Wireline Logging Unit

Overview

A wireline logging unit lowers measurement tools into a borehole on an armored cable, then records formation properties as the tools are pulled back up. The cable does two jobs at once: it carries the mechanical load of the tool string, and its insulated conductors send power down to the tools and bring telemetry back to the surface. Because the recorded curves only have value when they are tied to true depth, the unit measures cable depth and tension at surface with a calibrated sheave and a load cell. Everything mounts on a truck so the unit can be driven to the well and rigged up over the wellhead in a few hours.

The unit is built from nine subsystems. The Cable Winch and Drum stores the cable, the Winch Drive and Brake spools it under controlled tension, the Levelwind Assembly lays it evenly on the drum, the Measuring Head reads depth and tension, the Cable Head and Weak Point connects the cable to the downhole tools, the Slip-Ring Collector passes the conductors off the spinning drum, the Acquisition System records the data, the Hydraulic Power Pack supplies hydraulic and electrical power, and the Truck Deck and Cabin carries the lot on the truck.

Cable and winch

The heart of the unit is the Armored Logging Cable. A multiconductor cable wraps seven insulated copper conductors around a central core, then surrounds them with two contra-helically wound layers of galvanized plow-steel armor: the Inner Armor Wire and the Outer Armor Wire. The outer armor carries most of the load and takes the abrasion against the wellhead, while the inner armor balances the torque so the cable does not spin up under tension. A monocable variant uses a single conductor for simpler, cheaper tools.

The cable winds onto the Drum Barrel, a rolled steel cylinder closed by two Drum Flange discs and turning on a forged Drum Shaft. The shaft runs in Ball Bearing units in the Winch Frame, sealed against mud and rain by Oil Seal elements. A full drum of 30,000 ft of cable is heavy, so the frame and the truck deck are sized for the static and dynamic loads of fast spooling.

How the winch is driven

The drum is turned by the Winch Drive and Brake. A Hydraulic Drive Motor, an axial-piston unit built around a Hydraulic Motor Body and a Piston and Swashplate Set, takes oil flow from the power pack and turns it into torque. That torque passes through the Reduction Gearbox, which uses several Helical Gear Pair stages in a Gearbox Housing, and then through a Chain Drive to the drum shaft. The operator controls line speed by metering the oil flow, so the cable can be paid out fast on the way down and pulled at the slow, steady speed that logging requires.

Tension control matters because the cable can be parted by overpull or birdcaged by running slack. A Brake Disc on the drum shaft, clamped by two Brake Caliper units, holds the load when the drum is stopped. The operator reads tension on the console and brakes before the load reaches the cable rating.

Depth, tension, and the cable head

Depth comes from the Measuring Head, a frame of sheaves hung over the wellhead. The cable runs over the Upper Sheave and then the calibrated Measuring Sheave, whose circumference is known. A Depth Encoder, built on a Bare PCB with SMD Passive (R/C/L) reading a Encoder Disc, counts the sheave rotations and converts them to feet of cable travel. A Tension Load Cell at the sheave mount, preloaded by Coil Spring elements, reads the line tension. Both feed the cabin through Connector terminations.

At the bottom of the cable, the Cable Head and Weak Point connects to the tool string. Its Rope Socket anchors the armor wires and carries the load, while a Pin Connector mates the conductors to the tool. A calibrated Weak Point is built into the head so that if a tool sticks, the cable parts at a known overpull and leaves a clean fishing top rather than tearing the cable somewhere up the hole.

Conductors, acquisition, and power

The drum spins, but the cabin wiring does not, so the Slip-Ring Collector bridges the two. A Slip-Ring Stack stack on the drum shaft, wiped by a Brush Block, passes each conductor through a sealed Collector Housing to the cabin Wire Bundle.

In the cabin, the Acquisition System does the recording. The Acquisition Computer, running an Microcontroller real-time controller, samples the depth, tension, and tool channels through its Acquisition Board. The Telemetry Interface modem couples digital data onto the cable conductors, switching channels with a Relay bank, and the Tool Power Supply supply sends regulated DC down the line to run the tools. The engineer works at the Operator Console, reading two LCD Panel displays and commanding the winch.

The Hydraulic Power Pack feeds all of this. A Hydraulic Pump drives the winch through the Control Valve, cooled by the Oil Cooler and fed from the Hydraulic Oil Tank, with Pressure Sensor units watching system pressure. A AC Generator built from a Stator Assembly and Rotor Assembly supplies cabin AC power through the Power Supply.

Deck, variants, and use

The whole unit rides on the Truck Deck and Cabin, a welded Deck Frame on a heavy truck chassis. Four Stabilizer Outrigger legs level the truck, a folding Sheave Mast positions the measuring head over the well, and the Cabin Shell keeps the Acquisition System electronics and the operator at working temperature with a Heating Element and HVAC.

Units are configured for the well they serve. Open-hole logging units run resistivity, porosity, and sonic tools to map the formation. Cased-hole units run cement-bond and production-logging tools. Offshore and skid-mounted variants drop the truck and mount the winch on a platform skid. The smaller slickline variant uses a plain wire with no conductors for mechanical work, so it carries no acquisition system at all.