ABSTRACT: Elastic wave propagation in a pre-stressed formation with a borehole

Wang, Xiuming, Kevin Dodd, and Li-Yun Fu , CSIRO Petroleum, Bentley, Australia

Horizontal tectonic stresses and overburden in a formation may cause stress-induced formation anisotropy. These issues have been treated by many authors [Renlie and Raaen, 1993; Carroll, 1979; Norris et al, 1994; Thurston, 1965; Zatsepin and Crapin, 1997]. It is important to distinguish the anisotropy caused by stress and by the others so that one may establish some ties between wave propagation and the stress amplitude as well as direction to predict formation stress or pressure. Recently, Sinha and Kostek et al (1996, 1997, 1999) used acousto-elasticity theory to simulate borehole wave propagation in laboratory experiments to investigate the effect of a horizontal stress on borehole waves . Also they calculated flexural and Stoneley modes by using a perturbation technique. They found that the horizontal stress causes flexural mode dispersion curves to cross over between minimum and maximum stress directions. This phenomenon could be used to identify the anisotropy caused by horizontal stress.

In our work, we will carry out a forward modeling of elastic wave propagation in pre-stressed medium by using acousto-elasticity theory in an anisotropic medium, and analyze how stress influences the wave propagation. Especially, the horizontal stress distribution in the vicinity of a borehole and the compressional- and shear-wave velocity distribution are calculated. Borehole waves excited by a monopole and dipole acoustic sources in pre-stressed formation are calculated. From these numerical modeling we will understand the effect of a horizontal tectonic stress on wave propagation in detail.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia