Selecting a truck-mounted workover rig.

Start from the well program, not the model name.

A truck-mounted workover rig is selected from the operation it has to perform. The practical order is: define the workover depth and tubular size, calculate the heaviest string load, check the mast clearance, and only then compare power and chassis. Horsepower is a useful figure, but it is not the deciding one. Two rigs can share the same engine rating and still differ widely in depth, hook load and road behaviour, because those figures come from the drawworks, travelling block arrangement and chassis, not from the engine alone.

The examples used throughout this guide are the eight truck-mounted workover models in the ZYT range, from the 150HP entry unit to the 850HP ultra-deep well rig. Their published parameters show how the same selection logic works in practice.

Step 1: Define the workover depth and the tubing size.

Depth is the first filter because it sets the hoisting duty and the practical limit of the rig. In the ZYT range, workover depth is stated for a specific tubular size, usually 2 7/8" upset tubing or 73mm tubing:

If the well program lists both a workover depth and an occasional deeper intervention, compare the model against the deeper figure. The 350HP XJ350, for example, is rated 4,000 m for workover with 2 7/8" thicken drill pipe and 3,200 m for overhaul work, so the intended job decides which rating applies.

Always ask the supplier how a depth figure is measured. Some ratings refer to the maximum depth reachable under ideal string conditions, while others are working depths with normal tool strings. The same model may be quoted with several depth figures for different tubular sizes, as the 450HP XJ450 shows with 5,500 m for 73mm tubing and 4,500 m for 73mm drill pipe. When your programme is close to a rating, choose one model higher and confirm the calculation basis in writing. Where a programme mixes shallow drilling with workover, the boundary is set by the circulating and drilling duty rather than the mast height; the workover rig vs. drilling rig comparison explains where each class applies.

Step 2: Check hook load against the heaviest string.

Hook load is the second filter. The nominal hook load is the load the rig is designed to handle in normal service; the maximum hook load is the structural ceiling and should stay as reserve. A practical rule is to keep the heaviest string you plan to pull below the nominal figure and treat the maximum as the emergency and short-duration limit.

For a well with a 400 kN expected string, a 250HP XJ250 at 400 kN nominal leaves almost no margin; the 350HP XJ350 at 650 kN nominal gives a 60% margin for the same job. That margin matters for stuck-pipe handling, jarring and heavy completion loads.

The travelling system and the drill line work together with the drawworks to produce that load rating. In the ZYT range, the 450HP and 550HP units use a 4×5 arrangement with 26 mm and 29 mm line, the 650HP unit also uses 4×5 with 29 mm (1 1/8") line, and the 750HP and 850HP units step up to a 5×6 arrangement with 32 mm line. More effective lines raise the hook load for a given fast-line pull but reduce block speed, so a heavier rope arrangement is not automatically better for every programme. A well that needs frequent fast tripping is served differently from a well that needs one very heavy pull.

Step 3: Match mast height and hoisting speed to the work.

Mast clearance controls the stand length and the maximum tool or tubular section the rig can handle. In the ZYT range the mast rises from 18 m on the 150HP unit to 39 m on the 850HP unit. A 21 m or 23.5 m mast (XJ250, XJ350) suits standard workover stands; the 32-39 m masts on the 450HP and larger units suit longer stands and deeper wells. Hoisting speed follows the drawworks and rope arrangement: the XJ250 reaches 1.5 m/s maximum hook speed, while the heavier XJ350 is rated 1.1 m/s, a deliberate trade of speed for load capacity.

Step 4: Compare chassis, transport and site access.

A truck-mounted rig is only as useful as its ability to reach the well. Check the drive configuration, moving dimensions and weight against your road and site conditions. The moving dimensions in the ZYT range vary from about 10.6 m long and 22.8 t (150HP) to about 13.9 m and 31.5 t (XJ250, XJ350). The drive configuration steps up with the model: the 150HP unit runs on a 6×4 second-class chassis, the 350HP XJ350 moves to a 10×8 self-propelled chassis, and the 450HP and above units use 12×8 all-terrain chassis, which need wider turning space and stronger road ratings. For desert, jungle or mountain leases, confirm the axle configuration, tyre specification and the loaded height including the mast with the supplier before quotation. If the rig must relocate between wells every few weeks, count the rig-up and rig-down time and the permit weight into the operating cost, not only the purchase price.

Step 5: Include the supporting equipment in the scope.

Most workover programmes involve more than the rig. Coiled tubing, wireline, swabbing, well flushing, paraffin removal and fluid handling units are often deployed alongside. If your programme includes them, list the units in the same inquiry so the supplier can match the rig with the supporting equipment as one package, including manifolds, tanks and controls.

Step 6: Confirm the certification and the field environment.

The same model can be delivered with different compliance and protection levels. In the ZYT range, the XJ250 and XJ350 workover rigs are built to API 4F, while the XJ450, XJ550, XJ650 and larger units are manufactured to API 4F and API 7K. Confirm which standard applies to the exact configuration you order, because API 7K covers the power transmission components and API 4F covers the structure, and buyers who need specific certificates should state that in the inquiry.

Field environment changes what should be specified. For desert leases, confirm dust sealing, sand erosion protection and high-temperature cooling capacity. For plateau or cold-region operation, ask about cold-start preparation and low-temperature hydraulic and lubricating oils. For coastal or offshore-adjacent sites, corrosion treatment and paint specification become part of the scope. These items are configurable on most rigs, but only if they are requested before quotation.

Model quick reference: 150-850HP truck-mounted workover rigs

Prepare the inquiry data before contacting a supplier.

A specific inquiry produces a specific quotation. Include the following, with numbers where possible:

• Target depth and the tubing or drill pipe size you will run.
• Heaviest string weight or the hook load you expect to handle.
• Well count and relocation frequency between sites.
• Road width, bridge rating and site access conditions.
• Supporting scope: coiled tubing, wireline, swabbing, flushing, paraffin removal or fluid units.
• Quantity, destination port, expected delivery window and required documentation.

What to check when comparing suppliers.

Two suppliers can quote the same model name with different configurations. Ask how the depth and hook load figures are measured, whether the chassis and engine are standard or optional, which auxiliary systems are included in the package price, and how the rig is commissioned on site. Confirm the operating temperature range and the dust and corrosion treatment if the unit will work in desert, coastal or high-altitude conditions. Keep the final decision on the documented parameters, not on the marketing description. For budget-limited programmes, compare the new-unit quote against the condition and remaining service life of used equipment before committing; the new vs. used workover rig review sets out the inspection points for used units.