Compact Vacuum D-GASSER

Process overviewGases are entrained in drillingfluids from the wellbore duringnormal drilling operations aswell as during “kicks” or well-control situations. These gasespresent safety hazards and createoperational problems when gas-laden fluid reaches the surface.Degassing is accomplished at thesurface by one of two methods(1) atmospheric separation or(2) vacuum separation.

The simplest form of atmosphericdegassing occurs naturally in thesurface mud tank system. As themud flows over the shale shakersand through the pits, gas bubbleswill form in the mud and escape tothe atmosphere. In event of haz-ardous gases being present, it isdesirable to localize the point wheregas is released from the mud byinstalling a vacuum-style degasser.

Vacuum-style degassers areinstalled in the first compartment

downstream of the sand trapand upstream of any centrifugalpumps. Vacuum degassers workby removing entrained gases from

the drilling fluid by exposing thefluid to pressures well belowambient atmospheric pressure.

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P R E S S U R E C O N T R O L

Features and Benefits• Fiberglass leaves eliminate

corrosion; reduce repair andmaintenance costs

• Large Cleanout Port allowseasier access for cleaning insideof D-GASSER

• Greater surface area allowsgas-entrained mud to be releasedmore efficiently

• Interchangeability of manyof the parts as the HorizontalD-GASSER allows use of existinginventory parts

• Same field-proven vacuumpump as Horizontal D-GASSER

• Shorter footprint can be installedin smaller spaces

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How it worksThe M-I SWACO Compact D-GASSERunit works by removing entrainedgases from the drilling fluidas illustrated at right. Vacuumdegassing is more effective thanatmospheric degassing due to theexposure of the drilling fluid topressures well below ambientatmospheric pressure. The unitdirects the incoming fluid flow overinternal plates that create largesurface areas over which thin layersof the fluid continuously flow. Thetransit time required for the gas totravel up, through the fluid and“break out” of the mud is mini-mized by spreading the fluid intothin layers.

At pressures below atmosphericpressure, the rate at which gas sep-arates from a fluid is accelerated.The low pressure promotes thegrowth of large gas bubbles whichrise rapidly to the nearest surface.

The free gas that breaks out ofthe drilling fluid is continuouslyremoved from the vessel by theaction of the piston-style vacuumpump on the unit. The removedgas is typically directed to theflare stack.

The level of mud within the ves-sel is controlled by a float valve to

ensure that the disk stack is neversubmerged. As fluid level rises andlifts the float, air enters the vesselthrough the three-way valve todecrease the vacuum inside thevessel. With less vacuum insidethe vessel, the rate at which fluidis drawn into the tank slows andthe rate at which fluid exits the ves-sel increases. The fluid level insidethe vessel drops rapidly until the

float lowers and full vacuumis restored.

A liquid-trap tank in the gas-removal piping collects any fluidor condensate that may haveentered the gas-removal piping.A float ball in the liquid-traptank prevents the liquids fromentering the vacuum pump.

Incoming fluid disperses in thinlayers over the internal disk stack

Motive force fluidto venturi jet pump

Outlet to mud pit Inlet: gas cut mud

Fluid level

Gas outlet

Degassedmud