Optimized Performance by the Use of Rotating Separators as an Alternative to Shale Shakers

Abstract

Occupational hygiene requirements for operations on the Norwegian shelf when drilling with oil based drilling fluids favours the use of enclosed system for solids control. Personnel working with shale shakers are often exposed to a base oil mist and vapour at an unacceptable level. A principle with the use of rotating separators as an alternative to shale shakers was therefore developed. The paper describes the principle with rotating separators as an alternative to shale shakers in detail. The paper focuses on tests where the separator efficiency from the rotating separator is compared with the efficiency from conventional shakers. The separator principle is to feed the drilling fluid with cuttings from the mud line into a slowly rotating separator that forces the cuttings to move along a very long screen section with selected screen sizes. The drilling fluid is effectively removed from the cuttings since the area outside the screen is slightly vacuumed. This principle result in an apparatus with an effective solids separation being among the better separation results obtained by conventional shale shakers. The paper also describes the improvement on the occupational hygiene and the environmental impacts resulting from the use of the rotating separator compared to the current status from using conventional shakers. Norwegian drilling equipment standards require that the noise level from a device in the drilling area should be less than 83 dB. The paper describes how this requirement is satisfied and that the noise level is far below the requirement level when using the rotating separator. Introduction Use of solids control equipment is essential to maintain drilling fluid within its desired properties and to avoid generation of unnecessary waste streams during drilling1. Since the early 1930's the shale shaker has been the dominating device for primary solids removal2. Additional equipment like desilters, desanders and centrifuges were often used to maintain proper solids control. The optimum solids control design for a particular drilling fluid may not be generally valid for all fluid types3. A combination of shaker and screens applicable for treating a particular water based drilling fluid may for example 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. Separation of solids with a particle diameter larger than 100 m can be achieved without problems on most shakers today by the application of the correct screen size4. Still, it is necessary to optimise the flow capacity for many shakers. Some improvements have been performed on the shaker design and other improvements have been performed by creating special shaker screens to handle large flow capacity5. The life time of a fine mesh screen used on shale shakers is often limited since in addition to surface wear, entrapped particles within the screen cloth can erode the cloth from the inside because of continuos vibrations. In this respect there is a need for equipment that separates drilling fluids from cuttings more gently. A focus on occupational hygiene aspects when drilling with oil based drilling fluids has forced the drilling industry in Norway to use non-aromatic base oils with good hydrocarbon damp and mist properties6,7. Still, even though ventilation hoods are used on the shakers, it is, in many cases difficult to reach the requirement to keep the hydrocarbon damp and mist content below accepted levels8.