A Case History of Casing Directional Drilling in the Norwegian Sector of the North Sea

Abstract

Abstract In January 2007, ConocoPhillips completed what is believed to be the first well directionally drilled with casing using wireline retrievable bottom hole assemblies from an offshore installation. ConocoPhillips has considerable experience with this technology in reducing drilling days on predominately vertical land wells in South Texas. It was desired to determine if the same benefit could be realized in the offshore environment; where directional drilling is required. A candidate development well was identified in Norway on the ConocoPhillips operated Eldfisk Bravo platform that could benefit from advantages seen with Casing while Drilling. Two land based tests were conducted to confirm the ability to conduct casing directional drilling in wells similar to those expected in Norway. Simultaneously, a detailed plan for drilling the well in Norway was developed. Two production casing strings (10 ¾-in. and 7 ¾-in.) were successfully drilled directionally through the overburden section on the Eldfisk well. The well had a complex 3-dimensional well path with inclination up to 60°. All running and retrievals of the BHAs was planned to be done with wireline and a purpose-built traction winch system rated to a working load of 40,000 lbs. Once the 7 ¾-in. production casing was cemented, the casing string was converted to a production liner with an expandable liner hanger and the upper section of 7 ¾-in. was retrieved. In all, 10,968 ft of the 13,600 ft well was directionally drilled with casing. Introduction ConocoPhillips has actively used Casing while Drilling (CwD) technology in more than 150 wells in South Texas since 2001. This technology has contributed to solving downhole problems associated with lost circulation and sloughing shales. 1,2 It has been a factor in providing excellent hole conditions. From a well control standpoint, CwD technology is advantageous in that it provides the ability to circulate the entire time that the BHA is being pulled or run into the well with wireline. This leaves the pipe at or very near to bottom during the drilling process; even with the BHA out of the well. All of these factors have allowed COP to significantly reduce trouble time and overall days required to drill wells in areas of South Texas. While there have been some directional CwD applications on land, the technology was not proven in the offshore environment. An obvious question for COP was "Can the benefits seen using CwD technology on onshore vertical wells be realized in the offshore environment where directional drilling is required?" In reviewing the global portfolio of drilling operations, a candidate well, the 2/7B-16A well was identified in the Eldfisk Field on the Eldfisk Bravo platform (Figure 1) located in the Norwegian Sector of the North Sea. The Eldfisk Field produces from the Cretaceous Chalk and has been in production since 1979. Eldfisk Bravo is a relatively small, 20 slot production platform set in 1978 with an integral platform drilling rig. An almost constant re-development program is required to maintain the field production rate. Drilling issues related to this work include complicated slot recovery work, drilling problems such as lost returns near the top of the reservoir, high levels of drill gas while drilling the Miocene and Eocene intervals in the overburden and difficult hole conditions commonly experienced during tripping operations while drilling production wells.