Microbial activity evaluation and aerobic transformation of deep water offshore synthetic drilling fluids in soil: A case study of ternary mixture of synthetic ethyl esters of plants oil (Seep mixture) synthetic drilling fluid in agbami (Niger delta) deep water field

Abstract

Approval for offshore discharge of cuttings drilled with synthetic-based drilling Fluids (SBFs) by environmental regulatory and protection agencies usually require detailed laboratory biodegradation analysis of the base fluid chemicals among others. This concept of using biodegradation test as an environmental fluid-compliance criterion is that a fluid that degrades readily in the laboratory will not persist for an extensive period of time in the offshore environment.Hence, this research focuses on microbial activity measurement and aerobic biodegradation of a newly developed synthetic ester fluid named “ternary mixture of synthetic ethyl esters of plants oil (SEEPmixture)” and its’ comparison with already existing synthetic deep water fluids (SHBF and SEBF) in Agbami deep water field. The chemical composition and components of each drilling fluid sample was analyzed by a GC system combined with a high resolution accurate mass (HRAM) spectrometer while a Fourier transform infra-red (FTIR) spectroscopy was used for functional group identification.The microbial activity of each soil sample that was contaminated with different base oils (drilling fluids) and that of the uncontaminated soil sample (control) was determined by trapping the carbon IV Oxide (CO2) evolved from each soil sample with a strong alkali solution of barium hydroxide (Ba(OH)2) as the microbial biomass actively decompose soil organic matter. The degradation of the drilling fluid chemicals was monitored under aerobic conditions.The soil contaminated with SEBF fluid chemical experienced a low microbial activity due to its low respiration (low amount of evolved carbon IV oxide per mg of soil) but a more pronounced adverse effect on microbial activity was experienced by soil contaminated with SHBF chemical. While microbial activities were not impaired with the SEEP mixture fluid chemical presence in the soil. Meanwhile, in regards to soil aerobic transformation, the SEEP mixture fluid took the shortest time of 13.6 days for it to decompose to half of its original concentration (5mg/kgsoil) from an initial concentration of 10 mg/kg soil. This implies that the fluid sample is readily and inherently biodegradable in soil. Whereas, the SHBF fluid sample required about 34.50 days for it to decompose to half of its original concentration. This indicates its non-readily biodegradable nature in soil. The half-life of the SEBF was 25 days and thus not readily biodegradable.