Microwave paddle dryer como alternativa para a secagem de cascalhos da perfuração em ambientes offshore

Abstract

In the process of drilling oil wells, the rock fragments generated by the drill are called "drill cuttings" and are transported to the surface by the action of drilling fluid. This drilling fluid has various functions to perform the drilling operation safely and stably. It has specific characteristics that are needed for the process, which result from various additives included in its composition. However, organic-based fluids contain olefins in their formulation, which are toxic to the environment. For this reason, the current limit in Brazil for the content of organics from drilling fluid in the drill cuttings is 5.9% by weight for offshore disposal. Due to increasing environmental restrictions, this value is expected to be significantly lower in the near future. The mixture of drill cuttings and drilling fluid is separated by a series of equipment in sequence, forming the solid control unit. However, the efficiency of these separating machines is already close to the maximum allowed by law. This demands the conception of a new machine to ensure environmental adequacy for the disposal of contaminated drill cuttings. The equipment proposed in this work is the Microwave Paddle Dryer, which uses microwaves for drying contaminated drill cuttings combined with bed agitation. The potential of the equipment was evaluated for the decontamination of drill cuttings with organic components in batch mode at three rotation speeds of the agitation axis at values of 5, 20, and 35 rpm. Operational control and safety aspects were also studied. For the intermediate speed of 20 rpm of the agitation axis, the equipment was able to decontaminate carbonate rock drill cuttings contaminated with organic-based drilling fluid from an initial content of 8.4% organics and 11% water to a residual average organic content in the bed of 4.16%. It consumed 0.35 kWh of electric energy per kg of contaminated drill cuttings in a batch of 71 kg. The central regions of the bed reached residual organic contents below 2%, and other regions showed residual contents above 10.7%. This inequality in separation comes from phenomena like vapor condensation on the internal hull and the non-uniform distribution of the electromagnetic field generated by the microwaves. Tests were also conducted for particle dynamics in the bed in continuous mode using dry sand and without the application of microwaves. The goal was to study operational parameters related to material flow in the bed for future adaptation for continuous drying. In the bed dynamics tests with sand, the influence of variables such as rotation speed of the agitation axis, overflow height, and inclination were evaluated. The responses analyzed were the bed holdup and the speed of the sand particles. All three independent variables were significant for material retention in the bed. Increasing the overflow height contributed to an increase in bed holup, while increasing the rotation speed of the agitation axis and inclination contributed to a reduction in the bed holdup. The sand bed dynamics tests also showed phenomena like the formation of a region above the agitation blades that affected the superficial displacement of particles in the bed and was related to critical values of the agitation axis rotation speed and bed inclination.