Analysis of heavy metal accumulation and environmental indicators in fluids and drilling cuttings

Abstract

Heavy metal pollution caused by oil well drilling operations is one of the environmental problems that the oil industry imposes on the environment. The source of such pollution should first be determined precisely to manage and control it. Studies show that the main source of environmental pollution in well drilling operations is the drilling fluid additives or the elements in the well column formations. In this research, in addition to measuring the concentration of heavy metals and comparing it with the existing standards, an attempt is made to determine the exact origin of these metals. To study the source of such pollution in the area of the Abteymour oil field in the southwest of Iran, 19 cuttings (from 8 formations), 10 waste samples (drilling mud and cutting), and 7 drilling muds and their additive samples from one of the wells were assessed to determine the concentration of heavy metals. In this study, a total of 56 elements were measured using the ICP-MS analysis method; however, 16 elements that had a higher concentration than the average of the upper crust (as a reference concentration) with Ni, Cr, and V elements were studied. These 16 elements included Fe, Ag, As, Ba, Bi, Cd, Cu, Mg, Mn, Mo, Pb, Sb, Sr, and W heavy metals, and Ca and S elements. The analysis of the examined elements' concentrations in muds and their additives revealed that samples of heavy water-based muds and barite contained the highest concentrations of the elements. The cuttings samples primarily had a higher concentration than the waste samples, which was due to the mixing of the cuttings of different depths in the waste and the dilution of the element concentration in the waste samples, according to an analysis of the variation of 19 elements compared to the depth. Among the studied formations, the Gachsaran Evaporite Formation has high concentrations of studied elements. This problem is due to the complexity of the lithology of Gachsaran Formation, which consists of all kinds of rocks such as anhydrite, gypsum, salt and marl. This result shows the importance of managing drilling operations in this formation to prevent the release of heavy metals in the environment. Based on the Igeo, Ca, Ag, As, Ba, Bi, Cd, Cu, S, Sb, and Sr elements had high levels of pollution in all samples of waste and drilling cuttings. Based on the EF, only Cr, Mn, and V elements had no enrichment, and other elements had different enrichment levels in waste and drilling cuttings samples. The main result of this study shows that the main source of heavy metal pollution in the first stage is the type of elements in the lithology of the well column formations and in the next stage is the type and additives of the drilling fluid used in the well. Specifically, in the Abteymour oil field, the main reason for the contamination of the Gachsaran formation is due to the complexity of the lithology and the use of heavy water base drilling mud. The results of this research show that before choosing the type of drilling fluid, it is necessary to do a detailed environmental study and identify heavy elements in subsurface formations and the designed drilling fluid.