Using memory-based logging tools positioned within the drill string, GR Energy Services offers logging-while-tripping (LWT†) services to obtain openhole logs quickly and with lower risk than using conventional wireline or logging-while-drilling techniques. Log data are recorded during the pipe trip out of the well, and tools and sources are always retrievable.
LWT is a commercially proven, patented formation evaluation technique. Wireline-quality openhole logs are acquired in memory, immediately after drilling has been completed, while the drilling assembly is tripped to surface. LWT measurements, including Gamma Ray (GR), Spectral Gamma Ray (SGR), Compensated Neutron (CN), Compensated Density (CD) and Dual Induction (DUIN), are obtained with standard openhole API-calibrated logging devices and meet all requirements for porosity and resistivity measurements. The battery-operated, memory-based tools are lightweight with a small outside diameter, allowing simple deployment within specialized LWT drill collars.
The LWT collar, which is inserted into the drill string on the last bit trip or on the planned reamer run, does not require any change in drilling plans or extra rig time to change to a specialized BHA. LWT tools are deployed (pumped down) at the well TD stage and log untethered in memory during the normal pipe trip out. Virtually no additional rig time is needed.
During the operation the logging tools reside at all times inside the drill pipe and can be fished, eliminating the risk of damaging or losing the tools and radioactive sources in the hole. While deploying the tools and measuring, the operator has full well control.
Unlike MWD and LWD tools, LWT tools are not a permanent part of the bottomhole assembly, but instead are deployed and retrieved from the drill string only when log data are required. Operators get the benefit of significant cost savings in openhole data acquisition because
- There is virtually no additional rig time to acquire logs.
- Lost-in-hole charges are significantly lower than wireline or LWD.
- There is no risk of tool sticking.
The LWT collars are positioned as close to TD as possible, and the BHA configuration is carefully reviewed by the GR technical team before rig-up. After reaching TD with the LWT collars in the bottomhole assembly, the tools are deployed in the drill pipe and pumped down. Once landed, the rig pumps a mud pill, if required, and trips out at logging speed. The rig can circulate, rotate or reciprocate pipe with the tools landed in the collar.
The comparison of conveyance options shows how LWT services outperform alternatives.
This comparison overlay of LWT and conventional wireline data acquired in the same well shows an excellent match.
†LWT is a mark of Cordax Evaluation Technologies Inc.