In the pursuit of efficient and adaptable drilling solutions for challenging terrains, our engineering team embarked on the development of a specialized drilling rig. The primary objective was to create a system capable of operating in densely populated areas, farmlands, and regions with surface structures, where accessing shallow hydrocarbon reserves requires precise and minimally invasive techniques. This led to the conception and realization of the ZJ40CDY inclined well drilling rig, a machine whose core functionality is fundamentally enabled by robust rack and pinion gear mechanisms. The rack and pinion gear system is not merely a component but the central drive and guidance architecture, distinguishing this rig from conventional drawworks-based systems. The heart of this rig’s drilling operation is the DQ250Y hydraulic top drive, a unit we designed from the ground up to integrate seamlessly with the unique push-pull dynamics of a rack and pinion gear drive.
The global industry has seen pioneering work in inclined and rack and pinion gear-based rigs, primarily from North American and European manufacturers. These rigs are celebrated for their modularity, compact footprint, and high degree of automation. However, to foster domestic capability and offer a tailored solution, we initiated this project. Our design philosophy centered on creating a top drive that could directly meet the “push-while-drilling” requirement inherent to rack and pinion gear systems, where drill pressure is actively applied via the rig’s thrust rather than relying solely on drill collar weight. This report details our first-person perspective on the technical analysis, key innovations, testing protocols, and successful validation of the DQ250Y hydraulic top drive system.
Technical Architecture of the ZJ40CDY Rack and Pinion Gear Drilling System
The ZJ40CDY rig employs a portal-style derrick structure, a deliberate choice to align the top drive’s centerline with the derrick center. This alignment is crucial as it prevents the derrick from experiencing parasitic bending moments during drilling operations. The rig’s motion and force transmission are entirely governed by the interaction between multiple pinion gears and longitudinal racks. The structural composition is summarized below:
| Component | Function | Interaction with Rack and Pinion Gear |
|---|---|---|
| Derrick & Base | Provides structural support; angle adjustable from 60° to 90°. | Racks are mounted on the inner left and right sides of the derrick legs. |
| Push-Pull System | Generates axial force for hoisting, lowering, and applying drill pressure. | Incorporates hydraulic motors that drive pinion gears. These pinions engage with the fixed racks to move the entire system. |
| DQ250Y Hydraulic Top Drive | Provides rotational torque and speed for drilling, and handles pipe. | Connected to the Push-Pull System. The reaction torque from drilling is absorbed by the racks, which also act as guiding rails. |
| Racks | Serve as the linear gear and guiding track. | The fundamental rack and pinion gear element. Engages with pinions on the push-pull system for motion and with the top drive’s guide wheels for alignment and torque reaction. |
The rack and pinion gear pair is the definitive feature. The kinematic relationship for the linear velocity (v) of the top drive is given by the engagement between the pinion and the rack:
$$ v = \omega_p \times r_p $$
where $\omega_p$ is the angular velocity of the pinion gear and $r_p$ is its pitch circle radius. The force (F) generated for pushing or pulling is a function of the torque ($\tau_m$) from the hydraulic motors and the geometry of the rack and pinion gear:
$$ F = \frac{\tau_m \times N}{r_p} $$
where $N$ is the number of active pinion drives. This direct force translation eliminates the need for a conventional drawworks and block-and-tackle system.
Design and Specifications of the DQ250Y Hydraulic Top Drive
Our design for the DQ250Y top drive prioritized simplicity, reliability, and direct compatibility with the rack and pinion gear rig’s philosophy. The unit is a self-contained system comprising several integrated subsystems.
Structural Configuration: The main assemblies include the traveling block (which interfaces with the rig’s push-pull system), the power transmission system, a disc brake system, a tilting elevator link system with its innovative support arm, an integrated pipe handler (spinner and torque wrench), a gooseneck and washpipe assembly, a hydraulic power unit, and an internal blowout preventer (IBOP). A key addition is the buffer sub, installed between the IBOP and the drill pipe protector sub. This sub incorporates an anti-jump bearing to accommodate the compressive loads (“push” forces) delivered by the rack and pinion gear drive system, a load case not typically encountered by conventional top drives.
