Water-flooding and consolidation of reservoir chalk - effect on porosity and Biot's coefficient
Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
Standard
Water-flooding and consolidation of reservoir chalk - effect on porosity and Biot's coefficient. / Gram, Tobias B.; Ditlevsen, Frederik P.; Mosegaard, Klaus; Fabricius, Ida L.
I: Geophysical Prospecting, Bind 69, Nr. 3, 19.11.2020, s. 495-513.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
Harvard
APA
Vancouver
Author
Bibtex
}
RIS
TY - JOUR
T1 - Water-flooding and consolidation of reservoir chalk - effect on porosity and Biot's coefficient
AU - Gram, Tobias B.
AU - Ditlevsen, Frederik P.
AU - Mosegaard, Klaus
AU - Fabricius, Ida L.
PY - 2020/11/19
Y1 - 2020/11/19
N2 - Improved oil recovery from chalk reservoirs by water-flooding may cause mechanical weakening and change in elasticity. Confined compressive strength testing of chalk from a North Sea reservoir was done in water-saturated and oil-saturated conditions. During testing, elastic wave velocities were sampled by ultrasonic transducers, so that subsequently Biot's coefficient could be modelled. The porosity declined via an 'elastic phase', a 'transitional phase', an 'elastoplastic phase' and a 'strain hardening phase', but Biot's coefficient indicates that these terms may be partly misleading. In the 'elastic phase', porosity and Biot's coefficient decrease, indicating elastoplastic deformation. In the 'transitional phase', Biot's coefficient increases as a reflection of breaking contact cement (pore collapse), whereas Biot's coefficient remains stable in the 'elastoplastic phase', indicating elastic deformation on the virgin curve. Plastic deformation takes place during phases of creep, where both porosity and Biot's coefficient decrease. Similarly, in the 'strain hardening phase', both porosity and Biot's coefficient decrease as a reflection of elastoplastic deformation. For chalk with 45%-47% porosity, the 'transitional phase' begins at 8 MPa axial stress when water-saturated and at 12 MPa when oil-saturated. For chalk with 41%-43% porosity, the corresponding stresses are 16 and 20 MPa. For chalk with 32%-36% porosity, the corresponding stresses are 23 and 31 MPa. Chalk samples with irreducible water saturation and movable oil were water-flooded. They yield at stresses close to corresponding oil-saturated samples, but after flooding show compaction trends not significantly different from the water-saturated samples. Water-flooding promotes pore collapse as reflected in an increasing Biot's coefficient. The consequent softening effect on acoustic impedance is small as compared with the effect of increasing fluid density. With respect to 4D seismic, water-flooding causes distinctly higher acoustic impedance and Poisson's ratio irrespective of compaction.
AB - Improved oil recovery from chalk reservoirs by water-flooding may cause mechanical weakening and change in elasticity. Confined compressive strength testing of chalk from a North Sea reservoir was done in water-saturated and oil-saturated conditions. During testing, elastic wave velocities were sampled by ultrasonic transducers, so that subsequently Biot's coefficient could be modelled. The porosity declined via an 'elastic phase', a 'transitional phase', an 'elastoplastic phase' and a 'strain hardening phase', but Biot's coefficient indicates that these terms may be partly misleading. In the 'elastic phase', porosity and Biot's coefficient decrease, indicating elastoplastic deformation. In the 'transitional phase', Biot's coefficient increases as a reflection of breaking contact cement (pore collapse), whereas Biot's coefficient remains stable in the 'elastoplastic phase', indicating elastic deformation on the virgin curve. Plastic deformation takes place during phases of creep, where both porosity and Biot's coefficient decrease. Similarly, in the 'strain hardening phase', both porosity and Biot's coefficient decrease as a reflection of elastoplastic deformation. For chalk with 45%-47% porosity, the 'transitional phase' begins at 8 MPa axial stress when water-saturated and at 12 MPa when oil-saturated. For chalk with 41%-43% porosity, the corresponding stresses are 16 and 20 MPa. For chalk with 32%-36% porosity, the corresponding stresses are 23 and 31 MPa. Chalk samples with irreducible water saturation and movable oil were water-flooded. They yield at stresses close to corresponding oil-saturated samples, but after flooding show compaction trends not significantly different from the water-saturated samples. Water-flooding promotes pore collapse as reflected in an increasing Biot's coefficient. The consequent softening effect on acoustic impedance is small as compared with the effect of increasing fluid density. With respect to 4D seismic, water-flooding causes distinctly higher acoustic impedance and Poisson's ratio irrespective of compaction.
KW - Rock physics
KW - 4D
KW - Deformation
KW - Porosity
KW - Partial saturation
KW - PETROLEUM
U2 - 10.1111/1365-2478.13047
DO - 10.1111/1365-2478.13047
M3 - Journal article
VL - 69
SP - 495
EP - 513
JO - Geophysical Prospecting
JF - Geophysical Prospecting
SN - 0016-8025
IS - 3
ER -
ID: 252878009