Surface Application of Oil-Base Drilling Mud Mixed with Gypsum, Limestone, and Caliche

The current increase in oil and gas drilling activity has resulted in increased production of oil-base “mud” (OBM) in need of disposal. Land application of OBM to agricultural land is a common disposal technique that presents agronomic and environmental challenges since the material is rich in petroleum hydrocarbons. The objective of this study was to determine the effect of mixing OBM with bulking materials on hydrocarbon degradation and forage production after land application of the mixtures. An OBM was collected from Oklahoma and characterized for environmentally relevant properties such as total petroleum hydrocarbons (TPH) and trace metals. The OBM was bulked with either limestone, gypsum, or caliche, at a ratio of 3:1 or 1.5:1 bulking material/OBM. All mixtures were surface applied at equal TPH loading rates (8625 kg ha–¹) and soil samples taken at 7, 45, 60, and 170 d after application for evaluation of TPH, electrical conductivity (EC), pH, and sodium absorption ratio (SAR). After 7 d >50% of applied TPH degraded, which resulted in soil concentrations less than thresholds recommended for residential neighborhoods. By Day 170, 99% of applied TPH degraded. There was mostly no difference in TPH degradation as a function of type and amount of bulking agents used with OBM. Application of OBM did not significantly decrease forage yield compared to unamended control. Therefore, use of caliche, limestone, or gypsum bulked with OBM at a 1.5:1 ratio (bulking agent/OBM) would suffice for achieving acceptable TPH degradation when mixtures are surface applied and non-incorporated.