Core Technical Parameters: The top drive was engineered to meet the demands of drilling to 4,000 meters nominal depth in an inclined configuration. Its performance envelope is captured in the following table:
| Parameter | Specification | Notes |
|---|---|---|
| Max. Static Hook Load | 2,250 kN | Measured via load-sensing connection pins. |
| Rated Speed Range | 0 – 180 rpm | Two-speed range via motor displacement shift. |
| Continuous Output Torque | 30 kN·m (Low Range) | At full motor displacement. |
| Maximum Make/Break Torque | 45 kN·m | For connection services. |
| Peak Output Power | 283 kW | Constant power control regime. |
| Main Motor Hydraulic Pressure | 35 MPa (Rated) | Closed-loop circuit. |
| Main Motor Hydraulic Flow | 800 L/min (Rated) |
The power transmission is notably simple. We employed a low-speed, high-torque hydraulic motor with a hollow shaft. This motor connects directly to the main quill via splines, thereby transmitting torque without any intermediate gearbox. This direct drive approach eliminates the need for a gear reducer and its associated oil lubrication and cooling system, simplifying maintenance. All primary bearings are grease-lubricated, with inspection windows and temperature sensors for condition monitoring. The relationship between motor torque ($\tau_{motor}$), system pressure differential ($\Delta P$), and motor displacement ($D_m$) is fundamental:
$$ \tau_{motor} = \frac{D_m \times \Delta P}{2\pi} $$
The motor’s displacement can be switched, giving two distinct operational ranges that define the top drive’s speed-torque characteristic, governed by constant power control:
$$ P_{output} = \tau_{output} \times \omega_{output} \approx \text{constant} = 283 \text{ kW} $$
This results in a hyperbolic curve where torque is inversely proportional to speed within each displacement range.
Hydraulic Control System and Key Innovations
The hydraulic system is bifurcated into two primary circuits: the main drive closed-loop circuit and the open-loop pipe handling circuit. This separation ensures dedicated and optimized control for each function.
Main Drive Closed-Loop Control: This system features a variable displacement axial piston pump in a closed circuit with the hollow-shaft motor. The control valve manifold manages functions like motor displacement shifting, torque control, anti-torque release (for freeing stuck pipe), and case drain flushing. Speed and torque control are implemented via Proportional-Integral-Derivative (PID) closed-loop algorithms. The control system reads feedback signals for quill speed and motor pressure differential to modulate the pump’s swashplate angle. The torque limiting function, crucial for safe drilling and connection make-up, is exceptionally precise. The setpoint torque ($\tau_{set}$) is compared to the calculated actual torque ($\tau_{act} = k \times \Delta P$), and the error signal adjusts the pump command to maintain torque within a tight tolerance band, typically ±5% of the setpoint. This precision prevents damaging torque spikes that could harm the drill string or the rack and pinion gear engagement surfaces.
Pipe Handling Open-Loop System: A separate piston pump supplies pressure to an integrated valve stack that controls all auxiliary functions: the balancing cylinders, the disc brakes, the tilting elevator mechanism, the torque wrench (back-up tool), and the automatic IBOP. This modular approach simplifies troubleshooting and maintenance.
Pivotal Innovations:
- Direct Hollow-Shaft Motor Drive: By avoiding a gearbox, we reduced the number of moving parts, lowered potential failure points, and created a more compact and efficient power train perfectly suited for the reactive forces within a rack and pinion gear system.
- Tilting Elevator Link with Safety Support Arm: For inclined drilling, gravity acts to pull the elevator links away from the well center. While a hydraulic cylinder with a counterbalance valve traditionally controls the tilt, a potential valve failure could lead to uncontrolled swing. Our solution was to add a passive mechanical safety device—a spring-damped support arm. When the links are centered, they rest against this arm. If hydraulic control is lost, the arm physically prevents the links from swinging back, ensuring rig safety. This is a critical safeguard for operations on a sloping rack and pinion gear derrick.
- Integrated Load-Sensing Connection Pins: The pins that connect the top drive to the push-pull system are instrumented with strain gauges. They not only bear the entire weight of the top drive and drill string but also provide real-time, high-accuracy (within 1%) weight-on-hook data, which is essential for managing the push-pull forces of the rack and pinion gear drive.
- “Freewheel” Function for Maintenance: A simple valve arrangement allows the main motor’s inlet and outlet ports to be connected manually. This “freewheels” the motor, enabling the quill to be rotated manually with a chain wrench for maintenance without disconnecting any hydraulic lines, a feature we call the “empty disc motor” function.
