Successful Drilling of Oil and Gas Wells by Optimal Drilling-Fluid Solids Control – A Practical and Theoretical Evaluation

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.

Towards Closing the Loop on Drilling Fluid Management Control

“…20 to 30 % of this NPT can be attributed to poor drilling fluid quality. Relatively simple optimisation studies have clearly showed the potential for reducing NPT by 10-20 % through proper control of the drilling fluid properties (Dahl et al, 2006). To exploit its full potential, the studies also demonstrated the criticality of automation of the drilling fluid processing.…”

Criticality Testing of Drilling-Fluid Solids-Control Equipment

“…Significant savings may be gained by running the equipment efficiently, and it is therefore crucial to continuously monitor and optimize the solids-controlequipment operations with respect to such details as screen wear, screen selection, and flow distribution. Optimization studies (Dahl et al 2006) have demonstrated the importance of the operator's skills and routines for the inspection, changing, patching, and washing of screens and the appropriate use of the regulation possibilities of the equipment. When the efficiency of the shaker is considered as part of the procurement and good operational routines are implemented and maintained, the drilling cost for the well will be lower.…”

“…The shaker-screen configuration also has a significant impact on capacity (Dahl et al 2006). To obtain equal test conditions for all the shakers, the filtration screens were set to have a cutpoint equal to API 170 (API 2010).…”

“…Additional equipment (e.g., desilters, desanders, and centrifuges) was often used in the past to maintain proper solids control, but experience in recent years has demonstrated that, although dependent on correct operational procedures, several types of shale shakers have sufficient performance to act as the sole solids-control devices without the use of desanders and desilters.Despite often being the only measure for solids removal, the selection of shale shakers, the screening, and the establishment of operational procedures are often based on biased information (Dahl et al 2006). In addition, it has been recognized that methods and criteria for the verification of shale shakers have not been sufficiently qualified and standardized.…”

“…Despite often being the only measure for solids removal, the selection of shale shakers, the screening, and the establishment of operational procedures are often based on biased information (Dahl et al 2006). In addition, it has been recognized that methods and criteria for the verification of shale shakers have not been sufficiently qualified and standardized.…”