Stress Field Delineation using Well Log Data – A Case Study

Rakhi Arvind Pandey

doi:10.23953/cloud.ijaese.276

Abstract

The essentiality of stress field delineation in the subsurface arises in several contexts like well planning and monitoring to ensure safe drilling of a borehole. Work reported here concerns with methodology developed for delineating stress fields in rock strata using log data which includes crossed dipole and monopole acoustic data acquired in boreholes. Orientation of the principal stresses in the horizontal plane has been arrived at by computing relative azimuth of maximum and minimum stress directions with respect to a designated dipole transmitter’s axial orientation. Static Poisson Ratio and Static Young’s modulus have been computed using customized relationships with due care has been taken to factor-in fluid effects where compressible fluids are known to present within pore space of the rock. Stresses magnitudes and UCS model have been subjected to a validity check through prediction versus actual of presence / absence of breakouts (the latter from image data evidence) and the match is very good.

Highlights

Delineation of local stress field and its relationship between regional stress fields, gives the allimportant depth-wise behavior of magnitude as well as orientation of the principal stresses
Borehole images and drilling observations have been noted as fully corroborating model based predictions and Static Young’s Modulus, PR,UCS and Friction angle are validated by laboratory estimation based on cores cut in stratigraphic and lithological rock in a well currently under drilling and not necessarily a part of the case study reported
The work flows have been developed for exploration areas off Kutch-Saurashtra coast India [1].The case study presented involves 2 wells and well sections pertaining to tertiary as well as pre-tertiary have been made a part of the case study

Summary

Introduction

Delineation of local stress field and its relationship between regional stress fields, gives the allimportant depth-wise behavior of magnitude as well as orientation of the principal stresses. The distinguishing features of the work flows are modeling azimuthally anisotropic principal stresses in horizontal plane using fast shear and slow shear slowness and a realistic model of residual strains (due to residual tectonic stresses). Borehole images and drilling observations have been noted as fully corroborating model based predictions and Static Young’s Modulus, PR,UCS and Friction angle are validated by laboratory estimation based on cores cut in stratigraphic and lithological rock in a well currently under drilling and not necessarily a part of the case study reported. The work flows have been developed for exploration areas off Kutch-Saurashtra coast India [1].The case study presented involves 2 wells and well sections pertaining to tertiary as well as pre-tertiary have been made a part of the case study. Two wells have been analyzed; general information of the same is given below

Methods

Results

Conclusion