Bayesian spatial prediction of the area affected by drilling discharges from an exploratory well using water-based and non-aqueous-based fluids in Campos Basin, Brazil

Toxic drilling fluids and cutting discharges from oil and gas wells adversely affect local environment near the well site. To determine their effects on benthic communities, it is essential to know both the fate of the discharged materials and the chemical concentrations to which biota were exposed during and after drilling. This paper describes a mapping procedure using Bayesian spatial models to define the deposition area of drilling cuttings and fluids from an exploratory well in a deep-sea site in the Campus Basin, RJ, Brazil, taking into account the concentrations of barium and light hydrocarbons used as chemical tracers. The statistical procedures used allow comparisons between sampled sites and the prediction of results at unsampled sites, as well as the delineation of affected areas. The probable impact of the use of non-aqueous fluid (NAF) was measured through observed changes in sea-floor sediments by using Before–After Control-Impact comparisons in a study with three moments: one before drilling and two after drilling.