Filter Press


Photograph by Frank Reeves, Sr.; Winkler County, Texas; 1942. University of Texas at Arlington Digital Library



OK boys and girls, what are these two hands in the pith helmets doing?


They're mud engineers and they are using a filter press to determine filtrate loss and wall "cake" thickness that the drilling mud is leaving behind as it is circulated downhole.

The filter press squeezes water out of the mud and the loss of fluid is measured in cubic centimeters of free water. Mud, or filter cake is left on a piece of filter paper and its thickness and consistency can be estimated.


Low water loss in the mud system prevents filtrate leak off that can damage a sensitive formation that is, for instance, high in shale (clay) content and when exposed to water can hydrate and swell. In some producing formations damaged by mud filtrate, permeability can be reduced. A good low water loss mud system for Gulf Coast clastic sands is 4-6 cc.


Wall cake is an essential part of well bore stability. In the photo above there are two pieces of filter paper with mud cake over them; this could be an oil based drilling mud or a fresh water system high in lignite that makes the wall cake black. The longer it takes to drill the well the more the well bore is exposed to the building of wall cake.


Tens of thousands of dollars can be spent on drilling mud systems that have good, strong wall cake and low fluid loss. Once the well is logged and otherwise evaluated, and before casing is run and cemented, tens of thousands of dollars need to be spent removing all this wall cake shit from the well bore to help ensure good cement to formation bonding.


Mud engineers often tend to a bunch of rigs at one time; they drive around from rig to rig analyzing mud properties and making recommendations on how the operator can doctor the mud...and spend more money. This mud shit is like owning a boat; it never ends. When the plug is bumped and the rig is being moved away, THEN you get to dispose of that stuff, as in throw away. THATS not cheap either.


Nothings cheap in the oil business. Its hard damn work. You never know from one day to the next what product prices will be, what costs will be, if you can find somebody to work for you, and whether, or rather when, Mother Nature is going to take big 'ol dump right on top of your head. Then there is always that Boggie Man sumbitch.


If you know someone who actually operates oil and gas wells with his or her own money, give them all the respect they deserve. They are smart, tough and tenacious. If you think its easy, try it for a while and write us a story about your experiences.