The understanding and mitigation of downhole vibration has been the subject of intense scientific research in the drilling industry in recent years, as inefficient drilling results in slower and more expensive operations. In order to drill ahead, a sufficient amount of energy must be supplied by the rig to overcome the rock strength, the reactive torque of the drilling system, drag forces, fluid pressure losses, as well as the energy lost by way of downhole vibrations. It has been well documented that downhole vibrations are a significant drain on the amount of effective drilling energy available to the bit. When the drill string enters resonant modes of vibration, not only does the drilling efficiency decrease, but the likelihood of catastrophic drill string component failures increase. The amount of destructive energy expended in these resonant modes of vibration, when left unchecked, may overcome the material limits of components in the drill string. In this sense, the mitigation of downhole vibrations will result in faster, smoother, and cheaper drilling operations. Software using Finite Element Analysis (FEA) has been developed to understand these vibration phenomena and to predict which combinations of drilling parameters should result in more efficient drilling. The software graphically presents the results, depicting undesired levels of resonant vibration produced with specific drilling parameter combinations, based on the BHA geometry and wellbore design. Predictions made by this software have produced notable results, including a world record for Rate of Penetration (ROP) in the Gulf of Mexico. This paper also examines different Bottom Hole Assembly (BHA) designs and the resonant vibration modes that may be initiated while drilling, using the proprietary software package. The combination of proper BHA design and the correct selection of parameters results an overall improvement to drilling efficiency. A variety of case studies from Latin America, incorporating the results of the vibration analysis, will demonstrate solid improvements to drilling operations in terms of time and cost savings, increased penetration rates, and improved dull conditions. The use of field validated software for vibration prediction and mitigation has a potential role in the drilling industry as important as the introduction of PDC bits in the 1980s.
Major performance challenges for deepwater applications from a drill bit standpoint were identified as (1) High surface torque in salt is one of the major ROP limiters. (2) Inability to control depth of cut in soft rocks including shale and salt and when drilling in interbedded formations results in torsional oscillations and stick-slip. (3) Improper combination of bit and reamer induces drillstring vibrations. This paper presents the development of new drill bit technologies combined with a new system matching analysis package to address those problems. Salt mechanical behavior was evaluated using triaxial testing under confining pressures up to 5,000 psi. Full scale pressurized testing was then conducted to evaluate salt drilling behavior versus rock characteristics. The following specific challenges were addressed: Non-planar PDC geometries were tested in salt, among other rocks, to identify a geometry which results in maximum increase in ROP at any given torque.New insert shapes were developed and tested for more effective and accurate depth of control.A full drillstring analysis model was developed with the ability to predict downhole and surface torque and WOB as well as drillstring dynamics, torque, and drag. The new shaped cutter full scale pressurized test resulted in an increase in ROP/torque ratio throughout the different rock and a 28% increase in salt. The cutter also increased ROP/WOB ratio by 42%. Furthermore, the new insert shapes proved to be more effective in controlling depth of cut, resulting in an extra 35% reduction in torque/WOB ratio compared to standard insert shapes. The project is now in field evaluation and the new drill string analysis tool has been applied to several field applications including some in the Middle East, North Sea, Gulf of Mexico, and the Caribbean for different purposes. Some of those purposes include buttonhole assempbly (BHA) selection for given bit and reamer, bit selection for a given BHA design and reamer, and drilling parameter optimization for a given BHA design, bit, and reamer. New insert shapes were run in multiple applications in North America, including in North Dakota and Oklahoma, with promising results proving that although the project was focused on deepwater drilling challenges, the novel solutions are applicable to a wide range of applications.
TX 75083-3836 U.S.A., fax 1.972.952.9435. AbstractThe oil industry is increasingly interested in drilling dynamics as a primary cause of drilling inefficiency. It has become ever more important to be able to both accurately predict and detect downhole vibration/instability throughout the entire drill string. The drill bit is often assigned as the cause, and frequently bears the scars of dynamic drilling problems. Historically bit manufacturers have used a combination of dull grades and surface data to speculate on cause and effect of downhole events with insufficient attention to what may be occurring in between.A small vibration logging tool has been employed in hundreds of applications worldwide. This paper discusses the implementation of this device and its flexibility for placement of multiple tools in various locations, such as specific built subs and/or existing tools, within the drillstring. The versatility of this tool design offers the possibility to be run with any type of bit, fixed cutter or roller cone, regardless of manufacturer thus making it transparent to drilling operations throughout the entire drilling assembly.Specific field cases will be presented including; validation of pre-run dynamics modeling software, rotary steerable tools, concentric and eccentric hole opening tools, and response of different BHA configurations. This type of data is important to further the understanding of drill bit, drillstring component, and overall drillstring dynamic performance.
Software systems are developed with the intent of providing methods to perform specific business tasks. However, in actual use cases, additional human processes or supplemental software are often required to complete the business process. In ideal cases, the software would guide the user through the entire business process and significantly aid in the required decision making or analysis to complete the process. This paper will present the development of a new drilling optimization software system ergonomically modeled on key business and analytical processes. These key processes have been organically developed over a number of years for a commercial drilling optimization service using data from downhole drilling dynamics recorders. A multi-disciplinary project team including business unit managers, project coordinators, data analysts, software architects and developers was assembled. The project team designed the new system to ensure it would fit the human processes that had historically been used to support the commercial service. The new system models all of the key business processes associated with the commercial drilling optimization service. These processes include job setup, mobilization of tools, assignment of field personnel to the job, acquisition of all required data in the field, and reporting tools for field personnel. The system also provides the user with an intuitive suite of data analysis and drilling optimization techniques. These include automated processes for handling, merging, analyzing, and presenting the surface drilling parameters and recorded downhole drilling dynamics data. Additionally, the user is provided with recommended data analysis and optimization routines from the system based on data entered throughout the business processes from job setup to field operations and based on trends identified in the surface parameters and recorded downhole drilling dynamics data imported into the system. Case studies demonstrating the value-added to the users of the new system will be presented.
Resonance is the tendency of a system to oscillate with greater amplitude at specific frequencies. When present in the downhole environment, this effect limits drilling performance. Often, this issue is resolved by employing Finite Element Analysis (FEA) to predict the critical or natural frequencies, which is validated by observing increased vibration levels when rotating at a critical speed. However, this approach is based solely on circumstantial evidence and does not confirm the vibration is occurring at the predicted frequency.By using multiple Downhole Dynamics Data Recorders (DDDR) in a Bottom Hole Assembly (BHA), the actual vibration frequencies occurring downhole can be calculated and compared to predicted frequencies, thereby validating the FEA model. This technique was recently used to identify the cause of recurring over-torqued connections in a deepwater application. Analysis of the DDDR data, alongside critical speed modeling, revealed that isolated vibrations within the drill collars were allowing connections to work themselves tighter during specific drilling intervals. These measured vibrations were shown to be resonance-induced by matching predicted natural frequencies with the calculated frequencies from the DDDR, where the observed vibrations increased and decreased in magnitude as the rotation corresponded to the modeled frequencies.The innovative visualization of downhole vibration data and the validation of critical speed modeling techniques provide a step forward in drilling assembly optimization efforts. These findings will improve the industry's understanding of critical speed modeling, which in turn will illuminate potential shortcomings of the current methods of vibration mitigation. Practitioners will now be able to design BHAs with more confidence in the results of specific modeling principles, which will ultimately improve performance, reliability and efficiency by eliminating harmful dynamic behaviors.
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