Design of Water Based Drilling Fluid Systems for Deepwater Norway

Abstract

The technical demands placed on drilling fluids used in the deep waters of Norway differ dramatically from those encountered in any other deepwater basin. Unlike the deepwater of the Gulf of Mexico, West Africa or Brazil, seafloor temperatures here can dip as low as -2.5° C (27.5°F), with low ambient surface temperatures the year round. These characteristics combined with constantly changing sea conditions and some of the world's most stringent environmental restrictions, makes the engineering of drilling fluid systems for Norwegian North Sea wells an arduous effort. This paper describes the innovative development and qualification of a water-base drilling fluid system engineered for a well to be drilled in 837 meters (2745 ft) of water off Norway. The pre-qualified fluid was required to inhibit hydrates under normal drilling conditions and possess excellent shale inhibition characteristics to support hole stability and avoid bit balling. Since the primary objective was to obtain a non-contaminated formation water sample, the system must possess superb fluid loss control so the operator could avoid a full drill stem test, thereby saving some US$8 million. Furthermore, the qualified system would have to meet local environmental regulations for offshore discharge of cuttings and excess fluids. The authors will discuss the development protocol, the qualification of the novel fluid system and its application in the technically demanding Norwegian well. During the development phases, two hydrate testers were qualified and employed in both designing the fluid and to monitor its hydrate inhibitive tendencies during drilling. In addition, the particle size distribution and polymer concentration were engineered to reduce the filtrate invasion, while polymers were specially selected for improved rheological parameters to cope with the cold temperatures. The behavior of a number of glycols and salts were characterized prior to the start of drilling. The practical approach to qualify the novel fluid system will be explained in detail, emphasizing its use as a guideline to help non-fluid specialists design drilling fluids for this unique deepwater environment. Introduction The exceptional technical requirements associated with engineering drilling fluid systems for the deepwater environment have been well documented in the literature1,2,3,4. Regardless of the location, wells constructed in water depths exceeding 458 meters (1,500 ft) present a host of distinctive concerns that must be addressed early in the planning stages and monitored constantly during the drilling operation. If left unchecked, these troublesome phenomenon pose serious safety, environmental and economic risks and in some cases can even jeopardize the project itself. Among the most threatening of the fluid-related concerns in the deepwater environment are the constant risk of lost circulation, intrinsically low pore pressure to fracture gradient differentials, ineffective hole cleaning in young gumbo shales, unique environmental and logistics considerations, wellbore stability, mud density and the potentially disastrous formation of gas hydrates in the cold water atmosphere, among others.

Estudo das modificações das propriedades físico-químicas de fluidos de perfuração aquosos

“…A formulação ideal permite que um fluido de perfuração apresente um comportamento quimicamente estável, seja inerte as rochas a serem perfuradas, seja capaz de aceitar tratamentos químicos e físicos, apresente baixos potenciais de corrosão, abrasão e agressão ao meio ambiente e, além disso, permita o seu bombeamento por todo sistema de circulação (THOMAS, 2001;KEMBAIYAN e KESHAVAN, 1995;NASIRI et al, 2009). Essas características também podem ser controladas pelas alterações nas composições químicas desses fluidos, o que pode minimizar ou, até mesmo, eliminar diversos problemas presentes na indústria petrolífera, tais como: a perda da circulação do fluido, a ineficiência na limpeza do poço e a possibilidade de danificar o meio ambiente (SORGARD et al,2001).…”