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.
Statfjord Field is one of the largest and oldest fields on NCS (North Sea Continental Shelf) and operates with three platforms Stafjord A, B and C. In recent years, slot recovery to drill more wells has posed big challenges to deliver wells with Gas Lift design due to extensive and cost/time consuming P&A and casing cut and pull operations. In addition to these technical challenges, improving operational excellence has driven the concept of innovative casing design with 11 ¾-in liner. This design eliminates the time spent on extensive casing retrieval operations. This reduces time and risks associated with drilling 17 ½-in section that requires changing from 13 5/8-in to 21 ¼-in BOP, higher flow rates for hole cleaning, larger volume of cutting injection, and waiting 13 3/8-in casing hangers that are crucial long lead items. Installation of 11 ¾-in liner at required depth and cementing, potential collapse of Hordaland formation due to extended time exposure, high flow rates for hole cleaning and minimizing well collision risks with producers in 8 ½-in were identified as high priority design goals in the early planning phase. To address aforementioned challenges and meet design goal in time and cost efficient way, innovative ideas were fundamental necessity. This paper discusses the integration of novel drilling approaches used in accomplishing a new gas lift well design that has opened redundant well slotson Statfjord field for drilling. Operational highlights leading to successful well delivery are: First use of dual reamer RSS BHA in 12 ¼ x 13 ½-in to minimize the rat hole and exposure time across “creeping” Hordaland formation in one run and helped 11 ¾-in liner to reach gas lift formation strength depth. Use of new generation RSS technology to drill ~930m 8 ½-in section to widen the operational flow range for hole cleaning and steering in high stick slip and collision environment. Use of modern surveying technique and magnetic ranging technology to drill 8 ½ -in section in potential collision environment. This was first ever use of dual reamer point the bit RSS BHA in North Sea and New generation RSS and special surveying technique on Statfjord.
This paper describes the successful introduction of ultraslim rotary steerable system (US-RSS) drilling in Saudi Arabia. A case study is presented where a 2167 ft power water injector redrill lateral was successfully drilled in the reservoir using an US-RSS on 2 3/8" drillpipe in conjunction with ultraslim logging-while-drilling tools, which were used for concurrent high accuracy geosteering. The existing casing design required that the sidetrack had to exit the liner in the reservoir section, since sidetracking higher up was not an option because of the risk of exposing problematic formations and pressurized zones. A number of challenges had to be overcome, including engineering design for sufficient weight transfer to be able to drill and good bit selection, since it would have been impossible to drill the planned section with a motor or conventional drilling assembly. Each stage of the job was carefully planned in detail and all stakeholders were briefed and contributed to the plan to ensure that all objectives - both drilling and well placement, could be met. The US-RSS was run in hole to drill the lateral, which was drilled with a 3 7/8" bit and concurrently opened up to 4¼". The US-RSS tool performed as planned and produced an overall rate of penetration (ROP) of 28ft per hour in a single run during the geosteering operation. All well objectives were achieved, and the system clearly demonstrated a robust technical solution to the problem. The US-RSS will enable greater reservoir access, especially in the redevelopment drilling application, and when used in conjunction with ultraslim LWD tools, can also be used to place the well in the best position for optimal additional production. Recovery rates from the field are now expected to be enhanced as a result of this technology, and without the need for drilling further new wells. Introduction Today it is well understood that further opportunities exist to enhance the production from existing fields 1 and to access as-yet untapped areas of the reservoir using a variety of redevelopment drilling techniques. Saudi Aramco faced this challenge with a re-entry program to redevelop an average of up to fifty wells annually in some of these fields, in order to recover as much remaining oil in place as possible. Due to the existing casing design and the formation pressure profiles, the only feasible size for the new drain hole is 3 7/8" diameter, if the existing well architecture is to be used for the redrilling program. However, this hole size is known to be problematic from a drilling perspective in terms of pipe buckling, achieving effective weight transfer to the bit, and the physical limitations of the mud motors that are available for this hole size. This is especially the case with regard to directional control, where the length of lateral that can practically be drilled with the motor is limited by the ability to 'slide' to control the trajectory and maximize the reservoir contact. These issues also result in roller cone bits having to be used to drill in this size, resulting in several trips per hole section, and therefore a lot of 'dead time' being required to complete drilling each well. An alternative approach is to use the recently developed US-RSS to complete these redrill laterals in a single run by rotating continuously while steering, thereby reducing the impact of the buckling forces, and by using a PDC bit. In addition, such a solution to the problem would also conceivably allow for longer laterals to be drilled while staying in the desired layer of the reservoir, thereby giving potentially greater access to the remaining oil-in-place. The US-RSS tool was developed for drilling in this range of hole sizes, specifically for this application, and can be used as part of a standard drilling system run on drillpipe. The system can also be used for coiled tubing drilling applications for 'thru-tubing' drilling 2, which has been documented elsewhere.
Statfjord field, one of the largest and oldest fields operating in the North Sea continental shelf, has been producing since early 1980s. It has three platforms, Statfjord A, B, and C, with more than 300 wellbores. Formation collapse (in the lower part of Shetland group) below casing/liner shoe in the overburden section on top of the reservoir has posed different challenges in the field. These challenges include problems in running screens and gravel packing in sand reservoirs. To respond to this challenge and focus on improving the drilling efficiency and rig cost savings, the drilling team evaluated drilling a 10 5/8 ϫ 12 ¼-in. section reaching the top of reservoir-10 m true vertical depth (TVD) above the predicted top of the Mime formation-with minimum rathole. A standard underreaming bottomhole assembly (BHA) with one ball-drop reamer leaves a 35-m to 40-m rathole below the 9 5/8-in. casing shoe, which induces different issues related to casing reaching bottom, cementing, potential packoffs due to overburden formation collapse while drilling the 8 ½-in. section in reservoir, problems in running screens, and gravel-packing operations. On two previous wells, running screens faced some challenges, and gravelpack efficiency was compromised. To cope with these technical challenges, an integrated dual-reamer rathole elimination (RHE) BHA was proposed; this would reduce the rathole to 9 m. The proposal was accepted by the operator after detailed risk assessment.This section was planned to be drilled across formations in the Hordaland group building from 16°i nclination to 30°inclination at landing on top of reservoir. To achieve the required directional control, a push-the-bit rotary steerable system (RSS) was selected. The dual-underreamer BHA with a ball-drop reamer above the surveying/logging tools and a hydraulic reamer on top of the RSS was selected to drill and underream the section in one run by minimizing rathole to 9-m. Dropping wireless communication across hydraulic underreamer made it possible to minimize the rathole to 9-m with some additional, but manageable, risks. Blind downlinks to the RSS, no real-time (RT) updates from the RSS and hydraulic underreamer, and compromising RSS steerability were the main risks identified at planning stage and agreed with the operator based on the controlling/mitigating measures in place.The Statfjord drilling team successfully addressed these challenges with an innovative solution using the dual-reamers RSS BHA to drill the 10 5/8 ϫ 12 1/4-in. section and remove the rathole in one run. Planned interval (~900 m) was drilled and underreamed to target depth (TD), with the ball-drop activated
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