Slowness Reconstruction for Borehole Sonic Data
Jong Ha Lee(1), Toshifumi Matsuoka(1), Yuzuru Ashida(1), Di Cao(2) and Takeshi End(2)
(1) Kyoto University, Department of Earth Resource Engineering, Japan. (2) Schlumberger K. K., Japan.
Contacts: jhlee@tansa.kumst.kyoto-u.ac.jp (Jong Ha Lee)
Abstract
This paper introduces a refraction tomography technique to image near-borehole structures using Fresnel volume approach. The Fresnel zone wave path defined by a bundle of rays delayed by half a period to the exact ray is shaped up as weighting values around the exact ray path. The Fresnel zone wave path is calculated by simple secondary traveltime calculations. For the inversion, the weighting values assigned on the grids are used as they are to get the updating slowness for the algebraic reconstruction technique so that the exact ray tracing is not needed a t all. The initial model selection is the most agonizing step for the methods treating refracted waves since the result is sensitive to the initial guess. Adopting certain frequency band for the Fresnel zone wave path, by the blurring nature of the wave path, the reconstruction is enabled from a homogeneous model. By implementing a borehole sonic tool with some shots and successive receivers which acquires sonic data by moving along a borehole, numerical experiments were carried out on several models with near-borehole effect. The refraction tomography with Fresnel zone wave path turned out to be an effective method for the reconstruction of near- borehole formation slowness.
raeg2003@tansa.kumst.kyoto-u.ac.jp
Last modified: Wed Dec 25 16:49:13 2002