Ultraslim Rotary-Steerable System Gives Greater Reservoir Access in Saudi Arabia

Abstract

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.