When mechanical separation equipment is used to remove suspended solids from liquids, capture determinations provide a simple means of evaluating its performance. Capture is defined as the fraction of incoming suspended solids that report to the discarded stream.
Weighted NAFs present a special problem because of the cost of the base fluid, which can exceed $200/bbl. The objections to series centrifugation raised in the previous section are equally valid for these fluids. Fortunately, NAFs are more solids tolerant than water-based fluids. However, when NAFs are used long enough, ultra-fines and colloids can accumulate to problem levels and force difficult choices.