Methods of using Logs to Quantify Drillability
Correlations between sonic logs and the formation drillability for different lithology types have been developed from data taken from 10 wells in North America. The gamma ray log was used in conjunction with drilling data to calculate the drillability. The drillability from penetration rate models is back calculated from bit design and reported field wear in conjunction with meter by meter operating parameters, formation type and pore pressure. Then this drillability was correlated with sonic logs for different lithologies as defined by the gamma ray log. The different formation types clearly show different correlations for the normalized correlations between drillability and sonic logs. The non-homogeneous lithologies are also correlated and normalized to rock strength from the sonic logs where the percent formation type mixtures are determined from the gamma ray. Data from multiple wells is presented showing the accuracy of the presented approach where more then 100,000 data points were statistically analyzed and evaluated in the development of the equations presented herein. The drillability from inverted penetration rate models has been verified to give good representation of rock strength based on comparison with triaxial laboratory data and makes the use of this model more versatile. The correlations provide improved estimations of rock strength which can be used in drilling performance simulation and wellbore stability studies.
R. Andrews et al., "Methods of using Logs to Quantify Drillability," Proceedings of the Society of Petroleum Engineers Rocky Mountain Oil and Gas Technology Symposium (2007, Denver, CO), pp. 70-76, Society of Petroleum Engineers (SPE), Apr 2007.
The definitive version is available at http://dx.doi.org/10.2118/106571-MS
Society of Petroleum Engineers Rocky Mountain Oil and Gas Technology Symposium (2007: Apr, 16-18, Denver, CO)
Geosciences and Geological and Petroleum Engineering
Keywords and Phrases
Penetration rate models; Rock strength; Computer simulation; Gamma rays; Lithology; Pore pressure; Rock mechanics; Statistical methods; Drilling
International Standard Book Number (ISBN)
Article - Conference proceedings
© 2007 Society of Petroleum Engineers (SPE), All rights reserved.