Static filtration drilling fluids

Static Filtration. The static fluid loss of drilling fluids is a property that is regularly measured, both at the rig site during drilling operations... 

Figure 33 shows the time dependence of the volume of static filtrate collected from a typical water-based drilling fluid. The initial volume collected at time f = 0 is termed the spurt loss and represents the uncontrolled flow of filtrate and fine solids into the filter medium the spurt loss continues until a filter cake forms on the surface of the filter medium. 

Figure 33. Time dependence of the cumulative filtrate volume from the static filtration of a bentonite-polymer drilling fluid.

Dynamic Filtration. Dynamic (or cross-flow) filtration is a considerably more complex separation process than static filtration as the rate of filtration is a strong function of the flow of the drilling fluid. A number of studies (see reference 128 and the references cited therein) have demonstrated the various factors that control dynamic filtration rates. 

Effect of Composition on Fluid Loss. There have been many studies and tests of the effects of various additives (usually polymeric) on the static fluid loss of drilling fluids. There have been many fewer studies on the effect of these additives on dynamic filtration rates and very few that compare their effect on both dynamic and static rates. 

Plank and Gossen (144) have reported on the temperature dependence of API static filtrate volumes of simple drilling fluids using various polymeric additives. Figure 50 shows the dependence of filtrate volume on temperatures for a base bentonite fluid and with added starch, polyanionic cellulose, and a synthetic sulphonated polymer (39). Starch is an effective fluid loss additive up to about 100 °C whereas the polyanionic cellulose begins to lose its effectiveness at about 140 °C these... 

Figure 48. Comparison of rates offiltration of an invert emulsion oil-based drilling fluid under static and various dynamic conditions. 1. vm = 0 (extrapolated static filtration rate) 2. vm = 0.6 m/s 3. vm = 1.5 m/s 4. vm = 2.9 m/s. (Reproduced with permission from reference 142. Copyright 1954 American Institute of Mechanical Engineers.)...

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