Comparison Between Acute and Chronic Toxicities of Drilling Fluids in Brazil: Is it Possible to Determine a Correlation Between Them?

Abstract

Establishing a regulation for the use and discharge of drilling and completion fluids in Brazil has been a challenge. The lack of specific procedures and limits for some of the environmental control parameters has been generating difficulties for the final approval of these fluids, requiring additional efforts and provoking discussions between the oil companies, suppliers and the Brazilian environmental authority.One of the most relevant control parameters required for the use and discharge of fluids in the environmental permitting processes is the evaluation of acute and chronic toxicity on marine organisms. Even though the limit required for acute toxicity using the mysid shrimp Mysidopsis juniae is well defined (96-hr LC 50 >30,000 ppm of SPP), there is not a limit established for the chronic toxicity using the larval stages of the sea-urchin Lytechinus variegatus, making the acute value the only established parameter used to define the approval of the fluids. Therefore, although chronic results are being generated for several fluid formulations, due to the lack of a specific limit, no direct use is being made of these results.The main purpose of this work is to contribute to the knowledge and proper use of toxicity results by comparing the values obtained for acute and chronic tests. For this evaluation, results obtained for different types of drilling and completion fluids will be used, both aqueous fluids (AF) and non-aqueous fluids (NAF). The results were analyzed by statistical tools to determine if a correlation between the two types of toxicity assays is feasible, considering the type of fluid evaluated.