Application of Water Based Drilling Fluid - Total Fluid Management

Abstract

Abstract North Sea area environmental practice and focus on reduction of drilling costs have limited the discharges of drilling fluid and drilling fluid chemicals to the sea the last years. A method for efficiently recycling water based drilling fluids has been developed. This recycling is conducted in a way beneficial both for the drilling fluid supplier and the operator. Contaminated fluid (slop) is brought back onshore for treatment and reusable fluids from the slop treatment are brought back into the drilling fluids. The current paper show the total fluid management system operates for offshore drilling. This includes the compensation format being beneficial both for the drilling fluid supplier and for the operator. Furthermore, the paper describes the different actions taken to reuse water based drilling fluids, and how these actions generally reduce total drilling costs. The paper also describes the different systems implemented to minimize loss of drilling fluids and recycling of drilling waste streams. Also addressed are the challenges in establishing sound targets for optimum reuse depending on fluid systems, balancing economy and environment. Introduction Offshore drilling operations involve drilling fluids to maintain well control and to transport cuttings out from the well. Traditionally, drilling fluid remnants and drill cuttings from these operations has been regarded as drilling wastes and treated accordingly (1). Historically, effort has been invested in exploring waste minimization opportunities (2,3,4). Fairly recently a new trend has appeared. This trend is the holistic approach to solving both the drilling and drilling waste problems(5,6). The essence of this philosophy is that one has to design input chemicals that are used for drilling purposes, bearing in mind that none of the chemicals should compromise a recycling solution. Prioritized waste minimization efforts are described by the famous 5R waste minimization hierarchy, where the top R's; reduction at source, reuse and recycling of material are believed to produce rewarding returns. Some will argue that this is resource management as opposed to a risk based waste disposal decision strategy, as the ultimate goal of waste minimization is to avoid deposition of waste. Re-use of oil based drilling fluids has been common for years (5). This re-use has been driven by the need to minimize the consumption of relatively costly fluids. Water based drilling fluids are less expensive and were therefore discharged to sea after finishing the drilling operation prior to the middle 1990s. In a field trial Statoil (8) demonstrated the viable economical benefit, along with reduced discharges to the environment when water based drilling fluid was re-used as suggested bye S rbye (7), and has later been practice for a lot of Norwegian North Sea operations (5). Re-use of drilling fluids has been common for both water based and oil based drilling fluids during the last years. The challenge still to be solved is the handling of the drilling waste residues. Currently, it is not permitted to discharge oil wet cuttings on the seabed. This includes the discharge of cuttings from drilling operations with synthetic drilling fluids for most Norwegian operations. The primary focus of this article is therefore to outline methods for re-using drilling fluid and handling of offshore oil containing drilling waste on and offshore.