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GEOREF RECORD

Seismic reconstruction of the in situ anisotropic stress field for caprock integrity in the Athabasca Oil-Sands Basin, Canada

Draga A. Talinga and Carmen C. Dumitrescu
Seismic reconstruction of the in situ anisotropic stress field for caprock integrity in the Athabasca Oil-Sands Basin, Canada
Interpretation (Tulsa) (February 2019) 7 (1): T221-T229

Abstract

In the Athabasca Basin of Alberta, Canada, the Lower Cretaceous McMurray Formation reservoir is overlain by the Clearwater Formation, a regionally continuous layer composed predominantly of shales with interbedded mudstones. The shales form the reservoir caprock and have the role of blocking the vertical migration of the steam from thermal oil production by confining the stresses and the deformations. We have developed a new method for the 3D seismic reconstruction of the anisotropic stress field, which accounts for the formation pore pressure and the effective stress. We integrated anisotropy estimated from dipole sonic logs with formation pore pressure data from piezometers and elastic properties obtained from multicomponent seismic inversion. The method combines the Terzaghi effective stress with the Schoenberg and Sayers elastic stiffness matrix for horizontal transversely isotropic (HTI) fractured materials. The key points of this method are the estimation of the formation pore pressure in the abnormal regime of the Clearwater Formation, the normal fracture weakness parameter (based on constraints on the compressional velocity of the intact rock under the HTI assumption), and the 3D seismic anisotropic stress field. We expressed the total vertical stress as the weight of the overlying formations, and the total minimum and maximum horizontal stresses as a combination of the total vertical stress, normal fracture weakness, formation pore pressure, Biot-Willis coefficient, and Lame elastic constants. The effective principal stresses are estimated from the equivalent total principal stresses and the formation pore pressure multiplied by the Biot-Willis coefficient. We observed excellent consistency between the calculated total minimum horizontal stress and mini-frac values. This new method for the 3D seismic reconstruction of the anisotropic stress field allows for the assessment of the caprock integrity and for operational savings based on a reduced number of mini-frac measurements, and it can be used for time-lapse stress estimation within the thermal production reservoir.


ISSN: 2324-8858
EISSN: 2324-8866
Serial Title: Interpretation (Tulsa)
Serial Volume: 7
Serial Issue: 1
Title: Seismic reconstruction of the in situ anisotropic stress field for caprock integrity in the Athabasca Oil-Sands Basin, Canada
Affiliation: Terra-IQ, Calgary, AB, Canada
Pages: T221-T229
Published: 201902
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 25
Accession Number: 2019-034010
Categories: Economic geology, geology of energy sourcesApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Technical papers
Illustration Description: illus. incl. sect., strat. cols., sketch maps
N57°00'00" - N59°30'00", W111°30'00" - W102°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 2019
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