It’s all in the Plumbing: Rig Pumps, Manifolds and Standpipe

It’s all in the Plumbing: Rig Pumps, Manifolds and Standpipe

Insight by Mark May

December 2, 2013
 

One aspect of drilling rig operations that may be overlooked during on the job training (OJT) is a working knowledge of a rig’s “plumbing,” despite its vital role during an MWD job. Just as wireline logging relies on electric wireline to raise the tool string from the wellbore and to serve as a real-time communications link to the surface, MWD relies on rig pumps, manifolds, and standpipe and their associated plumbing to deliver communications to the surface.

MWD Field Engineers and Coordinators need to understand how each rig is plumbed, in order to avoid unnecessary trips to change a working MWD tool. This valuable information can be gained from collaborating with the Drilling Contractor personnel (Toolpusher and Derrickhand).

One of the least understood and least maintained pieces of equipment on the rig site is the Pulsation Dampener. The Pulsation Dampener (see image below) is the red sphere attached to the Rig Pump. The Pulsation Dampener is used to dampen pressure surges (or water hammer effect), when a piston pushes through a volume of mud.

F-1000-Mud-Pump-36

A cut-away of a Pulsation Dampener (see image below) shows the red upper section of the sphere, which is a rubber bladder filled with Nitrogen. The lower section, in black, sees the active discharge side of the mud pump and is filled with drilling fluids. With each stroke of the pump, the red bladder deforms to absorb the pressure surge.  Between each piston stroke the charged bladder will return the surge.

pulsation_dampener_hydril_type_k

The MWD Engineer should clearly communicate with the drilling contractor to ensure that the Pulsation Dampener is in working order; meaning:

  1. The Rubber Bladder is not broken so that it can hold and maintain the pre-charge of Nitrogen
  2. A gauge is installed to measure the amount of pre-charge
  3. The optimal pre-charge pressure is 1/3rd of the Operating Pressure seen on the standpipe, i.e., if the Standpipe Pressure is 3,000 psi, then the Pulsation Dampener pre-charge should be 1,000 psi.

When the Nitrogen Bladder is broken, the Pulsation Dampener cannot attenuate each pump stroke. This breakdown may lead to spurious noise that is not filtered by the surface computer, causing decode errors in the MWD surface gear. The same condition exists when the pre-charge of the Nitrogen Bladder is greater than the Operating Pressure, as the bladder will not deform on each pump stroke.  In either case, all of the components in the rig’s pumping system are stressed by the water hammer effect, which can lead to premature failures of the rig equipment.

Another phenomena that properly maintained Pulsation Dampeners can address is the attenuation of MWD pulse reflections. These reflections can appear at 4,000′ intervals, because MWD pulses travel at 4,000 ft./ sec., which is the speed of sound in fluids. At 4,000′ and multiples (8,000′, 12,000′, etc.), reflections may appear and can only be attenuated by changing something in the plumbing.

To attenuate reflections, the MWD field engineer should be prepared to request changes in the rig’s plumbing. One scenario calls for taking the second pump offline, if two pumps are being used, and to use only one pump for the survey after isolating the second pump with the manifold.  Conversely, if one pump is being used to drill, then the field engineer should be prepared to request that the second pump be brought online by opening the manifold. The second pump need not be active—only that the pulsation dampener of the second pump be exposed to the active “high” side of the system.

A better understanding of the rigs plumbing may help the field engineer avoid an unnecessary trip out of the hole to change the MWD—and in retrospect, may also assist shop personnel in solving some of the ‘No Problem Found’ failures.