A MUD PUMP that is two-thirds theweight and up to one-third smaller thana typical mud pump is being tested inNorway before a production model willbe installed on a rig in the field in 2003.

National Oilwells Hex Pump 150, a1,500 HP unit, has been under develop-ment for the past two years. The compa-ny also plans to offer a 2,400 HP versionas well.

The Hex Pump utilizes sixpistons/plungers arrangedvertically in a cylinder-shaped pump assembly.

A specially-profiled camrotates above thepistons/plungers to producethe pumping action withspecific timing to signifi-cantly minimize output pul-sation compared with tradi-tional pumps.

The cam operation is drivenby two AC motors and pro-duces a more constant pis-ton/plunger speed and flowrate, resulting in longer lifeof the valves and mechani-cal components, accordingto the company.

Due to the AC drive flexibil-ity, the pump can performboth high pressure or highflow operation withoutchanging the liner size.

In addition to the pump offeringincreased performance, efficiency andversatility due to its size and output, theunit also produces nearly zero pulsationcompared with a mud pump typicallyfound on rigs.

The pump mechanically has zero pul-sation, said Jason Whyte, New Prod-uct Implementation Manager for Nation-al Oilwell.

An advantage of zero pulsation relatesto downhole measurements. A lot oftools use measurement while drilling(MWD) that relies on mud pulse teleme-try to send signals back to the surface.

The tools produce a pulse in the mudthat travels up the mud column to thesurface.

Any pulsation created by mud pumpsacts as noise or interference on the puls-es being transmitted through the mudcolumn.

Because of the slight compressibility ofthe mud, we do get small pulses in theflow but we achieve about 92% less pul-sation compared with a Triplex pump.

That is achievable due to the mechani-

cal operation of the pump. There is asingle overhead cam that rotates as itoperates the cylinders in and outthrough the suction and discharge phas-es.

The way the phases are timed with eachother, it achieves zero pulsation.

The cams profile also helps result inzero pulsation. It is a specialized profilethat helps reduce pulsation. NationalOilwell has a patent pending on the cam.

The lighter weight and smaller size ofthe Hex Pump could enable rig upgradeswhere there is a fixed amount of spaceto install additional mud pumps.

Because the shape of the Hex Pump isround, Mr Whyte said, the space that

would normally be used for two Triplexpumps can accommodate three of thesepumps.

Theoretically it provides 50% morepumping capability in the same sizepump room.

While the final cost has yet to be deter-mined, it is anticipated it will bebetween 20%-25% more than a Triplex

pump, Mr Whyte noted.

This is partly due to moremachined parts in theHex Pump, according toMr Whyte.

There are about the samenumber of moving partsand mechanical compo-nents as a Triplex pumpbut the cam is speciallydesigned specifically forthe Hex Pump and is pro-duced at an outside facili-ty rather than at NationalOilwell.

There are also variousother specialized compo-nents, Mr Whyte noted.

The 1,500 HP version andthe still to come 2,400 HPversion will be the samesize physically.

The horsepower increasecomes from upgradessuch as larger capacity

A/C motors as well as some internalcomponents that will be upgraded forthe higher capacity. The pumps mainstructure will remain the same.

Other features of the Hex Pump include:

More consistent plunger speed

Reduced wear and maintenance

Cartridge style valve system for easiermaintenance

Lower peak flow rate through valves

Smaller fluid end components for eas-ier handling

AC motors to achieve either high pres-sure or high flow without changing linersize

34 D R I L L I N G C O N T R A C T O R September/October 2002

Smaller mud pump achieves near zero pulsation

National Oilwells new design Hex Pump is undergoing testing in Norway beforebeing installed on a rig in the field in 2003. The pump is two-thirds the weight andone-third smaller than a typical mud pump.