Fractured reservoir characterization using far offset VSP

Abstract

This paper discusses methodology and results of an azimuthal anisotropy study using converted PS waves. This research was initiated by the need to predict vertically fractured formations, expressed in the anisotropy of the subsurface. The study was aimed at detecting, by 3component VSP data, intervals with vertical fracturing and determining preferred fracture direction and fracture intensity. We suggest a technique, which utilizes converted wave energy generated by two or more offset shots fired at different directions and recorded by 3-component geophones along a vertical profile. The proposed technique was tested in well A of the Varandei field located in the north of Russia. Vertical fracturing was detected in two formations and confirmed by examination of cores.