Investigating Sequestration Potential of Carbonate Rocks during Tertiary Recovery from a Billion Barrel Oil Field , Weyburn , Saskatchewan : the Geoscience Framework ( IEA Weyburn CO 2 Monitoring and Storage Project )
Introduction In Western Canada the application of CO2 injection for enhanced, ‘tertiary’ oil recovery is a relatively recent addition to the arsenal available to reservoir engineers. The first successful application of CO2 as a miscible fluid in Western Canada began in 1984 at Joffre Field, a Cretaceous marine siliciclastic reservoir in southern Alberta. A significant portion of the remaining proven conventional oil reserves in Western Canada, however, reside in large mature Paleozoic carbonate fields, such as the Mississippian Weyburn Field in SE Saskatchewan (Figure 1). In combination with economically dictated tertiary recovery schemes, these large fields could provide attractive geologic sites for future sequestration of greenhouse gases. An immediate challenge to geoscientists is to assess the ability of these geologic containers to store CO2 for geologically significant lengths of time.
The Stress Regime of The Western Canadian Basin and Implications for Hydrocarbon Production
ABSTRACT In the Western Canadian Basin, overcoring measurements, hydraulic fractures, bed-slip movements and wellbore breakouts suggest a contemporary stress regime where from surface to about 350 m depth SHmax>SHmin>Sv, from about 350 m to about 2500 m depth SHmax>Sv>SHmin, and below about 2500 m Sv>SHmax>SHmin. SHmax appears to be oriented NE-SW, approximately perpendicular to the strike of Rocky Mountain thrust faults, except over the Peace River Arch and other basement uplifts that appear to refract the stress trajectories. Hydraulic fractures will propagate along planes normal to the least principal stress. Thus, above about 350 m such fractures will be horizontal, and below that depth they will be vertical and oriented parallel to SHmax. Knowledge of the stress configuration will assist directional drilling and planning of waterflood well configurations. This knowledge is also essential for planning multifractured inclined wells, such as might economically drain Deep Basin tight gas sands. Anisotropic horizontal principal stresses may have affected the Western Canadian Basin since the onset of the Laramide orogeny and induced non-uniform horizontal permeability fabrics in Mesozoic sandstones. The Western Canadian Basin is part of a widespread North American midcontinent stress province that exhibits a common orientation of compressive stresses. It is speculated that this stress regime is largely caused by NE-directed drag exerted on the base of the lithosphere by a mantle convection cell which upwells beneath western North America. REGIME DE TENSION DU BASSIN SEDIMENTAIRE DE L'OUEST CANADIEN, APPLICATION A LA PRODUCTION D'HYDROCARBURES RESUME Dans le bassin sedimentaire de l'ouest canadien, des mesures de surcarottages de forages, des fractures hydrauliques, des plans de glissement et des fracturations/ecroulements de puits suggerent un regime de tension ou SHmax>SHmin>Sv de la surface a 350 m de profondeur, SHmax>Sv>SHmin de 350 m a 2500 m de profondeur et Sv>SHmax>SHmin en-dessous de 2500 m de profondeur. SHmax aurait une orientation nord-est/sud-ouest, a peu pres perpendiculaire a la trace des chevauchements des Montagnes Rocheuses, sauf au-dessus du Peace River Arch et d'autres soulevements de socle qui semblent refracter les trajectoires de tension. Les fractures hydrauliques se propagent le long des plans perpendiculaires a la composante minimale de tension. De telles fractures seront ainsi horizontales au-dessus de 350 m de profondeur, et verticales paralleles a SHmax en-dessous. La connaissance des configurations de regimes de tension faciliterait les forages orientes ainsi que la planification des forages d'injection. Ces donnees sont aussi essentielles pour planifier les puits inclines avec fractures a orientations multiples tels qu'ils puissent drainer economiquement les gres peu permeables du Deep Basin. Le bassin sedimentaire de l'ouest canadien aurait ete soumis a des tensions a composante principale horizontale et anisotropique depuis le debut de l'orogenese laramienne; ceci aurait produit un regime a permeabilite horizontale tres peu uniforme au sein des gres mesozoiques. Le bassin sedimentaire de l'ouest canadien fait partie d'une province au centre du continent nord-americain ayant une composante de compression commune. Le regime de tension serait cause, en majeure partie, par une cellule de convection du manteau remontant endessous de l'Amerique du Nord et trainant la base de la lithosphere vers le nord-est. Traduction: Andre Zolnai et Jean Pelletier
The development of vein and rock textures by tensile strain crystallization
The characteristics of fibrous veins of gypsum and other minerals are described and it is concluded that the growth of the fibres kept pace with the dilation of the veins because fluid pressures were in excess of lithostatic pressures but less than the combined lithostatic pressures and tensile strengths of the fibres. Crystallization in the regions of greatest tensile strain in the fibres would be promoted by the greater probability of atoms being accommodated in the crystal structure. The free energy associated with the crystal dislocations which are likely to be concentrated in these regions would contribute to the crystallization process and allow it to proceed at very low levels of supersaturation. Crystallization during tensile strain explains the common occurrence of strain effects such as undulose extinction and dislocation planes in fibrous crystals. It is suggested that polycrystalline aggregates may deform under triaxial stress by pressure solution of the grains on planes approximately perpendicular to the direction of greatest stress and simultaneous crystallization of elongate crystals in the direction of maximum extension from the points of concentrated tensile strain. Tensile strain crystallization may be an important mechanism in the development of penetrative preferred orientations in metamorphic rocks.