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Die Speicherung von Kohlendioxid in geologischen Formationen wird derzeit als ein moglicher Beitrag zur Reduktion von Treibhausgaskonzentrationen in der Atmosphare diskutiert und untersucht. Ein wichtiges Werkzeug begleitend zu experimentellen Untersuchungsmethoden ist die numerische Simulation. Hier wird ein Einblick in die physikalischen bzw. thermodynamischen Vorgange im Untergrund wahrend und nach einer Injektion von Kohlendioxid gegeben sowie deren modellkonzeptionelle Beschreibung durch nichtisotherme Mehrphasensysteme dargestellt. Die elementaren Schritte der physikalisch/mathematischen Modellbildung und numerischen Losung der daraus entstehenden Gleichungssysteme werden erklart. Anhand von Simulationsbeispielen werden dominierende Prozesse wahrend und nach einer Injektion diskutiert.

Carbon dioxide ( CO 2 ) injection into a storage formation is accompanied by non-isothermal effects. These are caused by a CO 2 injection temperature that does not correspond to the formation temperature, cooling of the carbon dioxide due to expansion (Joule–Thomson cooling) and heat of dissolution of CO 2 in brine. During flow in the subsurface, the carbon dioxide transports energy (advective heat transport) and undergoes an equilibrating process between temperature differences (heat conduction). These non-isothermal processes can be used for the purpose of monitoring the CO 2 plume propagation in the subsurface. Temperature sensors at monitoring wells at a certain distance from the injection well can detect temperature changes and give information about the CO 2 flow in the storage site. In this study, a numerical multi-phase simulation program is used to investigate the non-isothermal effects during CO 2 injection into a storage formation. The feasibility of using temperature measurements for the observation of the carbon dioxide plume in the reservoir is addressed. Various thermal processes and their dependency on the geological characterisation of the reservoir are discussed in detail.

This study examines the suitability of thermal methods, especially DTS (Distributed Temperature Sensing) cables (in the annulus or behind casing) to monitor the fate of injected CO2 for emissions reduction purposes. The static temperature signal of CO2 stored in pores of sandstone and claystone examples is calculated as a function of porosity, CO2 saturation, and CO2-filled reservoir thickness. The dynamic temperature signal associated with the movement of CO2 in the well and the porous rock is discussed and results of numerical simulations are presented. The detectability of these temperature signals is assessed and found to be useful in detecting leakage over short time intervals and saturation changes in the storage reservoir over the longer term.

Publisher Summary Different kinds of subsurface reservoirs have been proposed for geologic disposal of greenhouse gases, including saline aquifers (brine formations), depleted or depleting oil and gas reservoirs, and coalbeds. Injection of greenhouse gases into such formations will give rise to complex coupled processes of fluid flow, mechanical and chemical changes, and heat transfer. Mathematical models and numerical simulation tools will play an important role in evaluating the feasibility of geologic disposal of CO 2 , and in designing and monitoring CO 2 disposal operations. The models must accurately represent the major physical and chemical processes induced by injection of CO 2 into potential disposal reservoirs, such as miscible and immiscible displacement, partitioning of CO 2 among different fluid phases, chemical reactions, thermal effects, and geomechanical changes from increased pore pressures. It is essential to test and evaluate numerical simulation codes to establish their ability to model these processes in a realistic and quantitative fashion. The code inter-comparison study reported in this chapter is a first step in this direction.

We discuss the influence of heterogeneities on multiphase flow, focussing on the numerical handling of critical effects at the interfaces between two domains with different soil properties and capillary pressures. An example is given, where we show the different results obtained with different numerical methods applied to a 1D heterogeneous two-phase system.