Old platforms are not well known for extended-reach drilling (ERD) operations mainly due to rig and hydraulics limitations. ERD wells demand robust rig capabilities, good hydraulics systems, and equipment reliability. In addition, the well profile, rotary steerable system (RSS), measurement-while-drilling (MWD) and logging-while-drilling (LWD) tools, surveying, and new technologies are extremely important to the success in drilling an ERD well. RSS and drillpipe selection are important factors for hydraulics optimization. Surveying techniques are also important for time saving and improved efficiency. An ERD well in the North Sea Statfjord field was kicked off in the 17 ½-in. section from the openhole cement plug through a 50-m window between the 20-in. casing shoe and 13 3/8-in. casing stump, ensuring a smooth well profile and reduced doglegs compared to the whipstock window exit. The 17 ½-in. section was drilled and landed at a 79° inclination using point-the-bit RSS technology, and the 12 ¼-in. section was drilled in two runs as planned using the point-the-bit RSS withstanding more than 550 h down hole. The 9 5/8-in. liner was run and floated successfully in the ~6000-m section. Strict adherence to surveying techniques and quality control processes proved very helpful to meet Operator technical requirements. The 8 ½-in. section was drilled and landed on top of the reservoir with an inclination decrease from 88° to 35°. New MWD technology was successfully used in drilling the 6-in. section. These latest technologies as well as employing appropriate techniques help to drill ERD wells on aged platforms like those in the Statfjord field. This paper will describe the planning and execution phases of a challenging ERD well drilled in the Statfjord field.
In recent years, slot recovery to drill more wells in brownfields has posed different challenges due to extensive and time consuming Plug and abandonment (P&A) and casing cut and pull operations [SPE 173954]. In 2013, For the first time on Statfjord Field, a ruggedized point the bit rotary steerable system (RSS) and Gyro while drilling (GWD) were used to sidetrack off cement plug in 17 ½-in hole section through a narrow window (80m) between 20-in casing shoe and 13 3/8-in casing stump. This reduced risk and saved time by sidetracking and drilling the section in one run. In similar scenarios on previous wells, mud motors had been used to kickoff and sidetrack from a cement plug between the casing shoe and casing stump. Two runs were always required to complete the sections; first run with a dedicated sidetracking assembly (motor BHA) and a second run with a drilling assembly (RSS BHA). After this success another attempt was made in 2014 where 17 ½-in section was sidetracked and drilled to TD through 40m narrow window between 20-in casing shoe and 13 3/8-in casing stump in high well collision risk environment. Significant time and cost saving was achieved on this project. In 2015 a challenging well was planned where kick off had to be done through 37m window and close to six producers. Due to high risk of collision and no possible option of whipstock exit, new Point the bit RSS technology was employed to kick off in high magnetic interference environment and drill the section in one run. With the ruggedized point the bit RSS and GWD service, it was possible to constantly monitor direction and inclination in real time and thereby tracking the trajectory progress in the loose formations at shallow depth. This allowed to guard against dropping back to the mother bore and hitting the 13 3/8-in casing stump. Sidetracking in open hole from cement plug also increased formation strength at 20-in casing shoe and saved time/cost compared to whipstock exit. During execution all three wells were sidetracked successfully from motherbores in the first attempt and drilled to section TD in one run saving significant rig time and cost. This paper discusses the planning and execution phases of these three successful reentry wells drilled on Statfjord Field, one of the largest field on North Sea Continental Shelf (NCS).
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 paper aims to provide an understanding of the various measurement-while-drilling (MWD) surveying enhancement techniques applied in drilling operations at the Goliat Field located in the Barents Sea to assure accurate wellbore positioning. In high-latitude locations such as the Barents Sea, the elevated, time-dependent variations in the magnetic field create a challenge to the azimuthal measurements provided by the MWD tool. This will induce large uncertainty levels in the MWD surveys compromising the azimuthal errors established within the standard industry error models. To compensate for this effect, crustal magnetic field and time-based magnetic field disturbances were acquired to understand their impact on the MWD surveys and any associated error. This permitted drilling without compromising rig time, and the resultant reduction in lateral uncertainty was approximately 65%. With regards to true vertical depth (TVD) optimization, the nature of the reservoir targets required tight TVD tolerances. To reduce the TVD uncertainty and maximize these targets, dual inclination analysis was performed while drilling. Control checks of the continuous and static inclination data from the MWD and rotary steerable system (RSS) reduced the sensor error term of the TVD error model definition and hence produced an improvement of up to 67%. Seven wells have been drilled in the Goliat Field based on the methodology described in this article. In the planning phase, it was noticed that extra surveying techniques would be required to achieve the objectives for lateral and TVD placement. Survey management workflows were implemented to ensure consistency with regards to surveying accuracy. Drilling and environmental challenges encountered in the Barents Sea push the boundaries of every aspect of current surveying techniques. Adherence to survey management procedures and understanding of the impact in the measurements generated by the disturbance in the magnetic field improved efficiency in the drilling operation and helped to achieve the critical well positioning objectives for this field.
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