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.
Occupational hygiene requirements for operations on the Norwegian continental shelf when drilling with oil based drilling fluids, favour 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 concept using rotating separators as an alternative to shale shakers was developed to reduce this exposure. Drilling fluid with cuttings from the mud line is fed into a slowly rotating separator that forces the cuttings to move over a very large effective screen area with screens of selected sizes. The drilling fluid is efficiently removed from the cuttings since the area underneath the screen is slightly vacuumed. The improvements this treatment has on the occupational hygiene and the environmental impacts compared to use conventional shakers are illustrated. The current paper focuses on a field test where the rotating separator efficiency was compared with the efficiency of conventional shakers while drilling. The drilling operation was conducted with both water based and oil based drilling fluids. The field tests are described in detail. An efficient, but still gentle separation of drilled cuttings from the drilling fluid was observed. The paper discusses if the rotating separator managed to produce proper cuttings dryness even though 60–100% of the total cuttings load produced by the drilling rig was directed through the rotating separator. After completion of the field tests, the separator was brought onshore for further improvements. The flow capacity was increased with more than 100% based on these improvements. Introduction During the last decades, significant focus has been kept on improving the occupational hygiene aspects for offshore drilling operations. In Norway, this issue has forced the drilling industry to implement solids control equipment with good ventilation abilities in the shaker rooms on the rigs. Use of non-aromatic drilling fluid base oils with better hydrocarbon damp and mist properties have also been implemented.1,2 Still, even though ventilation hoods are used on the shakers, it is, in many cases difficult to comply with the requirement to keep the hydrocarbon damp and mist content below accepted levels.2 Norwegian drilling operation has to be performed in accordance with the NORSOK specifications.3 These specifications state the following: "Spaces containing shale shakers, drilling fluid tanks, vapours and drilling fluid/gas separators, shall similarly be equipped to prevent exposure to health hazardous gases and vapours." To optimise the occupational hygiene performance, it is necessary to minimize the generation of noise. The NORSOK specifications3 require: "All equipment with a noise level above 83 dBA (SPL) must be equipped with noise hoods or placed in separate machine rooms. Required noise insulation must not hamper the access to equipment for normal operation and maintenance (i.e. screen removal)." Other items affecting the occupational hygiene are the generation of vibration by the different equipments and the need to perform maintenance work on the equipments. Use of proper solids control equipment is essential to maintain the drilling fluid within its desired properties and to avoid generating unnecessary waste streams during drilling.4 Since the early 1930's the shale shaker has been the dominating device for primary solids removal.5 The optimum solids control design for a particular drilling fluid may not be generally valid for all fluid types.6 A specific combination of shaker and screens applicable for treating a particular water based drilling fluid may for instance not be suitable for treating oil based drilling fluids. Furthermore, the suitability of the screen and shaker combination may change during drilling because of changes in the drill cuttings morphology. Separation of solids with a particle diameter larger than 100 m can be achieved without problems on most shakers by the application of the correct screen size.7 Still, it is necessary to optimise the flow capacity for many shakers. Some improvements have been made to the shaker design and other improvements have been implemented by creating special shaker screens with high flow capacities.8 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 erode the cloth from the inside because of continuous vibrations, and the weight load from the drilling fluid acting on the cloth wires under tension and forces the wires to break.
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