Openhole sidetracking is most commonly applied in three drilling scenarios: 1) to drill a horizontal lateral from the main wellbore in unconventional reservoir exploration 2) to drill lateral in a multilateral well 3) to detour around a stuck fish. In most drilling operations, the risk and the economics associated with openhole sidetracking dictates that all commercially available methods and technologies be evaluated thoroughly to achieve the objective and re-establish normal drilling operations. The evaluation is more challenging in medium to hard formations or in highly deviated wells or a combination of both. Recently, the most requested application for the system has been for exploratory wells drilled in unconventional reservoir plays that are recent developments where little or no offset well data exists. In such fields there is significant risk in drilling a horizontal lateral because reservoir characteristics are not well known. The logical step therefore is to rely on the conventional methodology or on the historical experience of field engineers working the region. Traditionally, the predominant openhole sidetracking methodology started with setting a cement plug followed by a directional BHA once the cement hardens. The success of the plug setting operation depends on formation compressive strength, degree of downhole temperature/pressure, wellbore deviation, cement plug depth, quality of cement and cure time. The consequences of plug failure are extra trip time, a new cement plug, loss of drilling days and reconfiguration of drilling trajectory. A recent R&D effort has identified a new method and associated tools that can be effectively utilized to increase operational reliability in openhole sidetracking and to save costs in terms of time and materials.Single trip retrievable openhole sidetrack system: The system is designed for multilateral wells where access to the main bore is a requirement. The system is equally applicable in situations where cement plugs are ineffective such as in medium to hard formation or in highly deviated holes. No cementing operation is required.Cementing openhole system with anchor: The system is designed for unconventional reservoir exploration where the bottom hole is required to be plugged with cement once the pay zone has been identified and kick-off point for a lateral is confirmed. With the anchor firmly holding the system in place, the operator does not have to wait until the cement is fully cured. The solid ramp encased in the cement is used for sidetracking.Cementing openhole system without anchor. This system is designed for wells where there is a hard bottom available. The cement holds the system firmly at the bottom while a solid ramp encased in the cement is used for sidetracking purpose. The paper discusses mechanical and operational features of above system along with their respective field performances. The paper will also describe challenges faced in field runs, how those were overcome, the lesson learned and potential system modifications.
Many offshore oil fields throughout the world are reaching the end of their productive lives. Consequently, the operators are poised to plug and abandon a substantial number of wells in the next few years. This proliferation of current and future needs however present unique challenges for the operators and for the offshore service companies. The challenges requiring the most deliberation include:Partial plug & abandonment: A permanent abandonment of the bottom of the well and drilling new well from the upper section to access more productive targets allowing continued use of the existing platform infrastructure. The practice is known as slot recovery program.Requirements of local regulatory agencies: The steps required to qualify the offshore wells as permanently abandoned vary widely with the local regulatory jurisdiction. The governing bodies of the North Sea and Gulf of Mexico are good examples of slightly varying requirements for well abandonment.Combining safety and economics in meeting above two challenges. To meet these challenges, the offshore service companies have worked with the operators in developing innovative technical solutions that are economically viable and safety compliant. For Norwegian sector of the North Sea, a single trip casing cutting and pulling system has been developed and tested which provides multiple cuts capability and selective activation of heavy duty spear to overcome frictional resistance between casing and the cement or barite. A casing jack capable of pulling a million pounds of casing has been developed in case a need arises. Also a system designed to mill 150 meters of casing section is currently under field tests. For the Gulf of Mexico, a hydraulically activated tool to cut up to 72 inch casing has been developed. Also a single trip cut and pull system has been in operation for wells in deep waters. The system eliminates the need to strip the workstring/BHA equipment once the cut casing is at the surface. The authors will discuss these technical solutions in terms of new tools and procedures. Also discussed will be field data, lesson learned, planned improvements. Introduction The decision to plug and abandon (P & A) a well is strictly based on the economics. Once the production rate has fallen off to a level where operating expenses are higher than operating income, the well becomes a prime candidate for permanent abandonment. In other instances, only the bottom of the well is permanently abandoned and a sidetracked well is planned from the upper portion of the well to access a new target. This way the top infrastructure can be used again which makes this approach an economically attractive proposition particularly for offshore platforms where multiple wells are drilled and/or producing from a single platform structure. This methodology is known as slot recovery procedure. Only the lower section of the well is permanently abandoned. The upper section is used in accessing a new target by sidetracking the well. test
Historically, the profile of the window milled with a conventional whipstock system resembles an inverted tear drop shape. The resulting full gage window opening is relatively cramped for subsequent drilling assemblies and liner completions. For example, in 7" casing the total window opening is usually 10 feet long out of which only about 2 feet of the opening has full diameter access for drilling and completion tools. This paper presents a unique whipstock design and milling tool design, the combined performance of which produces a full gage window opening of up to 85% of the total window length and thereby provides an abundant clearance for drilling assemblies and liner completions. Test conducted on 7"-29 lbs./ft. casing resulted in a total window opening of 9.8 feet (118") out of which 7.5 feet (90") was a full gage 6.00" opening. Test on 9–5/8"-47 lbs./ft. casing produced 16.83 feet (202") total window length of which 14.50 feet (174") of the opening measured full gage width of 8.50". The whipstock can easily be modified to produce the desired length of full gage opening. Optionally, the window can be milled without the need for drilling a rat hole. The benefits of a longer full gage window aretrouble free entries and re-entries through the window for drilling and completion of lateral,ideal for short radius departure,allows sidetracking in hard formation without drilling rat