To better understand their reservoir in a highly deviated offshore well, the operator required advanced measurements in an appraisal well over and above those normally recorded with basic LWD measurements. The data required to better characterize the reservoir were electrical image logs, dipole shear sonic imaging, high-resolution magnetic resonance measurements, and formation pressure tests as well as pressure/volume/temperature (PVT) fluid samples, all to be collected in oil-base mud. The Operator and Service Company were looking for efficient alternatives to a pipe-conveyed logging operation.
After a thorough study of well details, modelling of required tractor force, and close collaboration between the operational teams of both the operator and service company, it was determined that a conveyance system including the latest generation all-terrain tractor and high-strength cable would be suitable for this operation. Compared to running on drillpipe, tractor conveyance offered benefits for this operation in terms of rig time, flexibility, and safety. The 50-m and 4,513 lbm fluid sampling toolstring used for the operation included six pairs of tractor drives, all required logging equipment, and an electronically controlled weakpoint deployed with an 18,000 lbf high-tension conveyance package.
Petrophysical measurements as well as downhole formation testing and sampling were all achieved successfully using the all-terrain tractor conveyance in four logging runs, with a total tractored distance of 6,800 m in a formation with unconfined compressive strength ranging from below 5,000 psi to as low as 600 psi. The data and samples were acquired in five logging runs across the entire reservoir interval with a maximum tension of 10,500 lbf. The total operational time of 70 hr represented a time saving of approximately 72 hr compared to a pipe-conveyed operation with the same logging equipment in this setting. Successful deployment of this tractor technology offers alternatives to operators in the region for formation evaluation.