Cementing forms an essential part of well construction as it supports the casing and provides hydraulic sealing. Wireline (WL) sonic tools have been providing the cement evaluation (CBL/VDL) for more than 50 years. Quantitative cement evaluation is becoming increasingly important in the industry to verify well integrity and zonal isolation. There has been a growing interest in providing cement bond quality quantitatively with LWD sonic tools owing to its plethora of benefits over wireline logging, such as rig time saving, tool conveyance, less tool eccentering effect and timelapse evaluation. However, there is also an LWD specific challenge that has for long hindered the ability to measure quantitative bond index i.e. drill collar contamination which limits the range of cement bond evaluation with the conventional amplitude-based approach. Deriving a characteristic correlation of attenuation measurement against the bond index was one of the key components to overcoming the limitation of amplitude-based. A new hybrid processing approach combining amplitude and attenuation was established for full-range cement bond evaluation. Schlumberger's LWD multipole sonic Cement Evaluation Service delivers the industry's first quantitative bond index answer product on LWD platform. The quantitative bond index becomes even more critical in offshore and deepwater markets.
This paper discusses, in brief, the technology and associated challenges in delivering industry's first quantitative bond index and showcases the result for one of the deepwater well. A subsequent comparison of LWD multipole sonic cement evaluation results with conventional WL CBL-VDL further corroborates the reliability of the result. The performance of the industry's first LWD bond index derived using LWD multipole sonic from around the globe has demonstrated that it can be expected to show abundant success in expanding the LWD utilization globally