Summary
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 a process for separating and recycling slop muds in a
continuous process. 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 will be presented. In addition, treatment of the slop-mud on a
continuous basis will be demonstrated 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 that 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 reuse. 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 that 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.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
26 July 2007
- Meeting paper published:
11 November 2007
- Revised manuscript received:
11 December 2008
- Manuscript approved:
12 December 2008
- Published online:
20 August 2009
- Version of record:
28 September 2009
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