Norsk Hydro's Troll Olje field will require about 25 multilateral wells in order to drain the field using the existing sub-sea template structure. Prior to the development of the Isolated Tie-Back System (ITBS™) described in this paper, three multilateral wells had been installed on the Troll Olje field using System 4503. On these TAML Level 4 wells, junction isolation was achieved with special cement and a resin squeeze. Junction related production problems were experienced on two of the wells with lumps of resin flowing back and plugging surface equipment. One well cleaned up rapidly, whereas the other is currently shut down. The MLT operations on these wells had been completed in 22 days, 17.9 days and 14.6 days, respectively. Although all wells were technically successful and the trend was good there would be a lower limit around 12 days due to all the milling operations required establishing the initial exit and the re-entry to the main bore. In order to further improve the reliability of the junction and the installation time, a new system would be required. After an evaluation period, the operator (Norsk Hydro) accepted a proposal from Sperry-Sun/ Halliburton to further develop their existing prototype Isolated Tie-Back System for use on Troll Olje. ITBS™ will provide both hydraulic and mechanical isolation, a combined flow area that is larger than that of the tubing above, and an acceptable solution for access to main bore and lateral. The long term objective was to install this TAML Level 5 system in less than six days. ITBS™ is a multilateral system based on a pre-milled window and on a latch coupling placed in the 9-5/8-in. liner section. After installation of screens in the main bore reservoir section, a whipstock is installed in the latch coupling and the window opened up to drill the lateral. To complete the well, the whipstock is retrieved and replaced by a deflector; and a multilateral junction system is then installed as an integral part of the lateral bore completion. The main component is a flexible hanger with D-shaped legs. This component is attached to the lateral liner on one leg and has a stinger on the other leg. The stinger is oriented and lands in a seal stack in the main bore deflector. On Troll Olje, screens are installed in both the main and lateral bore and the lateral liner is not cemented across the junction. An early prototype of the system was developed in 1998/99. The system was then further developed during 2000 and the first installation conducted for Norsk Hydro in the Troll Olje field in Norway. This paper will discuss the development of the ITBS™ system and also the first installation from a floating rig in the Troll Olje field. Introduction The Troll Olje Field is located approximately 100 km north west of Bergen, in the Norwegian Sector of the North Sea. The water depth is 315 – 340m. Troll Olje is part of the Troll gas field in which Norsk Hydro is responsible for development of two areas of a thin oil rim: the Troll Olje Oil Province (22 - 26m oil zone) and Troll Olje Gas Province (around 13m oil zone). The combined development is estimated to recover a total 1.33 billion barrels of oil. By March 2001, a total of 70 wells had been drilled and completed on the Troll Olje Field, including five multilateral wells. The wells are tied-in to one of the two floating production platforms - Troll B and Troll C. The multilateral well concept has been introduced on Troll Olje primarily to increase the total drainage area from the existing sub-sea template structures. Further development of Troll Olje includes another 20 multilateral wells. These multilateral wells contribute additional reserves in the region of 75 million barrels of oil. Drilling all these targets with conventional horizontal wells would not be practical. An alternative solution with four wellhead templates (16 slots) would contribute about 25 million barrels of oil less than the multilateral solution and also add greatly to the development costs.
As the industry continues to expand into ultradeepwater plays, an increasing number of tight tolerance wells warrant the use of an efficient system for determining early influxes or losses during drilling, tripping, and cementing operations. The narrow mud weight window for the majority of these wells requires an advanced solution in order to operate in all such conditions without compromising on safety. This paper describes a new early detection flow monitoring system and setup for floating rigs, and presents its application via a case study of a very high-profile ultra deepwater well. Good well surveillance for floating rigs requires precise measurements combined with an efficient smart process adapted to deepwater conditions in order to raise a reliable alarm in any condition, while minimizing the risk of false alarms. Careful sensor selection and sizing, together with particular attention to installation is required in order to achieve this degree of accuracy for all the drilling phases. The solution described in this case study provides drilling surveillance for all hole sizes, with flow up to 2000 gpm for accurate and early detection, and significantly increased safety during drilling, tripping, and cementing operations. This case study describes how kicks can be detected with a high degree of reliability much earlier than with the standard pit volume and flow paddle monitoring. In addition to this, it has shown its value by characterizing, in real time, the consequences following a packoff event and also by differentiating between a wash out and pump failure. Crew confidence in this detection system rapidly led to modifications of the operational procedures. For instance, flow checks were previously done for every pipe connection, taking up expensive rig time. Due to results obtained in the previous hole sections, the drilling procedures were updated in order to significantly reduce time spent flow-checking, while still maintaining maximum safety during the operations.
