The purpose of filtration any fluid is to prevent the downhole contamination of the formation. Contamination reduces production and shortens the life a producing well. Contamination of the formation with particles can occur during wellbore clean up, perforating, fracturing, acidizing, workover, water injection, and gravel packing as well. Any time fluid is put into the well bore with a solid content, no matter how slight; there is a chance of damaging the formation.
The contamination from each well is never the same.
A fluid contaminant can come in many sizes and forms. Drilling operations produce cuttings,
rust, scale, pipe dope, paraffin, undissolved polymer, and other material on the casing or
pipe string. All these materials contribute to the amount of solids in the fluid.
Techniques for estimating solid content and fluid clarity are important. The gravimetric
method (centrifuge) for determining the quantity of nonbiological particles, and turbidity
measurements to estimate the total amount of undissolved solids are simple and the most reliable quantitative measurements being used today.
With the wide range of formations exposed to completion fluids, filtration services must
be tailored to each well. No two wells are ever exactly the same. The nature and
chemistry of the formation need to be characterized. Effective filtration service
requires a cooperative effort on the part of all those involved in drilling and production,
so that formation damage can be minimized.
In the past, operators have generally tried to have clean, solids-free fluids in the well bore
before perforating intervals. Porous and permeable rock acts like a deep bed filter for
suspended particles, and even a solids-free fluid may damage a formation if not
chemically compatible with the formation rock.
Filtration costs will be covered in time.
Filtration has evolved from old surface filtration systems with low flow volume to highly
sophisticated filtration systems. Although oilfield filtration can be expensive and time consuming, a case for filtration fluids can be made for every completed well and workover where the net production has been increased more than enough to pay for the difference.