Effect of non-aqueous drilling fluid and its synthetic base oil on soil health as indicated by its dehydrogenase activity

Drilling fluids are used for drilling natural gas, oil and water wells. These spill over into the surrounding soil at the point of drilling, which may impair soil health. A laboratory investigation was carried out to determine the effect of non aqueous drilling fluid (NADF) and synthetic base oil used with it on soil health as indicated by the dehydrogenase activity. A non-sterile sandy loam soil was treated with different amounts of NADF and base oil at a rate of 800, 8,000 and 16,000 mg kg⁻¹. Initially, reduction in dehydrogenase activity was observed, but it increased with the incubation time. On the 60th day of incubation dehydrogenase activity in untreated control was 1.04 mg TPF g⁻¹ h⁻¹ whereas in the soil samples treated with NADF and the base oil (16,000 mg kg⁻¹), the activity was 1.53 mg TPF h⁻¹ and 1.90 mg TPF h⁻¹, respectively, which was 72 and 82% more than in untreated control. Base oil-treated soil showed more dehydrogenase activity than that observed with NADF. Both NADF and base oil stimulated the soil dehydrogenase activity.