S-wave splitting analysis of 4-C VSP in Altamont-Bluebell field

Khaled Al Dulaijan, Gary F. Margrave

The 4-C VSP was acquired within Bluebell Field, the eastern portion of Altamont-Bluebell field in northeastern Utah. Altamont-Bluebell field is within the Uinta Basin, and is considered an unconventional reservoir in the sense that natural fractures act as fluid storage and conduits in the tight sandstones and carbonates. Information related to fracture orientation and intensity is vital for the development of such reservoirs. S-wave splitting can be useful for fracture-induced anisotropy. Therefore, this paper utilizes S-wave splitting to estimate the direction and intensity of fractured-induced anisotropy within the three main reservoirs using 4-C VSP data.

S-wave analysis is carried using Alford (1986) 4-C rotation to separate fast and slow modes. This method assumes that the symmetry axis is vertically invariant. In order to overcome this assumption, a layer stripping technique was applied using Winterstien and Meadows (1991).