SOLID-PHASE TEST FOR COMPARISON OF DEGRADATION RATES OF SYNTHETIC MUDBASE FLUIDS USED IN THE OFFSHORE DRILLING INDUSTRY

A solid-phase degradation test has been developed to assess the fate i n marine sediment of synthetic mud base fluids used in the off-shore d rilling industry. The degradation rate of an ester-type drilling fluid was investigated at three nominal concentrations in a fine sand. A na turally occurring triester, olive oil, was used as a positive control and a traditional mineral oil served as an example of a poorly degrada ble substance. Two synthetic drilling fluids, an ester and a blend of n-alkanes with poly-alpha olefin and linear-alpha olefin, were compare d in a mud and a coarse sand to examine the effect of different sedime nts on degradability. Glass jars, containing marine sediment that had been homogeneously mixed with test fluid, were placed in troughs in a continuous flow of seawater. Periodically, triplicate jars were sacrif iced and, following solvent extraction, the concentration of test flui d remaining in the sediment was determined by gas chromatography with flame ionization detection. The test was able to reproducibly distingu ish between easily degradable and poorly degradable fluids. The rate o f degradation was concentration dependent; the half-life increased as the nominal concentration increased. The ester was more rapidly degrad ed man the blended synthetic drilling fluid and degradation was slower in sand compared with mud.