This paper describes the preparation and operation for the first use of a riserless mud recovery (RMR) system on the top-hole section of a well in the Gulf of Mexico. The material includes pre-well engineering and preparations including hydraulic analysis, pre-job vessel inspection, construction of new equipment, installation, pre-well planning decisions, and rationale for decisions. In addition also discussed are benefits including improved wellbore quality due to use of an engineered drilling fluid, logistics savings from reduction of drilling fluids, and minimized environmental impact. The paper also includes descriptions of equipment installation and testing onboard the drilling vessel operations during drilling, problems encountered and lessons learned from the operation. A description of all equipment is included in the paper along with specifications and operation parameters. An RMR system has application in the top-hole drilling of oil and gas wells. Using conventional methods, drilling fluid pumped down the drillstring during operations flows out onto the sea floor; this is often referred to as " Pump and Dump??. RMR collects the mud at the mud line and pumps the fluid back to the rig where it is reconditioned and reused. It allows the use of engineered drilling fluids and has possible applications for all offshore drilling. RMR was deployed on a dynamically positioned vessel, and successfully used to drill the 26-in. hole section. Drilling fluid recovered from the mud line back to the drillship was processed and reused, resulting in significant reduction in the volume of mud required for this top-hole section. RMR reduced costs through savings in drilling fluid and improved well construction. RMR is applicable to the drilling of top-holes in the entire Gulf of Mexico. It has significant potential to reduce top-hole drilling costs, eliminate casing stings, extend casing shoe depths, drill through and past problem formations and improve the wellbore by eliminating washouts and shallow hazards. Introduction Operators continue to explore and develop fields at increasing water depths. In certain offshore areas where younger sedimentary rocks are deposited, there is often a very narrow margin between formation pore pressure and fracture pressure that creates tremendous drilling challenges (Rocha and Bourgoyne, 1994). The solution to this narrow operating window is to develop techniques that extend the casing setting depths more efficiently. The use of a riserless drilling technique, dynamic kill drilling (DKD), has been instrumental in successfully pushing the casing depths deeper in deepwater applications (Johnson and Rowden, 2001). The DKD methodology employs the dual gradient drilling concept, consisting of the seawater hydrostatic above the mud line with the ability to vary the hydrostatic below the mud line by drilling fluid weight variations. This functional control of the drilling fluid density is tremendously advantageous while drilling shallow gas or water flows from over-pressured formations where large washouts, caves, formation compaction, and collapse could occur (Pelletier et al., 1999). This technique has been repeatedly employed in challenging deepwater projects where the initial upper hole sections were extended to obtain the required leak-off tests (LOTs).
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractNorsk Hydro has been installing multilateral wells for 10 years. By the end of March 2006, a total of 64 multilateral junctions were installed. The vast majority have been sealed TAML level 5 junctions constructed from floating vessels, primarily on the Troll West field. Hydro identified early multilateral wells as a key technology to enhance the oil recovery from the Troll West field. In 1995, a multilateral technology vendor was selected as supplier of multilateral systems. The close cooperation between Hydro and the multilateral technology vendor has been the key to the development of new multilateral systems and system variants to meet new requirements for the implementation of this emerging technology. This paper will briefly describe the development of the FlexRite® system and the subsequent variants like FlexRite® Intelligent Completion Interface and ReFlexRite®. Field operations involving these systems will be discussed, and the use of multilateral wells on Troll West will be presented in some detail with respect to; statistics for junctions installed by March 2006, presentation of example wells and economic effects from the use of multilateral wells.
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