HR: 09:45h
AN: U41A-06    [Abstracts]
TI: Discrepancies Between LWD and Wireline Acoustic Logging Measurements in an Unconsolidated Formation: a Modeling Study
AU: * Chi, S
EM: shihong@erl.mit.edu
AF: Earth Resources Laboratory, Massachusetts Institute of Technology, E34-566 42 Carleton St., Cambridge, MA 02142 United States
AU: Briggs, V
EM: vbriggs@mit.edu
AF: Earth Resources Laboratory, Massachusetts Institute of Technology, E34-566 42 Carleton St., Cambridge, MA 02142 United States
AU: Burns, D
EM: burns@mit.edu
AF: Earth Resources Laboratory, Massachusetts Institute of Technology, E34-566 42 Carleton St., Cambridge, MA 02142 United States
AU: Rao, V
EM: rrao@mit.edu
AF: Earth Resources Laboratory, Massachusetts Institute of Technology, E34-566 42 Carleton St., Cambridge, MA 02142 United States
AB: Acoustic Logging-While-Drilling (LWD) significantly reduces drilling rig time in deepwater development than its wireline counterpart. It can also provide high-resolution formation velocity logs as wireline logging does in most situations. LWD measurements are critical in subsurface imaging, seismic-well tie, and wellbore stability. However, in an unconsolidated formation, data show both compressional and shear wave velocities by a LWD tool are slower than those obtained by a wireline tool. The discrepancies may result from differences in geometries, source-receiver offsets, operating frequencies, and off-centering of the tools and borehole conditions in which both measurements are made. To pinpoint the main cause of the difference and build confidence on application of LWD tools, we extend the propagator matrix method for simulation of acoustic multipole wireline measurements to acoustic LWD modeling in radially layered formations. Both LWD measurements and dispersion properties can be computed analytically. Time and frequency domain semblance techniques are also used to quantify depths of investigation of LWD and wireline tools in boreholes with radially increasing velocity profiles. Extensive modeling results show that the LWD tool investigates about half of the depth of the wireline tool does in this unconsolidated formation. To ensure accurate measurements of formation velocities, particularly shear wave velocities, in unconsolidated formations, a wireline or LWD tool operating at low frequency may be necessary.
DE: 0915 Downhole methods
DE: 0999 General or miscellaneous
SC: Union [U]
MN: 2005 Joint Assembly