Calculating Unconfined Rock Strength from Drilling Data


It is critical to obtain the rock strength parameters along the wellbore. Rock strength logs are used to conduct different types of analysis such as preventing wellbore failure, deciding on completion design methods and controlling sand production. One source of data which is often overlooked in calculating rock strength is drilling data. To utilize the drilling data in calculating strength, correlations are developed from inverted rate of penetration models. From these models unconfined compressive rock strength can be calculated from drilling data. The rate of penetration models takes into account operational drilling parameters, bit types/designs and geological formation information. Results from various onshore and offshore fields verify that drilling based rock strength compares to other methods of estimating rock strength. The big advantage using drilling data is that rock strength can be calculated for all hole sections, less expensive onshore wells and from old wells, where electrical logs or preserved core samples do not exist.

Meeting Name

1st Canada-US Rock Mechanics Symposium - Rock Mechanics Meeting Society's Challenges and Demands (2007: May 27-31, Vancouver, BC, Canada)


Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

Boreholes; Boring; Cements; Compressive strength; Drilling; Failure analysis; Mechanics; Offshore drilling; Offshore oil wells; Oil field equipment; Oil well logging; Quality assurance; Rock mechanics; Superconducting tapes; Well drilling; Design methods; Drilling datums; Drilling parameters; Geological formations; Hole sections; Offshore fields; Onshore wells; Rate of penetrations; Sand productions; Wellbore

International Standard Book Number (ISBN)


Document Type

Article - Conference proceedings

Document Version


File Type





© 2007 Society of Petroleum Engineers (SPE), All rights reserved.

Publication Date

01 May 2007

This document is currently not available here.