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As offshore drilling grows more crowded and more complex, greater emphasis is placed on avoiding collisions with offset wellbores. The implications of a collision with an existing well are very real, and care must be taken to minimize the risks associated with such incidents. Collision with a producing well carries additional risks, including potential well-control situations and lost income from shut-in wells. With more wells being drilled from multi-well locations, well collision is becoming a very real possibility. Today's drilling trends toward more directional, horizontal, and fishbone multilateral wells, often with several from a single slot using subsea wellheads. This paper covers the practices for sidetracking out of the well using a whipstock and minimizing the risk of collision with offset wells. Special emphasis is placed on optimizing whipstock placement (orientation and depth), use of gyroscopic tools while milling and drilling ahead, and the use of traveling cylinders for collision avoidance. Case histories are presented here to illustrate the successful application of these techniques. Introduction With the worldwide growth in drilling activities, operators are encountering increasingly complex and crowded drilling, especially in developed fields where the existing well density is high. In recent years reentry drilling has become an increasingly popular option for production optimization. One of the important aspects of reentry is to mill a window in an existing casing. Many of the wells drilled in developed fields are sidetracking from the existing wellbore. These cased-hole sidetracks are performed using a whipstock assembly. After setting the whipstock assembly, a rathole is drilled to land the drilling bottomhole assembly (BHA) to drill the rest of the section. After exiting the whipstock window, the sidetrack well will be under the magnetic interference from the parent wellbore and nearby offset wells. Depending on the proximity of the offset wells, magnetic interference can impair conventional measurement while drilling (MWD) for a substantial drilled distance. Drilling blind after exiting the window may result in catastrophic results, including colliding with a nearby existing producing wellbore. This paper emphasizes the following:Practices on whipstock placement, orientation to avoid collision risks and optimization of directional drilling at the same timeReducing directional uncertainties by using gyro MWD and single/multishot gyro tools while drilling close to the offsets wellsAnticollision management using traveling cylinder plot and spider plot
As offshore drilling grows more crowded and more complex, greater emphasis is placed on avoiding collisions with offset wellbores. The implications of a collision with an existing well are very real, and care must be taken to minimize the risks associated with such incidents. Collision with a producing well carries additional risks, including potential well-control situations and lost income from shut-in wells. With more wells being drilled from multi-well locations, well collision is becoming a very real possibility. Today's drilling trends toward more directional, horizontal, and fishbone multilateral wells, often with several from a single slot using subsea wellheads. This paper covers the practices for sidetracking out of the well using a whipstock and minimizing the risk of collision with offset wells. Special emphasis is placed on optimizing whipstock placement (orientation and depth), use of gyroscopic tools while milling and drilling ahead, and the use of traveling cylinders for collision avoidance. Case histories are presented here to illustrate the successful application of these techniques. Introduction With the worldwide growth in drilling activities, operators are encountering increasingly complex and crowded drilling, especially in developed fields where the existing well density is high. In recent years reentry drilling has become an increasingly popular option for production optimization. One of the important aspects of reentry is to mill a window in an existing casing. Many of the wells drilled in developed fields are sidetracking from the existing wellbore. These cased-hole sidetracks are performed using a whipstock assembly. After setting the whipstock assembly, a rathole is drilled to land the drilling bottomhole assembly (BHA) to drill the rest of the section. After exiting the whipstock window, the sidetrack well will be under the magnetic interference from the parent wellbore and nearby offset wells. Depending on the proximity of the offset wells, magnetic interference can impair conventional measurement while drilling (MWD) for a substantial drilled distance. Drilling blind after exiting the window may result in catastrophic results, including colliding with a nearby existing producing wellbore. This paper emphasizes the following:Practices on whipstock placement, orientation to avoid collision risks and optimization of directional drilling at the same timeReducing directional uncertainties by using gyro MWD and single/multishot gyro tools while drilling close to the offsets wellsAnticollision management using traveling cylinder plot and spider plot
