Abstract

Since the development of the drilling industry the process has culminated in using shaker screens as the primary or only device for removing drill solids from the drilling fluid. Therefore it is necessary to optimize both filtration efficiency as well as the screen life to hinder drilled solids entering the drilling fluid. Optimum solids control can be obtained by using the understanding on how damage of the filtration cloth arises, on how to reduce it and finally on how the particles in the circulation system influence the general picture of the drilling process. When this knowledge is accepted in the industry, established and implemented in the drilling organisation; it is possible to maintain proper drilling.

This paper describes in detail the theory and field examples on how wear arise on the shaker screen cloth. As will be shown, this knowledge has been used to increase the solids control efficiency at the same time as the screen wear has been reduced by more than 90 % in field cases were 17 ½″ sections have been drilled with OBMs. The documentation is based on practical offshore result 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 drilling1. Since the early 1930s the shale shaker has been the dominating device for primary solids removal2. Additional equipment like 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, at present most shakers have a sufficient performance 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 types3. A combination of shaker and screens applicable for treating water based drilling fluids 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.

Throughout the last decades major shaker design improvements have been made. The circular motion shakers used up to 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 HES issues like hydrocarbon vapour in the shaker room, although this type of equipment has not yet reached the marked4. Sinusoidal formed screens have been implemented on some shakers to increase the flow capacity5.

Shaker operation has also been automated6. Scott6 claims that use of this automated system leads to an increase in shaker screen life. However, Scott6 do 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 120–150µm, can be achieved without problems on most shakers today by the application of the correct screen size7. There are many types of screen on the marked. The following analysis is general and do not compare any products or designs.

Screen opening and mesh sizes

Typically, a shaker screen may consist of a single metal cloth or be constructed as a series of superpositioned cloths. In some cases these cloths are tensioned in all directions while being melted onto a frame, while in other cases the cloths are melted onto frames without being tensioned. Some screens are tensioned onto the shakers directly without being attached to frames.

The screen cloths are woven with warp wires running along the cloth and weft wires running across the cloth as it is woven. The warp and weft wires can be equal or different, giving a large variation in possible screen cloth designs.

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