This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 119506, "How Continuous Improvement Led to the Longest Horizontal Well in the World," by Kumud Sonowal and Bjarne Bennetzen, Mærsk Oil Qatar A/S; Patrick Wong, K&M Technology Group; and Erhan Isevcan, Schlumberger, prepared for the 2009 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 17–19 March. The paper has not been peer reviewed.

In May 2008, Mærsk Oil Qatar completed drilling its Well BD-04A with a horizontal length of 35,770 ft. It was reported that this well set records for both the longest well, at 40,320 ft measured depth from the rotary table (MDRT), and the longest along-hole departure of 37,956 ft. The use of new techniques allowed existing constraints to be challenged and overcome successfully. These achievements were possible by applying sound engineering principles and continuous optimization during the field-development phases. Even when constrained by limitations, such as rig capacity, major step changes were achieved by optimizing basic operating parameters.

Introduction

The Al-Shaheen field is approximately 80 km northeast of the Qatar peninsula, Block 5 in Fig. 1. The Kharaib formation is a laterally uniform carbonate deposition generally 80 ft thick and has a reservoir target of approximately 25 ft. The Shuaiba formation exhibits lateral facies changes and permeability contrasts. Its thickness generally is 200 ft, with a reservoir target of approximately 20 ft. The Nahr Umr formation is a 20-ft sand sequence with reservoir targets of 5 ft of permeable sand or less.

The decision to develop this field by use of long-reach horizontal wells was driven primarily by the large aerial extent of the accumulation, poor productivity of vertical wells, and the number of platform locations required if a conventional approach with vertical or slant wells was pursued. The length of these horizontal wells has been extended during the course of the development, and some of these wells are pushing the limit that can be achieved with today's technology. To further enhance oil recovery from the Al-Shaheen field, it was decided, in 2007, to drill even longer wells and initiate measures with detailed engineering analysis to expand the horizontal extended-reach-drilling (ERD) envelope beyond industry experience.

Well BD-04A

At 40,320 ft MDRT, Well BD-04A was the longest well drilled, achieving the longest reach of 36,238 ft. The horizontal section was 35,770 ft [i.e., from the first survey with inclination above 86.0° at 4,550 ft MDRT to total depth (TD) at 40,320 ft], with 35,449 ft of continuous reservoir exposure.

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