Drilling a re-entry well is a routine operation on mature fields. Several techniques are generally used for re-entry operations including cement plug sidetrack and whipstock sidetrack (Hussain et al. 2016). Often the completion string is pulled prior to performing the sidetrack operation but when it is not, one calls this operation a Through Tubing Rotary Drilling (TTRD). Benefits of TTRD wells include lower cost to access small hydrocarbon reserves. Through-tubing wells are usually drilled with small hole sizes and in Norway such wells are generally drilled with 5 7/8-in. or 5 ¾-in. hole sizes. In this paper we present the case of a through-tubing well drilled with an uncommon 3 ¾-in. hole size. This paper will: Present the reason for planning such a sidetrack: drilling 3 ¾-in. hole is a rare operation on the Norwegian Continental Shelf (NCS)Describe the solution selected for the operation, including the directional plan, the whipstock setting operation and the 3 ¾-in. bottom hole assemblySummarize the risks and compensating measures associated with this solution, including the low buckling margins in this well planned at inclinations higher than 90°, the low tolerances on the downhole connections that could lead to a twist-off, the limited experience with the directional behaviour of such a slim bottom hole assembly, the bit design.Present the results of the successful operation: this rare 3 ¾-in. hole drilled on the Norwegian Continental Shelf was drilled successfully and below budget.Find the main drivers that will make this solution portable to other situations This case study demonstrates how detailed and thorough planning based on modelling led to the successful delivery of a rare well design at first attempt. It is an objective of this paper to share some key elements that will be useful for the planning of similar operations in other wells in the future.

The main objective of this paper is to share the experience of the first Dual reamer bottom hole assembly (BHA) design implemented off-shore Norway, Gullfaks field, 17 ½ × 20-inch section. It presents the drilling challenges, innovative bottom hole assembly and the first world wide application for the Electro-magnetic receiver sub fully integrated with rotary steerable system (RSS) Hole enlargement while drilling (HEWD) became a well-known application, and they are widely used to support several well intervention objectives like; i) Accommodating un-common casing design. ii) Reduce operational risk such as high equivalent circulating density (ECD). iii) Optimized casing and completion programs. There are two main types on hole enlargement tools, based on activation mechanism: ball-drop using a ball to Activate/De-activate the reamer, and hydraulic on demand triggered by changing flow rate on a predefined specific range, so called ‘Indexing’ for Activation/De-activation of the reamer. Both carrying a common implicit risks and limitations, where reamers have to be positioned above logging while drilling tools (LWD) so that the enlarged hole does not impair the quality of the formation evaluation measurements, or compromise the bottom hole assembly stabilization. This results in a rat-hole of 40-50 meters at the section target depth (TD), consequently challenges the casing running, casing cementing job, and drilling next sections with potential risk of cement pack-off around bottom hole assembly. Today in the industry, these challenges are usually addressed by an extra dedicated run for opening the rat-hole. Collaborative efforts between operator in the North-sea and a Service Company to address the risk and limitations associated to the hole enlargement while drilling design. Dual Reamer System developed to reduce the rat-hole length to minimum instead of 40-50 meters, and to eliminate the extra dedicated run for opeing the rat-hole. The innovative approach planned to drill to section target depth (TD) using upper ball drop reamer, tool positioned 45 meters behind the bit for Hole Enlargement While Drilling, then pull back to position the bit at rat hole shoulder, de-activate upper reamer (ball drop system), and activate the lower hydraulic on demand reamer to eliminate the rat-hole. A Gyro while drilling integrated into the BHA along with 9-in world first electro-magnetic receiver sub mounted on the top of the hydraulic on demand reamer. Providing a full integration, and securing a real time communication with the RSS in a critical and challenging Anti-collision situation. The unprecedented approach successfully implemented on Gullfaks field, 17 ½ × 20-inch section drilled to target depth (TD) in one run, with all objectives met on directional control in tight Anti-collision scenario, and measurements and logging while drilling. The Dual reamer BHA along with the Electro-magnetic receiver sub proven efficient steering capability and reliability, which led to significant improvement in the drilling, casing running and cementing operations