Maximizing profitability in mature fields is dependent on reducing drilling and operational expenses to maintain optimized hydrocarbon production. As Forties field UK North Sea matures, drilling challenges are becoming increasingly more difficult and complex. Wellbore instability caused by the loss of reservoir pressure and anisotropic properties of overburden shale is a major issue as targets are pushed further away from the platform. To continue successful development of Forties field, the operator is required to drill high-inclination deviated wellbores sidetracked from existing boreholes. The unstable shale outside of the sidetrack window requires a low-side casing exit. To optimize operations the sidetrack must be completed on the first attempt. When a first sidetrack fails, a second is often initiated approximately 10m (or interval thereof) further up in the wellbore with a higher mud weight. Unable to get more than a few feet away from the original wellbore within such a short distance, the new sidetrack can frequently re-enter the zone already damaged by the previous attempt and again runs into trouble. This broken formation becomes even more destabilized with increased mud weight. To solve the operational / economic challenges, a unique wellbore departure system was developed to deliver fast, high-quality windows and sidetracks tailored specifically to meet operator’s low-side application objectives without compromising performance. The low-side exit requires a unique set of pre-job equipment modifications which is performed in the service provider’s workshop prior to shipping equipment to the well-site. The modification allows an upward force to be exerted at the tip of the whip face on setting the permanent packer / anchor thereby overcoming the natural gravitational forces. This upward force does not come into effect until the packer is energized, thus ensuring the whipstock assembly remains flexible enough to mitigate wellbore tortuosity encountered whilst running in the hole. The system was successfully applied initially on three challenging uncemented whipstock sidetracks with single-trip window success (up to 77° inclination / 180° orientation). On all three jobs the anchoring and milling technology worked flawlessly with no issues when subsequently tripping directional BHA or liners through the window. Application engineers performed pre / post-job briefings with service provider’s rig site / offshore supervisors to ensure specific low-side exit guidelines were followed and that lessons learned or suggestions for improvement were captured and documented for prosperity. The authors will present Forties field case studies that document procedural repeatability and how the tools and techniques could be used for any challenging low-side uncemented casing exits.
Innovative materials technology advances sidetracking capabilities and offers a cost-effective approach to creating multiple laterals from the same mother bore. The key component to this sidetracking system is a mill designed with polycrystalline diamond (PCD) inserts. Current technology dictates that sidetrack milling be performed with mills dressed with crushed or pre-formed tungsten carbide that is manually applied. Regardless of technology, the success of the sidetrack is dependent upon on the skill and experience of the welder to properly dress the mill. The PCD mill eliminates the dressing process and the related performance uncertainties. This paper discusses how PCD cutters, which are commonly used in drilling, were modified and applied to a casing-sidetracking mnill. The mill design capitalizes on their ability to effectively and swiftly cut a window in the casing and drill a rat hole in formations with compressive strengths of up to 40,000 psi. The benefits of such a mill are:using the same cutting element for both steel and hard formations,substantial cost savings when constructing multiple laterals from the same mother bore,increased consistency in mill manufacture,reliable milling performance andimproved efficiency in the sidetracking operation. This paper profiles the development and testing from concept to a field-proven tool. The paper details:laboratory-milling tests that identify the best material for cutting steels,Oklahoma field tests in 9–5/8 in. casing to verify the feasibility of PCD casing milling and formation drilling,West Texas and Colombia field runs in operators' 7 and 9–5/8 in. casing to mill a window and drill hard formations. Additionally, the paper will elaborate on the future potential of integrating this technology to a directional drilling assembly to drill laterals with the same equipment and preferably in the same trip for short laterals. Introduction The individual performance of mills used to cut a casing window and sidetracking a well can differ widely. This is due to varying downhole conditions, operating parameters and applications.1 Properly managed quality and process controls, instituted for the manufacturing of milling tools, are essential for consistent performance. Current technology dictates that casing sidetracking mills are dressed with crushed tungsten carbide and/or pre-formed tungsten carbide. It is this cutter dressing that is the cutting structure responsible for removing steel and formation. The dressing must be able to withstand the diverse grades and weights of casing and the varying hardness and abrasiveness of the rat hole formations. The dressing process requirements for successful manual application of the crushed and pre-formed tungsten carbide are very demanding. The quality of the process is dependent upon the skill of the applicator or welder. The consistency of the application is paramount to the success of the mill. Sidetracking mills must adhere to critical design criteria. For this reason, elimination of the often difficult and usually inconsistent dressing process and potential performance uncertainties is preferred. Sidetracking Synergy In light of the irregularities that have been associated with conventional sidetracking mills, the concept of using PCD inserts in place of conventional cutting structures for casing sidetracking was developed. Utilizing PCD inserts as the cutting structure could potentially increase consistency in product manufacturing and performance. The cylindrical PCD cutting elements would be precisely placed in the cutting structure of the PCD Mills. The PCD Mill could deliver a much more reliable milling performance and overall improved efficiency in the sidetracking operation, because it would no longer have to rely on the labor-intensive process of correctly or specifically applying crushed and/or pre-formed tungsten carbide.
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