- Open-Face Torque Wrench: The back-up tool features a swing-open design, allowing for rapid and easy replacement of jaws and inserts without extensive disassembly, enhancing operational efficiency.
Comprehensive Testing and Performance Validation
Following assembly, the DQ250Y top drive underwent a rigorous series of factory acceptance tests to verify every performance metric against our design specifications. The successful outcome of these tests confirmed its readiness for field deployment on the rack and pinion gear rig.
| Test Category | Test Method & Parameters | Results & Compliance |
|---|---|---|
| Structural Stress | Strain gauge measurement on critical weldments and components under design load. | All measured stresses were within allowable limits. No超标 items. Design validated. |
| Speed Range | Measured maximum quill speed in both displacement ranges (High/Low). | Low Range (Full displacement): 93 rpm (Target: 90 rpm). High Range (Half displacement): 182 rpm (Target: 180 rpm). Stable low speed achieved at 2 rpm without motor cogging. |
| Torque Output | Stall test: Quill locked, system pressurized to measure torque vs. pressure. | Low Range: 45 kN·m at ΔP = 33.1 MPa; 30 kN·m at ΔP = 22.2 MPa. High Range: 20.5 kN·m at ΔP = 30 MPa. Free-running torque ~280 N·m; breakaway torque ~600 N·m. All met specs. |
| Torque Limit Control | Set torque limits in drilling and make/break modes; measured actual output. | Precision control within ±5% of setpoint. The PID-controlled system effectively dampened hydraulic surges, providing smooth torque application essential for protecting the rack and pinion gear and drill string. |
| Make/Break Test | Using the integrated torque wrench on test drill pipe connections. | Make-up torque: 30.5 kN·m at 30.0 kN·m setpoint. Break-out torque: Successful at 41.0 kN·m. No slippage or damage to wrench jaws. |
| Load Pin Calibration | Applied known loads to the connection pins and read sensor output. | Combined measurement accuracy from the two pins was better than 1% of full scale. |
The torque limit control performance deserves special mention. The test curve demonstrated a rapid rise to the setpoint followed by a stable plateau, with minimal overshoot or oscillation. This is mathematically represented by the effectiveness of the PID controller in minimizing the error $e(t)$:
$$ e(t) = \tau_{set} – \tau_{act}(t) $$
The pump control signal $u(t)$ is calculated as:
$$ u(t) = K_p e(t) + K_i \int_0^t e(\tau) d\tau + K_d \frac{de(t)}{dt} $$
where $K_p$, $K_i$, and $K_d$ are the tuned proportional, integral, and derivative gains, respectively. The optimal tuning of these parameters was crucial for the dynamic response required in a rack and pinion gear drilling environment, where load changes can be abrupt.
Conclusion and Significance
The development and successful validation of the DQ250Y hydraulic top drive mark a significant milestone in our capability to provide advanced, specialized drilling equipment. This system was conceived and executed to fulfill the unique demands of an inclined well rack and pinion gear drilling rig. Its direct-drive hydraulic architecture, centered on a hollow-shaft motor, offers a simplified, robust, and maintainable solution. The innovative safety features, such as the elevator link support arm, directly address the specific hazards posed by non-vertical operations on a rack and pinion gear structure.
All performance tests confirmed that the top drive meets or exceeds its design specifications. It delivers precise speed and torque control, reliable pipe handling, and integrates seamlessly with the push-pull mechanics of the parent rig. The ability to accurately measure suspended load and handle compressive “push” forces makes it an integral component of the rack and pinion gear drilling paradigm.
In conclusion, the DQ250Y hydraulic top drive system is not merely an adaptation of existing technology but a purpose-built innovation. It effectively bridges the gap between conventional top drive functionality and the specialized needs of modern, compact, and highly automated drilling rigs that rely on rack and pinion gear technology for force transmission and guidance. Its successful development provides the industry with a new, reliable option for top drive configuration on special application drilling rigs, paving the way for more efficient and environmentally sensitive hydrocarbon extraction, particularly in complex and restrictive terrains. The lessons learned and technologies proven in this project, especially concerning direct drive integration and safety in inclined rack and pinion gear systems, will undoubtedly inform future advancements in drilling machinery design.