Abstract

Effective removal of contaminants from drilling fluids is widely accepted as a key factor in achieving optimum drilling performance and reducing fluid cost. Current shaker technology reflects incremental advances in functionality related to size, vibration and screen technologies. This paper describes the evaluation process of an alternate device, Cubility's MudCube, by Petrobras. The MudCube evaluation took place on a test site in Stavanger, Norway, with the goal of reproducing operational conditions similar to those in deepwater wells on the Brazilian coast. As drilling environments become increasingly complex and the industry increases its reliance on unconventional resources to reduce costs and control risks, the lightweight vacuum conveyer system (VCS) seems to be an attractive way to handle drilling fluids and solids. Studies show a potential improvement in drying capacity, safety and environmental risks during drilling operations. The equipment presented low noise level and no vapor emission, easy operation and avoids direct contact with the fluid. The elevated processing flow rate makes the system attractive for offshore use, where space is a major limitation. The water content in the processed fluids was reduced, which led to the possible reduction of low gravity solids content. Test results indicate a good potential to separate cuttings with organic phase content lower than 6.9%, the present environmental limitation for discharge in Brazil. In a conservative scenario, this fact would allow the drilling of a 17 ½ in phase without ROP constraints (often limited by the conveying and drying systems). Reducing waste, costs, and health, safety and environmental impacts are always top of mind within the petroleum industry. For decades, the same shaker technology was used with no viable alternative. If used in Brazilian offshore drilling, this alternate technology may result in significant gains in performance, coupled with notable cost reduction.

1 - Introduction

It is known that drilling fluid quality is a key element to efficient drilling. The best and cheapest way to keep the fluid quality while drilling, besides minimizing waste generation, is through the use of an efficient solids control system. Its main function is to remove drilled cuttings and fine particles, helping to maintain fluid properties inside design requirements. Common drilling problems are related to the presence of drilled solids in the fluid. The higher the solids contents in the mud the smaller the rate of penetration, which increases the drilling cost and may affect wellbore stability problems due prolonged exposure of certain rock formations [1].

Traditionally, the primary solids separation has been performed by shale shakers. Besides cuttings separation, shale shakers also affect the performance of secondary solids removal equipment, such as desilters, desanders and centrifuges. Shale shakers have been used since the decade of 1930 [2]. The drive force for separation comes from screen vibration. The vertical component generates acceleration which enables fluid flow through the screens and the horizontal component transport the cuttings along the screen. Although several improvements have been added to the equipment the main separation concepts remain from the original devices.

Searching for new concepts in solids separation, aiming efficiency and HSE improvement, PETROBRAS decided to test a solids separation system named MUDCUBE, a Vacuum Conveyer System (VCS), which already showed good performance in some onshore and North Sea offshore operations. The VCS is shown in Figure 1.

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