A New Generation Crossed Dipole Logging Tool: Design and Case Histories

摘要

With the increase in deepwater exploration and productionand the advances in logging-while-drilling formationevaluation (along with the high rig costs) the wirelineformation evaluation is often limited to only one drill pipeconveyed logging run. A new monopole and crosseddipole acoustic logging tool was designed for the drill pipeconveyed environment. The robust mechanical design doesnot limit this sonic tool to the bottom of the tool string.NMR and pump-through formation testing tools can belocated in the logging string below this tool on drill pipe-conveyedlogging, or e-line conveyed logging.This tool was designed utilizing a systems approachand most of the functions of the tool are surfaceprogrammable. For example, the pulse shape, duration,amplitude, and frequency of the on-depth crossed dipolebender bar sources is programmable. Likewise, the level ofthe monopole output signal is also surface selectable. Thedigitization of the 96 waveforms of data per depth sampleis programmable for number of samples, sampling intervaland waveform compression. With 96 waveforms per depthsample, a logging speed of approximately 1800 ft/hr (30ft/min) can be achieved with a quad-combo logging suiteacquiring sonic data at two samples per foot.Case histories from a variety of formations demonstratethe tool’s capability to obtain monopole P wave data,monopole refracted shear data, crossed dipole flexuralwave slowness, and anisotropy. The followingrepresentative formations are included in the case histories:· near-zero porosity carbonate with refracted shearwave slowness and flexural wave slowness of lessthan 100 msec/ft· poro-plastic Gulf Coast sandstones and shales withflexural wave travel times exceeding 700 msec/ft· formations with natural fractures that are detectable bythe cross dipole flexural wave slowness and confirmedwith open hole image data· a shale section with approximately 650 psi of stressanisotropy