Summary
Since the development of the drilling industry, the process for removing
drill solids from the drilling fluid has culminated in the use of shaker
screens as the primary or sole solution. It is, therefore, necessary to
optimize both filtration efficiency and the screen life to hinder drilled
solids from entering the drilling fluid. Optimum solids control can be obtained
by using knowledge of how damage to the filtration cloth arises, of how to
reduce it, and of how the particles in the circulation system influence the
general picture of the drilling process. When this knowledge is accepted,
established, and implemented in the drilling industry, it is possible to
maintain efficient drilling.
This paper describes, in detail, the theory and field examples on how wear
arises on the shaker-screen cloth. As will be shown, this knowledge has been
used to increase the solids-control efficiency and to reduce the screen wear by
more than 90% in several field cases where 17½-in. sections have been drilled
with oil-based mud. This has been achieved by use of a different screen
configuration, running with top screens with finer cut points than normal. This
leads to removal of 90 to 95% of the solids from the fluid using the top deck,
thereby minimizing the wear on the finer bottom-deck screens. The documentation
is based on practical offshore results from these drilling operations,
including data from the drilling log, laboratory analyses of the drilling
fluid, and of the particle-size distribution (PSD) of the drilling fluid. The
particular focus of this article is the application of double-deck shakers.
Introduction
Correct use of solids-control equipment is essential to maintain drilling
fluid within its desired properties and to avoid generation of unnecessary
waste streams during drilling (Bouse and Carrasquero 1992). Since the early
1930s, the shale shaker has been the dominant device for primary solids removal
(AADE 1999). Additional equipment such as desilters, desanders, and centrifuges
were often used in the past to maintain proper solids control. Although it is
dependent on the choice of correct shaker screens, most shakers at present
perform sufficiently to be able to act as the sole solids-control device
without the use of desanders and desilters.
The optimum solids-control design for a particular drilling fluid may not be
generally valid for all fluid types (Lal and Hoberock 1988). For example, a
combination of shaker and screens applicable for treating water-based drilling
fluids may not be suitable for treating oil-based drilling fluids. Furthermore,
the suitability of the screen and shaker combination may change during drilling
because the drill-cuttings morphology changes.
During the last few decades, major shaker-design improvements have been
made. The circular-motion shakers used up till the 1980s have been replaced by
elliptical-motion and linear-motion shakers. Furthermore, double-deck, or even
triple-deck, shakers have been implemented in the industry. Alternatives to
shakers have been tested to improve occupational hygiene aspects although this
type of equipment has not yet reached the market (Saasen et al. 2003).
Sinusoidal-formed screens have been implemented on some shakers to increase the
flow capacity (Neidhardt 1995).
Shaker operation has also been automated (Scott 2006). Scott (2006) claims
that use of this automated system leads to an increase in shaker-screen life.
However, Scott (2006) does not reveal the screen selection for this case.
Therefore, it is difficult to use this information in the present analysis.
Removal of solids with a particle diameter larger than 120 to 150 µm can be
achieved without problems on most shakers today by the application of the
correct screen size (Wollherr and Krobok 1998). There are many types of screens
on the market. The following analysis is general and does not compare any
products or designs.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
14 August 2006
- Meeting paper published:
13 November 2006
- Revised manuscript received:
29 May 2008
- Manuscript approved:
6 June 2008
- Version of record:
10 December 2008
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