Application of Microtox Biological Toxicity Testing Technique in Drilling Fluid Analysis

This paper introduces the testing instrumentation, principles and testing method of Microtox, a biological toxicity testing technique. The EC₅₀ values of some mud additives and drilling fluid formulations were tested using the Vibrio fischeri as the testing bacteria. An onsite fast testing method was presented using Microtox technique. Laboratory experiments showed that drilling starch, XC, polyhydric alcohols, as well as natural high molecular weight polymers are nontoxic. Sulfonated phenolic, lignite, asphaltene, FCLS and the so-called tri-sulfonates drilling fluids have EC₅₀ values that are far less than the national standard of 30,000 mg/L. AMPS copolymers and synthesized high temperature polymer drilling fluids are nontoxic. Microtox technique provides two toxicity test methods for discharged drilling fluid in offshore drilling, a qualitative method and a quantitative method. Meanwhile this method can be used as a means of evaluating environmentally friendly drilling fluid.