The Drilling Optimization Performance in Kuwait's High Pressured Wells

Abstract

Abstract Since the spudding of the first well in the Burgan Field in 1937, continuous improvements have been made in the drilling of wells in Kuwait. This paper will address the drilling optimization performance that has occurred during the development of the deeper high pressured formations. Continued optimization performance in the deeper high pressured wells has proved to be the greatest challenge as a result of the adverse geological environment that has had to be addressed while drilling. This adverse geological environment consists of salt/anhydrite sections where formation pressure nearly equals fracture strength, pressure reversals, highly fractured thief zones and the presence of H2S. While there was some earlier deep drilling in Kuwait, development of the deeper high pressured horizons began in earnest in the early to mid 80's and is still ongoing. Four major field studies will be addressed in the paper which encompasses the majority of the deeper high pressure drilling activity. The inherent problems that had to be overcome, the solutions that were found and the problems still to be faced will be depicted in this paper. Abduliyah Field drilling has improved by a reduction of 77% in drilling days over a 12 year period. Magwa Field drilling has improved by a reduction of 58% in drilling days over a 10 year period. Minagish Field drilling has improved by a reduction of 74% in drilling days over a 14 year period. Umm Gudair Field drilling has improved drilling by a reduction of 72% in drilling days over a 13 year period. Total well depths for the above fields has ranged from 11800' to 16800'. Improvements which will be detailed in this paper will include well design changes, methods dealing with lost returns, mud cap drilling, bit optimization, and others. Introduction Oil development in Kuwait had been limited to the Cretaceous and Tertiary formations prior to the late 70's. Exploration wells drilled into the Jurassic sequence in the late 70's and early 80's discovered oil in several of the Jurassic formations. As a result of these discoveries, development drilling for the Jurassic formations began in earnest in the early to mid 80's. Within Kuwait the Jurassic sequence is the beginning of increased formation pressure. An extensive drilling program into high pressured formations proved a tremendous challenge. As a result a tremendous amount of learning took place during the initial drilling phases. The lessons learned from earlier drilling was utilized in development of improved drilling programs and job execution. This paper will address the problems encountered, lessons learned and solutions developed while developing the Jurassic productive formations. Background of Tertiary, Cretaceous, & Jurassic Sequence Before discussing the drilling of the Jurassic section some background is needed regarding the normal pressured formations uphole. The Cretaceous and Tertiary sequence which up to the late 70's was Kuwait's primary interest consists primarily of sands, shales, and limestones all normally pressured. The shale intervals are highly reactive and require inhibitive drilling fluids to prevent hydration and sloughing. The limestones for the most part vary in degrees of fracturing with the more fractured zones proving to be extremely high thief zones. The worst thief zones occur near the surface (Dammam) and in the Cretaceous sequence (Shualba). These drilling issues had to be addressed in the drilling program prior to entering the higher pressured Jurassic sequence. The Jurassic sequence is made up of formations that include fractured & oolitic limestones, salts, anhydrites, grainstones and shales. Formation pressures run from 11.0 ppg up to just below 19.0 ppg. The Jurassic section of interest ranges in thickness from 2300' to 3100'. P. 205^