Landfarming of Drill Cuttings

Abstract

Abstract Over the last two years, experiments have been conducted on the biodegradability of oil-based mud drill cuttings by spreading the cuttings on farm land in France. The results of two years of tests on the soil's natural capacity to biodegrade hydrocarbons are very positive and the success of this experiment may be a good alternative solution for eliminating these drilling wastes which are at present disposed of in landfills after chemical or thermal treatment. Soil sampling was carried out on four plots, with an annual evaluation of the plants, roots and grain after harvesting. This is the first time that such an experiment has been run on a 7.5-acres land plot with adequate drainage networks to ensure an efficient monitoring program. The main objectives of these experiments were to show that drill cuttings spread on 'open fields' in suitable concentrations are not harmful, and to verify that this method has no impact on soil, surface and/or ground water and crops. The two years monitoring results show that:–the hydrocarbons are retained in the top soil to a depth of 8 inches,–when the spreading rate is lower than the soil retention capacity, there is practically no migration and leaching,–the hydrocarbons are biodegraded to over 75%,–the cuttings have no phytotoxic effects on the germination of the crops and the influence of the harvest yield was very low. No trace of petrogenic hydrocarbons have been detected in the grains of the successive crops. Introduction Exploration, production and refining of hydrocarbons generate waste which may contain hydrocarbons. In this case, waste is usually disposed of in authorized landfills, or incinerated, but may sometimes be treated biologically instead. Oil drilling operations generate 1 to 2 cubic meters of solid debris per meter of length drilled. These debris, called drill cuttings, are mostly composed of mineral substances found in the ground, mixed with drilling fluid which may contain hydrocarbons, water and various additives. Cuttings from a site that has been drilled with an oil-based mud may contain as much as 15% hydrocarbons. Much research has been conducted on landfarming of these oily cuttings, particularly on oily muds from refineries. The research involved spreading oily muds on farm land or on fallow industrial land. The doses applied were often so high that the hydrocarbon concentrations in the soil hindered the development of vegetation. On the other hand, hydrocarbon concentrations of less than 1 L/m2 will allow vegetation to sprout and grow. It is a well-known fact that hydrocarbons can be easily biodegraded by bacteria naturally present in soils, but the effects of mineral components and additives in drill cuttings have never been studied. However, it must also be noted that some hydrocarbon components are biodegradation-resistant. Many wells are drilled in rural areas, often far from special treatment facilities such as incineration plants. Extensive spreading of low concentrations of drill cuttings on farm land could be considered as an economical and environmentally friendly solution for biological treatment of hydrocarbons. It is in this context that experiments were conducted by spreading oil-based mud drill cuttings on open fields. Experimental methods Oil-based mud cuttings were sampled from a well drilled by TOTAL, on the Montmirail site in the Department of Marne, France. The drill cuttings were essentially composed of 83% mineral matter, 12% calcium (lime) and 12% organic matter, including hydrocarbons used in the drilling fluid. The heavy metal concentrations in the cuttings were well below levels authorized in France for spreading muds from urban waste-water treatment plants, and hence did not constitute a restriction to spreading. P. 31