Making the upgrade is easier than operators may think.
by Rylan Ardoin (Southwest Oilfield Products)
November 11, 2014

In the drilling world, offshore technology is often at the forefront of innovation. Many advancements that are proven in offshore environments are eventually adopted by onshore rig operators. One offshore standard that is becoming more popular in onshore drilling is the 7,500-psi mud pump system.

Operator Needs & System Benefits

Several factors have prompted drillers to upgrade their mud systems, but one of the main drivers is the increased demand for directional and horizontal drilling. For decades, offshore rigs have operated and reaped the benefits of 7,500-psi mud pump systems. However, onshore rigs have relied on less robust 5,000-psi mud pump systems. The growing need for rig versatility has resulted in an in­creased number of land drilling rigs being converted to or built with 7,500-psi mud pump systems. Compared with lower pressure mud pump systems, 7,500-psi systems increase a rig’s drilling efficiency and depth range. With more feet drilled per hour, well completion times are drastically reduced, saving the contractor both time and money. Along with efficiency gains, higher-pressure capabilities also broaden the operating range of the mud pump system. The mud pump does not have to operate at full capacity for the duration of the drilling oper­ation, which results in reduced wear.

Triplex mud pumpFigure 1. Triplex mud pump. Article images and graphics courtesy of Southwest Oilfield Products

7,500 psi Conversion Summary

Upgrading to a 7,500-psi system is a relatively easy conversion, and many drillers coordinate these projects to take place while other scheduled maintenance is performed between drilling contracts. The mud system components that are replaced during the upgrade are located in the fluid end section of the mud pump. No modifications are made to the pump’s power end. The mud pump fluid end includes:

  • A suction and discharge manifold
  • Three suction modules
  • Three discharge modules
  • A discharge cross

During a 7,500-psi conversion, these key fluid end components are changed so that the mud pumping system can achieve and withstand the higher operating pressures safely.

Triplex mud pump fluid endFigure 2. Triplex mud pump fluid end

Higher pressure mud pump systems have drastically increased the efficiency of the well drilling process in conjunction with other advanced drilling technologies such as:

  • Pad drilling
  • Walking rigs
  • Alternating-current-powered rigs

New System’s Industry Effects

As a result, more footage has been drilled with fewer rigs in recent years, according to the most recent Drilling and Production Outlook published by Spears & Associates, Inc. In 2014, the industry is forecast to drill 45 million (12 percent) more feet with 46 fewer rigs than in 2012 (see Figure 3).

U.S. rig count and feet drilledFigure 3. U.S. rig count and feet drilled

The future projection of footage drilled versus rig count will continue to increase during 2015. Several oil and gas equipment manufacturers witnessed a significant shift to 7,500-psi mud pump systems during the past couple of years and expect the trend to continue and eventually become the new onshore industry standard.

Mud Pump Upgrade Myths

Because modifications are only made to the fluid end, many operators question whether a 7,500-psi fluid end will inflict additional loads on the mud pump’s power end. The most common concerns shared by operators relate to the power end’s rod load and liner reaction load and the overall weight difference of the fluid end.

Power End Rod Load

All mud pump power ends are rated with a maximum horsepower and rod load rating. The horsepower that a power end can handle is determined by its components, such as:

  • Connecting rod bearings
  • Wrist pin bearings
  • Crossheads
  • Main bearings and crosshead extension rods (pony rods)
  • Piston rods
  • Crankshaft and power frame

Considering these limitations, fluid ends are engineered to match a specific power end’s output. Rod load limitations are strictly observed to ensure operational integrity. Rod load is the force imposed on the piston rod during the forward and return stroke of the pump. Exceeding a pump’s rod load limitation can damage the piston rod and cause accelerated wear on power end components. As shown in Table 1, the rod load imposed on the power end remains stable for most piston sizes but will decrease in the higher pressure ranges. This decrease occurs because a smaller piston diameter is required to achieve the higher pressures.

Performance chartTable 1. Performance chart for power ends and fluid ends

Rod load forces actually decrease as the operating pressure increases. This eliminates the notion that high-pressure fluid ends add stress to the power-end during operation.

Liner Reaction Load

Operators are also often concerned about the liner reaction load. The liner reaction load is the tendency of the liner to push away from the wear plate during pumping. To eliminate this concern, the fluid end’s liner retention system has been engineered to retain the liner against the wear plate with enough force that the seal between the liner and wear plate is uncompromised regardless of the load. As indicated in Table 2, the liner reaction load has a direct relationship with the operating pressure. Failing to account for these forces would cause major issues for power end and fluid end components.

Liner reaction load chartTable 2. Liner reaction load chart for a 1,600-horsepower mud pump

To mitigate this concern, some fluid ends feature a liner retainer system that is fixed directly to the fluid end. This design eliminates the transfer of any liner reaction load to the power frame while securely holding the liner in place. Robust construction and stout fasteners help ensure that the operational integrity of this system and safety are maintained.

Fluid End Increased Weight

The additional weight imposed by a 7,500-psi fluid end is also a common concern for operators. The extra weight comes from the additional metal in the fluid end that, along with the L-shaped design, allows it to withstand the elevated pressures (see Image 1).

7,500-psi mud pump systemImage 1. Additional metal in the fluid end and the L-shaped design allow it to withstand the elevated pressures associated with the 7,500-psi mud pump system.

The weight difference between a valve-over-valve fluid end (see Image 2) and an L-shaped fluid end is relatively small.

Valve-over-valve fluid end moduleImage 2. Valve-over-valve fluid end module

In the example of a 1,600-horsepower pump, the net difference is approximately 1,000 pounds per cylinder, which is insignificant. Since most manufacturers offer an L-shaped fluid end as an upgrade option, most power ends are designed to handle the extra weight of this fluid end style without adverse effects.

Select Technology for the Future

Oil and gas exploration continues to be a technology-driven industry. Finding improved ways to produce the world’s natural resources has been a guiding principle in the drilling industry since the beginning and will become more important as the global demand for energy rises. The 7,500-psi mud system is one technological development that is changing the U.S. onshore drilling market. Conversion to this system is becoming important and is propelling the industry toward its goal of being safe, cost-efficient and environmentally friendly.