Continuous Improvement in Slop Mud Treatment Technology

摘要

Oil-based drilling fluids can become contaminated with significant quantities of water as a result of low efficiency well bore displacements to water or brine and from operations such as rig and pit cleaning. The presence of excess emulsifiers and oil-wet solids in typical oil-based drilling fluids allows large quantities of water to be emulsified. These oil-continuous emulsions are often termed slop muds. This paper presents analytical data on the effects of water contamination on oil-based mud, the resultant slop-mud structure, the influence of shear, and quantification of the critical factors controlling phase-separation and chemical dose. Data will be presented showing the principles of continuous slop-mud treatment both on the laboratory and full-scale defining the important process parameters such as mixing energy, phase recovery rate, recovered drilling fluid properties, and treated water properties. Development of an understanding of the slop mud stream enabled a novel continuous treatment system to be built which provides efficient and fast phase-separation with recovery of the valuable drilling fluid phase, with significant advantages over current batch-type systems. The process requires in-line injection and mixing of surfactant into the slop mud, then continuous separation of the waste into water and drilling fluid using a gravity separator. The drilling fluid remains as a water-in-oil emulsion containing solids and other chemical additives, which can be reconditioned to acceptable properties for re-use. The water recovery rates are typically 70 to 90 vol% of the total water present in the slop mud. This recovered water is treated using centrifugation, filtration or other water-treatment techniques to meet or exceed discharge consent limits of 15 mg/L total petroleum hydrocarbon. Water collected in the rig deck-drain system which may also be contaminated with oil or oil-based mud can also be treated in the same manner as the recovered slop water. Because the process allows continuous treatment of the slop mud stream, the resultant equipment has significant benefits over the current batch-type systems including higher throughput and decreased footprint.