This case study aims to share the experience and improve the understanding of downhole shock and vibration and demonstrate how it can be prevented using thorough offset analysis, an advanced bit design, downhole mechanics module, and detailed drilling roadmap. The new approach delivered a step change in the performance of the 17 ½-in. section in Valemon field, in the Norwegian sector of the North Sea. Employing a one-run strategy through this extremely demanding section could eliminate the need for a dedicated motor run to withstand high shocks through the sandy interval with interbedded limestone and cemented sand layers. Using a point-the-bit bottomhole assembly (BHA) with a detailed drilling roadmap for every group of formations secured smooth drilling, pull out, and running of the intermediate 14-in. × 13 3/8 in. casing to provide integrity to drill 12 1/4-in. section. An advanced bit design balanced drilling with low aggressiveness through sand without compromising the performance through the interbedded limestone stringers and claystone. The conical-shaped cutter placed behind the main PDC conventional cutters successfully controlled the depth of cut through the sandy intervals and mitigated the downhole shocks. A detailed drilling roadmap was developed to define formation-specific drilling parameters to mitigate the shock-related failures on similar lithology. A downhole drilling mechanics module was used to provide real-time axial, lateral, and torsional shock and vibration data, which enabled adjustment of surface drilling parameters accordingly.

In this case study, we present the use of a new look-ahead resistivity technology to solve a challenge on the Valemon field where the top of the reservoir could not be mapped from surface seismic. The objective was to extend the overburden section deep enough to secure sufficient formation strength at the casing shoe while eliminating the risk of accidental drilling into the reservoir below. The application of the new technology secured standard casing design, and eliminated the extra time and costs associated with implementation of the managed pressure drilling technique. The target was to extend the 12 ¼-in overburden section 10-15m TVD into the Viking Group, as this formation generally provides sufficient formation strength for the 9 7/8-in casing shoe to enable conventional drilling of the following reservoir section. As there was a risk that the Viking Group could be absent or very thin in this area of the Valemon field, the look ahead measurement was used to monitor the formations ahead of the bit while drilling. Detection of higher resistivity ahead of the bit indicating an approaching reservoir would enable stopping prior to drilling into it. No reservoir response was detected ahead of the bit, and this enabled a safe extension of the 12 ¼-in section into the Viking Group as per the objective.

The objective of this paper is to share the results obtained from in-depth analysis using a down hole mechanics and dynamics monitoring sub, which lead to the first successful Gullfaks Satellite 14 ¾ x 17 ½ -in Rathole elimination operation through challenging lithology. Shallow gas is encountered in the Gullfaks South area at a true vertical depth of between 335-339m (from MSL), and a casing design incorporating a 16-in liner is utilized to isolate this interval. A 14 ¾ x 17 ½ -in section is then drilled to isolate weak and unstable formations, and in all previous wells this section was drilled with a two run strategy. The first run to drill to section target depth (TD) while hole opening, followed by a dedicated second run to open the rathole. An opportunity was identified to improve well construction performance by eliminating the dedicated run to open the rat-hole, and tailoring the bit design to overcome the challenging lithology and high levels of shock and vibration seen on offset wells. Detailed pre-job planning and BHA design analysis was combined with new downhole technologies to overcome these challenges. Dual reamers were used within a Rotary Steerable System (RSS) BHA to drill the 14 ¾ x 17 ½ -in section and eliminate the rat-hole in one run. This innovative approach involved drilling to section target depth (TD) using an upper ball drop reamer, tool positioned 45 meters behind the bit for hole enlargement while drilling, and then pulling back to position the bit at rat-hole shoulder. At this point the upper reamer was de-activated and a lower on demand hydraulically activated reamer, mounted directly above the RSS was opened to eliminate the rat-hole. Due to excessive shocks & vibrations experienced on offset wells, a down hole drilling mechanics & dynamics sub was utilized to provide real-time information about downhole forces and BHA motions, combined with a tailored bit design to control depth of cut in sandy intervals. This unprecedented approach resulted in 2.5 days saving.