hole,compensates for any mismatch in depth tally calculations, andeliminates problems associated with skewed window (longer full gage window is vertically straight). The paper details the test set up, test results, photograph and profile of actual milled windows and summarizes field run results. Introduction The conventional whipstock systems, currently in use, require single or multiple trips downhole to mill an appropriate window for sidetracking the well. In all cases, the whipstock includes a 1–1/2 to 3 degree tapered ramp, the length of which varies from 8 ft. to 18 ft. depending upon the casing size and manufacturer. The face of the ramp incorporates a concave profile to facilitate the guiding of the milling tool. In multiple trip operations, a starter mill is used to make the initial cut out followed by a window/watermelon mill combination milling tool which usually finishes the window. In a single trip operation only one milling tool is used to complete the window. In either case, the profile of the window looks like an inverted tear drop as shown in (Fig. 1). This shape is produced by milling the window using a continuous, single angle whipface. The full gage opening required for the subsequent drilling assemblies is usually less than 25% of the total widow length. This relatively cramped opening becomes more hazardous due to the jagged edges of the window resulting from the rough downhole milling operation. The BHA and completion equipment, particularly the packers may get tangled and prematurely damaged. In many cases, it may require additional reaming trips with a watermelon mill to elongate and smooth out the window profile. The above described systems have been in use for many years. The design of the whip stock and the milling tools were derived from the earlier versions of remedial tools. Relatively shallow 1–1/2 to 3 degree tapered ramps on the whipstock face were designed to generate gradual milling torque on the casing and to minimize the damage to the whipstock. Different shape mills were designed and run to elongate and dress the window to reduce the damage to the drilling and completion components. However, there were no serious attempts made to completely alter the window profile to eliminate potential damage to other components while passing through the window until now.
Openhole sidetracking is most commonly applied in three drilling scenarios: 1) to drill a horizontal lateral from the main wellbore in unconventional reservoir exploration 2) to drill lateral in a multilateral well 3) to detour around a stuck fish. In most drilling operations, the risk and the economics associated with openhole sidetracking dictates that all commercially available methods and technologies be evaluated thoroughly to achieve the objective and re-establish normal drilling operations. The evaluation is more challenging in medium to hard formations or in highly deviated wells or a combination of both. Recently, the most requested application for the system has been for exploratory wells drilled in unconventional reservoir plays that are recent developments where little or no offset well data exists. In such fields there is significant risk in drilling a horizontal lateral because reservoir characteristics are not well known. The logical step therefore is to rely on the conventional methodology or on the historical experience of field engineers working the region. Traditionally, the predominant openhole sidetracking methodology started with setting a cement plug followed by a directional BHA once the cement hardens. The success of the plug setting operation depends on formation compressive strength, degree of downhole temperature/pressure, wellbore deviation, cement plug depth, quality of cement and cure time. The consequences of plug failure are extra trip time, a new cement plug, loss of drilling days and reconfiguration of drilling trajectory. A recent R&D effort has identified a new method and associated tools that can be effectively utilized to increase operational reliability in openhole sidetracking and to save costs in terms of time and materials. Single trip retrievable openhole sidetrack system:The system is designed for multilateral wells where access to the main bore is a requirement. The system is equally applicable in situations where cement plugs are ineffective such as in medium to hard formation or in highly deviated holes. No cementing operation is required.Cementing openhole system with anchor:The system is designed for unconventional reservoir exploration where the bottom hole is required to be plugged with cement once the pay zone has been identified and kick-off point for a lateral is confirmed. With the anchor firmly holding the system in place, the operator does not have to wait until the cement is fully cured. The solid ramp encased in the cement is used for sidetracking.Cementing openhole system without anchor.This system is designed for wells where there is a hard bottom available. The cement holds the system firmly at the bottom while a solid ramp encased in the cement is used for sidetracking purpose. The paper discusses mechanical and operational features of above system along with their respective field performances. The paper will also describe challenges faced in field runs, how those were overcome, the lesson learned and potential system modifications.
Conventional approach to deepwater reaming solutions generally consist of selecting appropriate size reaming tools, running hydraulic analysis for the interval and relying on the expertise of tool operator for the tool performance. This approach works in situations where the drilling environment is usually friendly and the target is relatively straight forward. However in today’s drilling environment, an operator may be faced with challenges associated with deeper water depth, deeper wellbores, tortuous drilling trajectories, higher pressures/temperatures and a variety of formations. These challenges cannot be successfully met head-on with the conventional methodology. This paper presents an innovative and focused approach to the deepwater reaming operations where all drilling and operational issues are analyzed and a comprehensive solution is developed that meets the challenges presented by the specific application. The analysis includes (1) selection and location of reaming tools based upon the dynamic simulation of the entire drill string (2) selection of cutting structure suitable for the interval and one that matches with the bit (3) selection of appropriate ream on demand control feature (4) hydraulic analysis of the reaming interval and (5) recommendations of operating parameters selected for mitigating vibrations during the reaming operation. This approach was made possible in recent times due to (a) advances in technologies, specifically the material technologies and the computing technologies which have been emerging at accelerated pace and (b) synergetic efforts between the drilling group, directional group and the analytical group within the organization. The authors will provide an overview of the features and system functionality and each of its critical components. This will include details about specific hardware and discussion of software analysis. Examples of actual field applications, results, lesson learned and discussion of the way forward activities will also be presented.
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