TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDrilling on the Troll Oil field has been challenged by the need for long and extensive horizontal hole sections while strictly controlling true vertical depth.The horizontal reach has been extended from initially about 800 meters to more than 4,400 m in a single well bore using the latest generation of Rotary Steerable Systems. At the same time, multilateral drilling technology has become a standardized application on Troll with up to four reservoir sections completed per well.

Exploiting the Troll reservoir in the Norwegian North Sea requires horizontal drilling through relatively loose sandstone and local hard calcite-cemented zones. Depending on the orientation of the calcite interval, and the drilling parameters when entering or exiting the calcite interval, the bit can be forced aside to create a potentially severe local dogleg. High local doglegs introduce significant stresses into the drilling system that can rapidly accelerate fatigue of the BHA components and connections. Until recently, the driller could only identify local doglegs in the vertical plane when a rapid change of a near-bit inclination measurement was reported to the surface. No means were available for detecting azimuthal doglegs in the horizontal plane. A new downhole dynamics tool, positioned above the rotary steerable system, is capable of measuring the bending moments in the BHA generated by side forces at the bit. If transmitted to the surface while drilling, the BHA bending information allows early detection and quantification of local doglegs independent of their orientation. The paper explains the details of the bending moment measurement and the bending response of the BHA to local doglegs. Several field examples demonstrate the sensitivity of the measurement and the remedial actions initiated in response to the downhole BHA bending information. In one case drilling was stopped earlier than planned due to the detection of an extremely severe local dogleg, and a potentially catastrophic failure close to TD was avoided. Introduction The Troll field is one of the largest offshore gas fields in the world, extending into four blocks in the Norwegian North Sea over an area of about 770 square kilometers. It consists of two main structures, Troll East which is essentially a dry gas structure, and Troll West which contains a thin but exploitable oil column (12–26m) below a thick gas column. The Troll West reservoir consists of the Upper Jurassic Sognefjord formation, a stacked series of sandstone units lying at a depth of approximately 1500 m below sea level. These sandstone units were formed by shoreline development on the northwestern edge of the Horda Platform during the Upper Jurassic. Clean medium to coarse-grained target sandstones alternate with finer, poorer quality non-target intervals. The shallow depth of burial has preserved good to excellent reservoir properties that are only locally reduced by calcite cementation. Calcite nodules and stringers up to several meters thick, derived from shell material within the sands, occur throughout the reservoir and can create difficulties for drilling. Many of the stringers have stratigraphic significance, but predicting their distribution is difficult as they are only locally developed. Other calcites are randomly scattered throughout the reservoir. The photograph of the Bridport Sands on the Dorset Coast of the UK shown in Figure 1 provides a good impression of the structure of the calcites in the Troll reservoir. The oil reservoir is exploited through long horizontal sections of up to 3,200 m in length. Within the limitations posed by the thin nature of the oil column, these wells are geosteered through the reservoir to avoid non-productive zones and to keep the well path closely (+/− 0.5 m TVD) above the oil water contact. Fiksdal et al.1 have described in an earlier paper the work that has led to a better understanding of the drilling challenges posed by the calcite cemented intervals. The paper also describes the step change in drilling performance realized by introducing rotary steerable systems2 (RSS) with PDC bits.

The North Sea has always been a pioneer for the adoption of remote operations services (ROS) in offshore drilling applications. Drilling services such as Measurement While Drilling (MWD), Logging While Drilling (LWD) and/or mud logging (ML) have been performed with an element of ROS for over the last two decades. Early adoption of these remote services delivered initial benefits to operators such as reducing HSE risks related to the travel and accommodation of field service employees at offshore rig sites. Meanwhile service companies were able to explore the added efficiencies gained by having multi-skilled employees providing a higher level of support to customers while also gaining additional agility to manage their personnel through tighter market cycles. The mutual benefit of this early adoption created a solid foundation for ROS to expand the scope of influence in drilling operations to include Directional Drilling (DD). Despite the maturity of ROS within a select community of operators in the North Sea, the industry standard for service delivery in offshore operations has continued to require field service employees to perform DD, MWD, and LWD services at rig sites until this past year. With the COVID-19 pandemic in 2020, operators and service companies were quickly and abruptly confronted with the challenges of new HSE regulations, travel restrictions, and increased financial scrutiny. ROS presented a tailored solution to not only sustain business continuity but also create added efficiency, consistency, and risk management. Over the course of 2020, adoption of ROS rapidly accelerated across offshore operations in the North Sea and reached up to 100% penetration in key sectors. This tremendous achievement has made a significant impact on project performance and HSE efficiencies by ensuring on time service delivery while reducing personnel on board (POB). In addition, as more operators and services companies explore ways of reducing their carbon footprints and achieving a net zero future, ROS has proven to be a way to significantly reduce carbon emissions associated with transportation and utilities of offshore personnel. This paper discusses the methods that enabled a record high adoption rate for ROS and explores the critical components of its success. It illustrates the management of change in service delivery processes, the introduction of new technology to unlock greater productivity and synergies, and the new approach to design the core competencies needed to support ROS. It also describes the need for flexible ROS service models to meet the specific project needs of various operators. The paper concludes with the numerous benefits realized through ROS such as improved performance and consistently reliable service delivery. The paper also examines the resulting carbon emission reduction, how to quantify it, and the role ROS plays in achieving a net zero emissions future.