The present invention relates to high pressure, reciprocating pumps of the type typically used to circulate drilling fluid through a wellbore. More particularly, the present invention relates to a system and apparatus for coupling a piston rod to an extension rod that eliminates the need for heavy tools in the coupling and uncoupling of the rods. Still more particularly, the present invention relates to a system and apparatus that simplifies the maintenance of the pump while maintaining a reliable mechanical attachment between the piston rod and the extension rod.
In extracting hydrocarbons, such as oil and gas, from the earth it is common to drill a well into the earth formation containing the hydrocarbons. A drill bit is attached to a drill string, including joined sections of drill pipe, suspended from a drilling rig and extended into a wellbore. During drilling operations, drilling fluid, or mud, is pumped down through the drill pipe, into the hole through the drill bit, and back to the surface. Drilling mud is used to lubricate, cool, and clean the drill bit. The drilling mud also provides well control by counteracting formation pressure and returns cuttings from the drilling process to the surface.
Large reciprocating pumps, also known as positive displacement, slush, or mud pumps, are commonly used for pumping the drilling mud. Because of the need to pump the drilling mud through several thousand feet of drill pipe, such pumps typically operate at very high pressures. Moreover, a large volume of mud must be pumped so that the mud will emerge from the drill bit downhole at a relatively high velocity in order to lubricate and cool the bit and effectively remove cuttings from the hole. Lastly, the pressure generated by the mud pump contributes to maintaining a predetermined total downhole pressure, which is necessary to prevent well blowouts and optimize drilling performance.
Mud pumps are typically of a modular construction and comprise a power end and a fluid end. The power end provides the power for the pump from a power-producing device, such as a diesel engine or electric motor, and drives an output shaft or an extension rod. The fluid end of a mud pump comprises the equipment that actually interacts with the drilling mud, such as pistons and liners. Because drilling mud is highly abrasive, the fluid end is typically designed so that dynamic parts that are in contact with the mud can be replaced. These parts are often replaced as part of a regular maintenance schedule on set intervals, some components are replaced as often as every few weeks. The fluid end and the power end are connected between the output shaft and the piston, usually by an extension rod or other connecting component.
The pistons and cylinders used for such mud pumps are susceptible to a high degree of wear during use because the drilling mud is relatively dense and has a high proportion of suspended abrasive solids. As the cylinder becomes worm, the small annular space between the piston head and the cylinder wall increases substantially and sometimes irregularly. This decreases the efficiency of the pump. To reduce the effect of this wear, the cylinder typically is provided with a replaceable cylinder liner and piston. It is the usual practice to replace the cylinder liner and piston at end of their useful life, which is normally every 500 to 1500 operating hours, depending on pump design and operating conditions.
Although the pumps are not always operating, the typical drilling rig operates non-stop, therefore the replacement of worn pistons and cylinder liners needs to be performed on a regular basis. Furthermore, the replacement of these components needs to be accomplished quickly and easily. The first step in the maintenance of the mud pump is separating the fluid end from the power end by disconnecting the extension rod from the piston rod.
In U.S. Pat. No. 5,904,071, a hydraulically controlled piston rod assembly for use in high pressure reciprocating pumps is disclosed. The disclosed piston rod assembly comprises a connector releasably connected between a power end component and a fluid end component, with the connector having a body member and first and second tension links, wherein each link has a coupling pin to co-operate with respective apertures on the end components. The connector further includes biasing means for biasing the links, when coupled, in shear to resist uncoupling thereof and a means for causing movement of the one or more links against said bias to enable their movement into co-operative disposition with the end components to permit coupling or uncoupling. At least one of the links does not extend beyond the axial limit of the body. The assembly utilizes springs to bias the links and hold the pin in shear. The assembly uses a centrally located pressure area to push two pistons in opposite directions to counteract the biased springs so that the pins can be removed.
The above-disclosed assembly relies on springs to provide the biasing force to keep the pins from uncoupling. Over time, these springs will fatigue and provide less biasing force. The assembly also requires the use of specially designed end components adapted to accept the coupling pins.
Notwithstanding the above teachings, there remains a need for a system and apparatus for coupling and uncoupling the shafts in a high pressure reciprocating pump that overcomes the foregoing difficulties while providing more advantageous overall results.
The present invention features a system and apparatus for easy and reliable coupling and uncoupling of two cylindrical rods, such as the extension rod and piston rod of a mud pump. The apparatus utilizes a single hydraulically operated ram to provide a compressive force between the two rods. The apparatus also incorporates a mechanical lock to maintain the compressive force once pressure is removed from the ram. The mechanical lock provides a backup to the hydraulic ram and increases the reliability of the system. The apparatus allows the extension rod and the piston rod to be coupled and uncoupled without requiring wrenches, hammers, or impact tools. This creates a safer and more predictable process for coupling and uncoupling two rods, as well as decreasing the time required for the process.
The first rod is coupled to one end of a connector body by pins or some other connecting apparatus. The second rod fits inside of the body and face to face with the first rod. A hydraulic ram travels along the outside of the second rod and forms a differential pressure chamber by sealing against the inside of the body. The sidewall of the body has an opening that allows the application of pressure to the pressure chamber. The second rod has a groove that accepts a split ring that forms a circumferential shoulder on which the hydraulic ram bears. Application of pressure to the pressure chamber moves the ram against the split ring shoulder and imparts a compressive force between the ends of the two rods. The compressive force applied is adjustable but should be greater than the maximum tensile force that will be applied during operation of the pump. This results in a net compressive force for all operating conditions and significantly increases the fatigue life of the coupling mechanism.
After the desired amount of load is imparted to the cylindrical rods a threaded retainer screw is installed onto the body to hold the hydraulic ram in place once pressure is removed. The pressure application device can be removed during normal operation. To uncouple the rods, pressure is reapplied to the ram and the retainer screw is removed. Once the retainer screw is removed, one or both of the rods can be uncoupled, and maintenance of the pump can proceed.
The present invention provides an improved method and apparatus to couple and uncouple the extension rod and piston rod of a mud pump. Because no heavy tools are needed to couple or uncouple the rods, the task can be accomplished faster and more reliably. The inclusion of the retainer screw as a mechanical lock further increases the reliability of the system.
Thus, the present invention comprises a combination of features and advantages that enable it to overcome various problems of the prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description and referring to the accompanying drawings.