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AAPG Bulletin

Abstract

AAPG Bulletin, V. 93, No. 11 (November 2009), P. 1503-1516.

Copyright copy2009. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/08250909019

Fracture characterization at multiple scales using borehole images, sonic logs, and walkaround vertical seismic profile

Romain Prioul,1 Jeroen Jocker2

1Schlumberger-Doll Research, One Hampshire Street, Cambridge, Massachusetts 02139; [email protected]
2Schlumberger-Doll Research, One Hampshire Street, Cambridge, Massachusetts 02139; [email protected]

ABSTRACT

We present a quantitative forward-modeling methodology to link and interpret several measurements relevant to mechanical properties of fractures such as borehole images, sonic Previous HitanisotropyNext Hit logs, and borehole seismic Previous HitanisotropyNext Hit. The analysis is applied to a case study from a north African tight gas field using data from a vertical well. Two studies are conducted independently using the same geological fracture data to model fracture-induced Previous HitanisotropyNext Hit. In the first study, we use the orientation of the natural and drilling-induced fractures interpreted on the image log to model the azimuthal fracture-induced Previous HitanisotropyTop at the sonic scale. The mechanical effects of natural and drilling-induced fractures are treated using different compliance parameters for each fracture type. We show that modeled sonic fast shear azimuths could be biased by the presence of noncompliant fractures in each fracture type, and we propose an empirical selection criterion to reject noncompliant fractures prior to compliance estimation. Then, we estimate the fracture compliances and confirm that natural open fractures have larger compliances than drilling-induced fractures. In the second study, we apply interpreted borehole images toward modeling of the azimuthal vertical seismic profile (VSP) attributes as a function of source azimuthal position. Natural fractures inside a window of height, h, and located at depth, d, are included, and several volume sizes and positions (i.e., h and d) are considered. We find a good agreement between modeled and observed transverse-over-radial displacement trends using natural fractures within windows located at the depth of the VSP receiver, and having window heights on the order of one to two VSP shear wavelengths.

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