Abstract

Drilled cuttings contaminated by non-aqueous fluids (NAFs) are the waste generated by oil well drilling activities. Over the last twenty years, studies have been conducted to assess the effects that these residues have on the environment in both offshore and onshore scenarios. More restrictive environmental legislation and the need to reduce drilling costs (exploration and production) have led to the optimization of solid-liquid separation. Currently, in Brazil, the environmental offshore discharge threshold for synthetic materials is 6.9 % by mass. Microwave radiation is a promising technology to remove the organic phase of these drilled cuttings. This paper presents microwave heating technique as a method for the treatment of contaminated drilled cuttings. This drying methodology was applied to contaminated cuttings and studied through a Design of Experiments (DOE), where the manipulated variables were NAF concentration, specific energy and mass. The responding variables were residual n-paraffin content, percentage of n-paraffin removed, mass flow and mass of n-paraffin removed per energy unit.

Introduction

The world's dependence on oil is an incontestable issue. This necessity creates a continuous search for this energy source, which is found in increasingly critical conditions. In addition to this difficulty, there are growing demands for sustainable oil exploration and production, including more stringent environmental laws. Thus, companies not only aim for profitability but also sustainability. Oil drilling has encountered increasingly challenging scenarios due to the difficulty of finding large oil reserves; moreover, the operational window associated with these scenarios has become increasingly narrow. Thus, to provide continuity of oil exploration in Brazil, it is necessary to critically analyze the processes involved and search for ways to optimize them [1].

During the drilling process, a fluid is used to remove the cuttings generated by the bit from the well. With the evolution of the drilling process, several types of drilling fluids emerged. The classification of a drilling fluid is most commonly made on the basis of its composition [2]. These fluids are classified into water-based fluids (WBFs) and non-aqueous fluids (NAFs).

Cuttings contaminated with NAFs are the major waste from drilling activities. In offshore scenarios, these cuttings must be decontaminated of the organic phase before they can be discharged into the sea. The treatment of this material is possible onshore, but it is very expensive and the treated cuttings are still a residue, which disposal must follow specific regulations. Therefore, when economically and technically feasible, offshore decontamination followed by discharge at the location is the most attractive option. In Brazil, to discharge overboard, the limit on residual n-paraffin content is 6.9 % by mass. This is the same standard used by the US EPA [3].

There is a solids control system associated with the drilling process, which involves several pieces of equipment and promotes the solid-liquid separation described above [4]. The goal of modern solids control systems is to reduce the overall cost of drilling operations by removing solids and minimizing the fluid loss associated with these solids.

The equipment currently used for drilled cuttings treatment is the cuttings dryer. This apparatus, which is actually a vertical centrifugal filter, is used to fit the solids from the solids control system to environmental laws, thereby recovering a larger amount of the drilling fluid. However, the recovered fluid has a high solids content, which undermines the fluid quality [4]. Even with the use of decanter centrifuges, the recovered fluid does not satisfy established quality standards.

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