Operational Aspects of Drilling and Completing Horizontal Wells Offshore Abu Dhabi

Abstract

Abstract Since June 1989, Zakum Development Company (ZADCO) has drilled and completed eight horizontal producing wells in Upper Zakum Field and one well in Umm Al Dalkh Field. With numerous development drilling locations remaining in Upper Zakum Field, the potential for increased usage of horizontal techniques is significant. Most of the required production platforms are in place and most of the remaining slots are dedicated for medium and high departure wells. One high departure horizontal well with a horizontal section extending more than 9000 lateral feet from the platform has been successfully drilled and completed. In addition, the potential to sidetrack numerous existing low/medium/high departure wells for horizontal drilling is significant. In fact, five of the nine horizontal wells drilled to date were reentry sidetracks and four were drilled from the surface. The purpose of this paper is to present an operational overview of ZADCO's experience with horizontal wells. Topics of special interest include:the unusual horizontal well trajectories required offshore (i.e. high-departure wells),efforts to minimize top-hole doglegs to minimize torque and drag and reduce casing wear,a technical and economic comparison between sidetracking and drilling new wells,a discussion of current and future completion techniques, andstimulation techniques. Introduction Discovered in 1963, Zakum Field is the fourth largest field, and the largest offshore field, in the Middle East. Early development efforts focused on Lower Zakum Field. Development of Upper Zakum Field began in 1977. Thus far, a total of 310 wells have been drilled and completed in the 465 square mile Upper Zakum Field, most of which are deviated wells with dual completions. More than one hundred infill wells remain to be drilled. There are three distinct groups of limestone reservoirs in Upper Zakum Field, the Thamama I, II, and III. Well spacing ranges from 2500 to 5000 feet. Water injection was initiated in 1984 to maintain reservoir pressure and maximize profitability. ZADCO first studied horizontal drilling in 1988 as a potential means to optimize the development of Upper Zakum Field. Operating on behalf of Abu Dhabi National Oil Company and in conjunction with Abu Dhabi Marine Operating Company, ZADCO drilled the first horizontal well in the Arabian Gulf in 1989, in Upper Zakum Field.1 The advent of horizontal drilling technology has provided ZADCO with a unique opportunity to develop Upper Zakum Field using state-of-the-art technology. Initial results of the horizontal trial program have been excellent from both operational and reservoir management viewpoints. Present plans include increased usage of horizontal techniques, including dual horizontal producing wells and horizontal injection wells.