the potential of long term storage of carbon dioxide in the Weyburn Midale reservoir, and to interpret if geochemically reactive zones exist around the reservoir. Although there are differences between the various flow units within the reservoir, the net long-term reactions are similar in all of them. Up to approximately 10 years, the precipitation of calcite and kaolinite, and the dissolution of anhydrite and various silicate minerals are predicted. In close cooperation with the International Energy Agency, an international multi-disciplinary research initiative to study the short and long-term potential of geological storage of CO 2 in a carbonate reservoir has been established. Water-rock reactions are critical to the short- and long-term storage of injected CO 2 and the quantification of CO 2 storage via such reactions is an important piece of the research puzzle.

Recovery of trace metals in formation waters using acid gases from natural gas

Abstract The maximum contents of Pb (360 mg l−1), Zn (360 mg l−1) and Ag (7.9 mg l−1) in formation waters from the Alberta basin were high enough to suggest that it would be of interest to test the concept of recovering these metals by passing natural gas through the water, thereby precipitating the metal sulphides as the result of contact with hydrogen sulphide. The idea was to see if these metals could be recovered from formation water co-produced with crude oil prior to disposal of the water in deep formations, with the possibility of the sale of the metals partially offsetting the cost of disposal. It was proposed to use natural gas with a relatively small amount of hydrogen sulphide (insufficient for sulphur recovery) that must be removed by flaring before the gas is utilized. Accordingly, a database of 694 formation waters with major, minor and trace components was searched for appropriate analyses for detailed study. Of the nine analyses selected the majority were from Devonian and Granite Wash aquifers in the Peace River Arch area of northern Alberta, Canada. Modelling with PATH.ARC showed that there is a consistent set and order of precipitation reactions, in spite of the differences among the formation waters. As would be expected intuitively, acid gas addition makes the formation water more acidic, and metallic sulphide minerals are precipitated. Depending on the initial composition, the end minerals are any of galena, sphalerite, acanthite, covellite and pyrite. These are the minerals that must be beneficiated to recover the metals. A preliminary evaluation of the dollar value of the recovered metals shows that although the absolute values are low, there may be an advantage to recovering the metals if the waters are already being handled at the surface.

- Geochemical monitoring of gas-water-rock interaction at the iea Weyburn CO 2 Monitoring and Storage Project, Saskatchewan, Canada

Publisher Summary The Weyburn Oil Field is the site of EnCanas C02-injection enhanced oil recovery (EOR) project in a carbonate reservoir in southern Saskatchewan. An IEA-sponsored program was initiated to evaluate the potential for geological storage of greenhouse gases. Geochemical monitoring and modeling plays an important role in assessing gas-fluid-rock interactions. The geochemical dataset is the primary input for quantifying the short- and long-term (years to thousands of years) CO2 storage potential in the basinal brine, non-recoverable oil, and in newly precipitated minerals. Three geochemical processes have been found occurring in the area of the reservoir as a result of CO2 injection: (1) rapid CO2 dissolution in the brine and oil; (2) the CO2 “sweep” previously assessing the inaccessible portions of the reservoir; and (3) carbonate mineral dissolution due to acidification of the basinal brine. Equilibrium relations among gases, brines, and liquid hydrocarbons in the Weyburn field demonstrated a close correlation among dissolved CO2, free gaseous CO2, and the amount of injected CO2.

Mineralogical characterization of the Weyburn reservoir, Saskatchewan, Canada: Are mineral reactions driving injected CO2 storage?

Publisher Summary The Weyburn Oil Field is the site of EnCanas large C02-injecfion enhanced oil recovery project in southern Saskatchewan, Canada. The Weyburn field is one of a number of large oilfields that lie along the Mississippian subcrop belt on the northern part of the Williston Basin. In close cooperation with the International Energy Agency, an international multi-disciplinary research initiative to study the short and long-term potential of geological storage of CO2 in a carbonate reservoir has been established. Although the Weyburn Midale reservoir is dominantly calcitic and dolomitic, significant amounts of potentially reactive silicate minerals are present to assist in CO2 storage have grouped CO2 trapping into three types. Type 1 capture is defined as occurring when a mineral is precipitated incorporating the anion formed by the dissolved gas. Type 2 capture is defined as occurring when an acid gas is neutralized in solution forming a nonvolatile soluble salt and subsequently leading to brine formation. Type 3 capture is characterized by CO2 trapping in both solid and aqueous phases. The detailed mineralogy of the Weyburn reservoir, with particular attention paid to EnCanas flow unit nomenclature, is described. Mineral reaction modelers, assessing the long-term fate of injected anthropogenic CO2, may use the mineral modes of flow units as input variables.