Conducting logging-while-drilling (LWD) for cement evaluation has obvious economic advantages in terms of reduced rig-time and cost, as well as providing the potential for making time-lapse measurements spaced over the duration of a bit-run. However, the design constraints imposed on LWD tools by the mechanical strength requirements of the BHA, frequently mean that LWD acoustic measurements are contaminated by tool-borne modes, even when the collar between the transmitter and receivers is modified to attenuate them, often resulting in qualitative answers for cement evaluation. In this paper, an enhanced solution is described which involves estimating and subtracting the tool-borne mode for quantitative cement evaluation. The tool-borne mode is first predicted by phase-shifting and attenuation correcting all the data in the array. This estimate is then subtracted from the raw recording at a reference receiver. The effect of the removal algorithm on casing-borne modes is predictable and can be accounted for by a correction factor. Field data processing results suggest the proposed method can provide an accurate bond index over the full range from 0 to 1.
Presentation Date: Wednesday, September 18, 2019
Session Start Time: 1:50 PM
Presentation Time: 4:20 PM
Presentation Type: Oral