An innovative technique orients and centers wireline toolstrings in the wellbore to ensure high-quality data acquisition. The system comprises wheeled carriages and angled guides and takes a holistic approach to wireline tool conveyance, reducing drag while ensuring optimum sensor positioning and orientation for each logging measurement.
Correct positioning is achieved through management of the tool center of gravity relative to the wheel axes. Positive toolstring orientation with ultralow-friction wheeled carriages replaces traditional positioning accessories such as bow-spring centralizers and/or powered multiarm calipers. The system improves data quality and enables gravity descents to extreme deviations (up to 80°) that were previously the domain of logging-while drilling, drillpipe, and tractor conveyance.
The oriented conveyance system provides sonic centralization, prevents rotation of the formation imager, and reduces stick/slip motion, which is essential for obtaining high-resolution data.
Centralization of the array sonic tool is critical for data quality, irrespective of whether the requirement is simply sonic slownesses or involves more complex dipole anisotropy and reflectivity analysis. It is equally important that the logging tool is parallel to the wellbore with no sag or tilt. In deviated wells, it is often difficult to optimize standoffs and bow-spring centralizers to provide centralization while maintaining smooth tool motion for quality data. In addition, powered multiarm calipers introduce additional drag and increase the likelihood and severity of stick/slip. Smooth tool motion is critical when sonic imaging data is acquired to examine fractures and structure in the far field.
Centralizing sonic tools by using wheeled carriages remedied these problems and resulted in improved data quality in a recent well with 79° deviation. Examination of the slowness dispersion analysis and single-sensor azimuthal receiver data of the array sonic along with finite-difference modeling of the waveforms verify the effectiveness of the centralization.
Excessive stick/slip of wireline toolstrings causes replication of high-resolution subsurface data and small intervals are missed entirely, resulting in a mismatch between actual and recorded depth intervals. The resulting degradation of array sonic measurements and borehole image quality is not recoverable. The wheeled carriages facilitate smooth tool movement, resulting in improved-quality data.
Tool rotation, due to the release of cable torque, often results in overlapping images from toolstrings with axially spaced pad sensors in contact with the wellbore wall. The new system locks the tool into a set orientation, preventing rotation.
The improvements in data quality combined with efficiency enhancements and the reduction of risk during wireline logging deliver a superior method of conducting operations. Examples are shown for assessment of valid sonic and borehole image results.