Physico-Chemical Properties and Heavy Metals of Fresh and Spent Drilling Muds from a Selected Oilfield Environment

Abstract

This work evaluated the concentrations of heavy metals, total petroleum hydrocarbons (TPH) using AAS, GC-MS and UV-Vis spectrophotometer respectively, as well as physico-chemical parameters of freshly formulated, and the effluent samples of drilling muds from Eastern Obolo Oilfield in the Niger Delta of Nigeria, using appropriate standard methods. The samples consisted fresh Base mud, Base mud formulated with chemicals / additives but not used for drilling operation, Spent Oil-base mud (OBM) and Spent Water-base mud (WBM). GC-MS analysis for TPH indicated a range of n-alkanes with a higher concentration (46118.28 ug/l) in the OBM compared to WBM concentration (17185.95 ug/l). The analysis of TPH using GC-MS revealed a more comprehensive range of n-alkanes present in the OBM and WBM compared to the UV-Vis spectrophotometer. The TPH for OBM (67.0 mg/kg) was substantially higher compared with WBM (1.30 mg/kg), using UV-Vis spectrophotometer. In comparison, the results indicated a lower TPH of 1.00mg/kg for fresh mud not mixed with formulation chemicals. The TPH concentrations were found to be significantly higher in the OBM compared to fresh base mud and WBM.  In general, the results indicated a TPH trend thus: OBM > WBM > Base mud. The TPH obtained for OBM (67.0 mg/kg) was higher than 50mg/kg allowable for drilling mud in the environment.  Heavy metals analyses indicated variable concentrations and abundance in the drilling mud samples investigated, especially in manganese (Mn) ranging between (42.17mg/l – 76.65mg/l) in all the mud samples investigated. The physical properties (Density, Total Dissolved Solid (TDS), Viscosity and PH) evaluated showed variations in the different drilling muds, specifically between fresh base mud compared to mud already formulated with additives/chemicals. The results from this study are critical for stakeholders when considering drilling mud properties for optimal and efficient performance and also when choosing disposal of drilling mud effluents, especially in the study area where extensive oil/gas operation is currently ongoing.