A well that has produced for fifteen years rarely has one clean string left to inspect. There is tubing inside casing, casing inside surface pipe, and on many older completions a liner behind that. Pulling the tubing to log the casing is a workover an operator struggles to justify on a well that still pays. The electro-magnetic interference tool exists for that situation: it runs through the tubing on wireline, measures the wall of every concentric string within reach, and returns a corrosion map without a single joint being pulled. The decision it serves is blunt - keep producing, or mobilize a rig.
What the Electro-Magnetic Interference Tool Reads
The tool drives an alternating field into the pipe and watches the phase and amplitude that come back. Wall loss shifts the phase, a coupling shifts it differently, and a crack disturbs it locally. Because the field passes through steel instead of stopping at the first surface, one pass returns information from each concentric string. The tool records 127 curves across a measurement range of 60 to 473 mm, which is what lets a single run cover a 4-1/2 inch liner inside 7 inch casing inside 9-5/8 inch surface pipe. The result is not a photograph. It is a set of curves that an analyst fits to a wall model, and the model is only as good as the calibration pass recorded in the same well on the same run.
Wall Accuracy Falls With Each String
Accuracy is quoted per layer, and the numbers matter when the answer decides a workover. On the first string, with wall up to 20 mm, the tool resolves 0.190 mm, roughly 0.0075 inches. On the second string the figure is 0.254 mm and on the third it is 1.52 mm. That pattern is physics rather than a defect: the signal crosses more steel and more annulus fluid before it returns. In the field the first string gets a corrosion map good enough to plan a squeeze, the second gets a profile good enough to plan a re-completion, and the third gets a flag that says whether the outer casing is still carrying load. Quoting a third-string number to the nearest millimetre would be a mistake the report should never invite.
Running the Electro-Magnetic Interference Tool on Wireline
The maximum logging speed is 400 meters per hour, which is 22 feet per minute, and the ceiling comes from the sampling rate rather than from the wireline. Crews usually run slower across the interval of interest and faster through good pipe, so a 1,300 feet section with two known corrosion zones becomes a 4 to 6 hour job including rig-up. Three things decide whether a pass is worth repeating:
Whether the caliper and the interference pass agree on the same joint.
Whether centralization held through the deviation.
Whether the calibration pass was recorded in the same string.
A repeat pass that contradicts the first is far cheaper than a workover built on the wrong answer.
Rig-Up on a Producing Well
The tool is 43 mm in diameter, 1750 mm long and 7 kg in weight, so it handles like a short production logging string rather than a casing inspection skid. The envelope is 100 MPa, or 14,500 psi, at 175 °C, which covers most completions that are still making gas. On a live well the lubricator has to swallow the tool plus its centralizers, and the wireline crew wants a shut-in valve above the tool in case the grease seal fails. The wellsite routine is ordinary work: pressure test the lubricator, record the shut-in pressure, run in at a controlled speed, and tie depth correlation to a collar the casing tally already knows.
Turning the Map Into a Decision
The sentence at the top of the report matters more than the curve set: maximum wall loss, its location, and whether the remaining wall still carries the burst and collapse loads the well needs. On a water injector with pitting on the first string, a 30 percent wall loss over 20 feet may move the well from unrestricted injection to a pressure-limited regime instead of to a rig. On a gas well with CO2 in the stream the same number may justify the workover. The tool supplies the measurement and the operator supplies the consequence.
An electro-magnetic interference tool does one thing well: it turns a guess about unseen pipe into a measured wall profile across several strings in a single wireline run. When the alternative is pulling tubing to answer the same question, the decision changes before a rig is ever called.
For more information, please contact China Vigor at info@vigorpetroleum.com or call +0086 29 81161513.
