Crossing the Disciplines: Similarities and Differences of Modelling of CO2 Sequestation and Modelling of Oil and Gas Migration

Christian Hermanrud, Silje Berg, Ola Eiken, Hege M. Nordgård Bolås, Gunn Mari Grimsmo Teige, and Peter Zweigel
Statoil, Norway

Underground storage of CO₂ has been predicted a substantial expansion in the years to come. Such storage requires analyses of. sealing potential of the depositories, gas flow in porous media, seismic monitoring of possible gas leakage through caprocks, and fluid / rock interactions. Knowledge of these subjects resides in the petroleum community, but the applications to CO₂ storage demands new approaches to several of the involved subjects. Modelling of the flow of CO₂ storage can include both pre-injection investigations and modelling of the displacement of CO₂ with water as injection proceeds. While experiences from both reservoir modelling and integrated basin modelling will be helpful in such modelling, neither is equipped to deal with factors such as (a) modelling of seismic consequences of leakage in the overburden, (b) pH changes and associated mineral dissolution due to CO2 injection, (c) subsurface permeability changes and soft sediment deformation as a result of CO₂ injection, (d) adsorption of CO₂ in coals and liberation of adsorbed methane as a consequence. The time scale of interest to CO₂ storage is in the order of thousands of years, which places it between the time scale of reservoir modelling (tens of years) and basin modelling (million of years). This difference implies that rocks that seal in a production timescale, but leak in geologic time, need special attention. This is especially a challenge when it comes to investigations of vertical leakage, where our present process understanding is quantitatively incomplete. In addition, the knowledge of the reservoir properties of CO₂ storage sites varies substantially, depending on whether CO₂ is injected into a hydrocarbon reservoir or not. Risk analyses also differs between hydrocarbon exploration, production and CO₂ storage studies. Risk is always involved in petroleum related investigations of hydrocarbon movement and trapping. A certain risk is acceptable in such studies (including the risk of drilling dry wells), and the risk is communicated among professionals. Risking of CO₂ storage is different in that it is communicated not only to the CO₂ storage decision makers, but also to legislators and the general public, who at times may require technically unrealistic accuracy of the risk assessments.

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands