Running a production profile through tubing means the instrument string must first pass every nipple, safety valve and restriction above the reservoir. Once it is below the deepest restriction, the string has to sample a borehole whose diameter may be several times its own. Conventional production logging tools resolve this conflict by offering five body diameters from 1.18 inches to 1.69 inches, each carrying a different sensor payload, so the configuration decision is made against the completion geometry rather than against the measurement wish list.
Matching Body Diameter to the Completion Restriction
The VPLT range covers 30, 32, 35, 38 and 43 mm bodies, equal to roughly 1.18, 1.26, 1.38, 1.50 and 1.69 inches. The narrowest body passes the tightest through-tubing restriction but accepts the shortest sensor complement; the 43 mm body, at 1.69 inches, is the only one that can carry the full suite, including an ultrasonic flowmeter, an X-Y caliper, an optical gas holdup probe and a neutron section.
30 mm and 32 mm bodies: restricted through-tubing work, reduced sensor count, 80 MPa rating
35 mm and 38 mm bodies: balanced payload at 100 MPa
43 mm body: full sensor suite, 100 MPa, suited to casing profiling below the tubing tail
Every size in the range is rated to 175 degrees Celsius, which is about 347 degrees on the Fahrenheit scale, so temperature is rarely the selection driver; diameter and pressure are.
Conventional Production Logging Tools and the Sensor Payload
Sensor complement scales with body size because each measurement sub occupies length and bus address on a shared instrument bus. A telemetry sub acts as the communication bridge: it carries the cable-bus and instrument-bus interfaces, a main controller and a step-down DC-DC section, acquires data from each sub over the instrument bus, packs the frames and sends them to the surface chassis, while the surface system returns commands. That full-duplex arrangement lets one operator reconfigure gains and sampling rates without pulling out of hole, which matters when the first pass shows an unexpected flow regime.
Flowmeter Selection Across Five Body Sizes
Flow measurement drives most of the interpretation, and the string can carry more than one rotor. A continuous spinner profiles variable cross-sections; an in-line spinner with a high-temperature, fouling-resistant plastic impeller can sit anywhere below the telemetry sub and logs inside tubing; a fullbore spinner opens below the tubing tail to sample the whole casing section. Published spinner specifications put the apparent threshold of a fullbore rotor near 4.6 feet per minute and that of a shrouded in-line rotor near 12 feet per minute, so in low-rate wells the larger rotor is the safer choice, while in deviated sections an in-line unit is carried as backup because debris settling along the low side can damage an unprotected fullbore cage.
Depth Control: Casing Collar Locator and Gamma Ray Correlation
A flow profile is only useful if the depths are right. The casing collar locator fixes the string against known collar depths, and the gamma ray curve ties the profile to the formation, giving a depth benchmark for both production and injection profiles and guiding perforation positioning. Pressure is measured with quartz or strain gauges, temperature with a platinum resistance probe, water holdup by capacitance and fluid density by a tuning-fork sensor that needs no radioactive source. An X-Y caliper adds borehole diameters on two axes, correcting the flow area where casing is deformed or the hole is washed out, and a spring centralizer with six bows keeps the string off the low side.
Conventional Production Logging Tools in Surface Readout and Memory Modes
Surface readout over monoconductor cable gives live quality control: the logging engineer sees whether flow has stabilised before committing to a full set of passes. Where surface access is restricted or the produced fluid is aggressive, a memory sub and battery sub replace the telemetry path and data is downloaded after the run. Communication is by Manchester or AMI code depending on body size, and cable head, flexible joint, swivel sub, weight bar, centralizer and release tool complete the mechanical string that carries the sensors to depth.
Sizing decisions determine what a production log can prove. Conventional production logging tools give five body diameters, a 175 degrees Celsius rating and a modular instrument bus, so the string can be matched to the completion instead of forcing the completion to accept a fixed tool.
For more information, please contact China Vigor at info@vigorpetroleum.com or call +0086 29 81161513.
