Primary solids removal of centrifuge dewatering
The effect of early removal of solids from the drilling mud before its dewatering was investigated in the two-stage centrifuging tests. In the first-stage tests (size classification), the drilling mud was processed through the decanter centrifuge with no chemical conditioning (or with only pH adjustment by ferric sulfate).
In spite of the initial solids concentration and type of centrifuge, the solids content after the classification run was from 7.7 to 8.9% and the density stabilized at 8.55 to 8.8 Ibm/gal [1025 to 1054 kg/m3]. Additional classification runs did not make any difference. After the classification run, however, there was a substantial reduction in the flocculant dosage required to obtain jar-test floc
culation (taking 30% less polymer to reach a flocculation point).
Also, the cake-solids content from the classification run was much higher (66 to 70 wt%) than that from centrifuging with chemical conditioning (40 to 45 wt%).
The coagulation before centrifuging did not prove advantageous either III cake dryness or in separation efficiency. Both types of classification runs with and without coagulation did not really remove active colloidal solids from the drilling mud, as evidenced by the methylene blue test.
Altogether, the effect of preclassification proved very advantageous when followed by centrifugal dewatering with flocculation. Not only was flocculant dosage 30% smaller, but an increase (90 gal/min [0.34 m3/min]) of the maximum centrifuge throughput also was observed.