The evolution of multilateral technology has created a large variation in completion styles for multilateral wells. Many of the methods are simple and basic while others are much more complex. These complex completions allow the use of multilaterals in a much wider range of well scenarios but they also create a new array of obstacles, concerns and risks. This paper will outline and categorize the various multilateral options that have emerged and the advantages and disadvantages of each. In addition, the reservoir and production parameters that influence the final multilateral completion choice will be discussed. Introduction Multilateral wells in their most simple form have been utilized in the oil and gas industry since the 1950's. These early multilateral systems, however, were only suitable in their application to a small segment of wells. Fortunately, over the last few years, drilling and completion techniques have improved to the point that an ever increasing variety of wells can now be completed as a multilateral. The challenge is becoming a question not of whether a multilateral system is available, but rather a question of what type of multilateral, if any, is best suited to the reservoir and production demands. When considering a multilateral completion, five parameters merit particular attention: Reservoir Suitability. The goal of the multilateral system is to maximize production from the reservoir with a minimum increase in drilling and completion costs. This requirement can be satisfied in one of two ways:The multilateral can be constructed with all production bores located in a single producing formation. This allows an optimized drainage pattern, greater fracture exposure, and a decreased probability of water or gas coning due to drawdown.The multilateral can be completed with the production bores located in separate producing formations. This allows marginal formations to be produced that otherwise could not be economically completed. In most cases, a multilateral well will cost more to construct than a single vertical or horizontal bore. Economic benefits will be derived primarily from increased production and/or reserves. To ensure such benefits, it is vitally important to have a thorough knowledge and understanding of the reservoir mechanics, and to use that knowledge and understanding to design multilateral completions from the reservoir up. Formation Characteristics at the Lateral Bore Kick-Off Junctions. As with conventional wells, the wellbore stability must be considered when choosing whether or not to case the hole. In addition, with a multilateral system, the geology at the junction of the lateral bores must also be closely scrutinized. The most flexible multilateral completions are those designed with the junction kick-off point located in a strong, competent, consolidated formation. However, if geology or other downhole conditions preclude this ideal scenario, mechanical support and, perhaps, hydraulic isolation must be included as part of the completion design. Differential Pressure at the Junction. Even if the lateral junction is initially competent, the completion design must take into consideration how the formation will respond as the well is produced and pressure drawdown occurs. It is not enough to just provide support during the initial few months of the well production; multilaterals must be designed for the life of the well. If the junction formation cannot retain its integrity as pressure drawdown occurs, hydraulic isolation of the junction may need to be considered. Production Mechanics. Production mechanics, as well as regulatory and environmental requirements, exert strong influence on multilateral completion design, particularly as regards zonal isolation. Any of these factors, either individually or in combination, may necessitate isolated, dual-string production to surface when the production is from multiple reservoirs. On the other hand, casing and tubular sizing and uphole equipment needs often dictate that production be commingled at the lateral junction and produced up a single string. P. 215^
In order to access additional reservoir, Hocol S.A. recently sidetracked out of a well located in the Ocelote Field, Colombia. The optimum path for the new well trajectory required exiting from the low side of the cased mainbore in a horizontal section of the existing well. Additionally, the proposed drilling assembly would utilize a Rotary Steerable System (RSS) in order to best reach target reservoir. Both of these requirements created additional challenges to the operator when designing a reliable casing exit operation. The RSS, which requires rotation along the length of the drill pipe, created concern due to the sidewall loading forces at the junction point which could have potentially impeded both downhole bit performance and drill pipe life. Meanwhile the desire for a low side casing exit in a horizontal wellbore generated concern that gravity would enable the whipstock to sag towards the low side of the casing and potentially interfere with drilling assembly trips through the window and into the lateral open hole. The operator sought out solutions that addressed both of the issues while still providing field proven casing exit techniques. The technology ultimately selected by the operator involved a casing exit system with a longer whipstock face therefore providing a longer casing exit window and reduced dog leg severity through the junction area. Additionally, the chosen whipstock system provided a patented "fulcrum design" to actively lock the whipstock assembly against the casing wall and away from the low side casing window in horizontal installations. This paper provides background information on the Ocelote Field and the drivers behind this sidetracking project. The design and operational challenges created by the desired drilling program are discussed along with a further description of the specific design problems encountered including the chosen installation equipment and techniques that addressed these challenges. Finally, the actual installation process along with problems encountered and successes achieved is covered.
Extended reach and highly deviated wellbores are becoming more and more commonplace in the oil and gas industry, bringing with them a host of challenges related to many aspects of the well construction process. Multilateral wells are an excellent example of this situation due to the doglegs formed when milling and drilling side tracks, the deviation of the hole, and the necessity of getting equipment to bottom and setting weight down to set and operate that equipment, especially during casing exits. Advanced technology has been developed to drill multilateral wells, but even this equipment can run up against its limitations in extremely challenging wells as operators continue to push the technology envelope. It is in these scenarios that combining technologies can provide the solution to safely and successfully manage downhole operations like casing exits and the drilling and completion of multilateral and extended reach wells. Such technology combinations can have a significant effect, not only on the ability to achieve far reaching targets, but also on the well construction time required and therefore the overall operational costs. In this paper the authors will focus on the combination of technologies to create multilateral wells in Extended Reach Well (ERW) scenarios where excessive torque and drag effects can adversely impact: Torque and weight while milling – associated with sidetracks through cased hole.Getting tools to target depth.Getting the loads at depth that are required to activate, set or release equipment downhole. They will review a hollow whipstock multilateral system and sub-based torque and drag reduction tools and present case studies of wells drilled successfully with these technologies, including the creation of the worlds’ deepest known horizontal casing exit.
This paper will detail a recent four-well TAML Level 4 multilateral (ML) installation in a field located offshore Thailand. The drivers that led the operator to seek out a first time multilateral solution for this field development will be covered, along with the variables considered in selecting the specific multilateral system that was ultimately chosen. Both the difficulties encountered and the successes achieved during the multilateral planning, installation and perforating processes will be covered.Although ultimately successful in all four wells, the multilateral construction process was not without challenges. The shallow depths of the multilateral junctions and the resulting weak formations resulted in a need for maximum mechanical support at the junction. At the same time, the multilateral needed to use a minimum of specialized equipment and processes to meet the timing urgency resulting from the existing rig availability deadline. This short timing made equipment and personnel sourcing a vital factor in the eventual success of the project. The importation of the perforating charges that are used in this ML system was especially challenging and must be taken into greater consideration when planning future installations.At the end of the project, the success of the installations was due in large part to the simplicity and reliability of the ML systems used, but another key factor in the success was the necessary and careful coordination of planning and activities between the operator and the service company providers involved in the multilateral construction process. The historical perception in the petroleum industry has often assumed that multilaterals require extensive lead times and that operating companies without previous multilateral experience face a steep learning curve to achieve successful results. The success of this project, however, demonstrates that today's multilaterals can be reliable and simple enough to consider even when time requirements are tight and in areas where multilaterals are considered a ЉnewerЉ technology.
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