A comparison of logging while drilling (LWD) and wireline acoustic measurements

The instruments used to measure borehole acoustic data can be classified as either wireline or logging while drilling (LWD). The wireline tool measures formation speeds after the borehole is drilled, and the LWD tool measures formation speeds while the borehole is drilled. This thesis focuses on comparing the data collected by these tools and how formation properties affect their measurements. LWD and wireline measurements taken from the same borehole are compared. Discrepancies in estimated shear and compressional velocities, as calculated by time semblance methods, were found between the two data sets. We modeled radially layered formations with increasing or decreasing radial velocity profile to estimate the acoustic measurement penetration for each tool. We reprocessed sections of the data using frequency semblance methods and compared with layered model results. We found that a frequency-domain analysis is feasible and reduces the overall difference between the LWD and wireline shear and compressional velocity estimates. The remaining discrepancy can be explained by the different radial depths of penetration of these two tools, which naturally leads to a difference in the velocity estimates when there is a radial gradient in the velocity profile.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2006

Author dc:creator

• Briggs, Victoria Alice, 1974-

Advisor dc:contributor.advisor

• M. Nafi Toksöz.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/37981

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/37981