Instability regimes and self-excited vibrations in deep drilling systems

peer reviewe

State Dependent Delayed Drill-string Vibration : Theory, Experiments and New Model

L.J. Pei would like to acknowledge NNSF of China (No. 11372282) and China Scholarship Council.Peer reviewedPublisher PD

Hybrid Modelling and Optimisation of Oil Well Drillstrings

The failure of oil well drillstrings due to torsional and longitudinal stresses caused by stick-slip phenomena during the drilling operation causes great expense to industry. Due to the complicated and harsh drilling environment, modelling of the drillstring becomes an essential requirement in studies. Currently, this is achieved by modelling the drillstring as a torsional lumped model (which ignores the length of the drillstring) for real-time measurement and control. In this thesis, a distributed-lumped model including the effects of drillstring length was developed to represent the drillstring, and was used to simulate stick-slip vibration. The model was developed with increasing levels of detail and the resultant models were validated against typical measured signals from the published literature. The stick-slip model describes the friction model that exists between the cutting tool and the rock. Based on theoretical analysis and mathematical formulation an efficient and adaptable model was created which was then used in the application of a method of species conserving genetic algorithm (SCGA) to optimise the drilling parameters. In conclusion, it was shown that the distributed-lumped model showed improved detail in predicting the transient response and demonstrated the importance of including the drillstring length. Predicting the response of different parameters along the drillstring is now possible and this showed the significant effect of modelling the drillcollar. The model was shown to better represent real system and was therefore far more suited to use with real time measurements.Iraqi Government, Ministry of Higher Education and Scientific Research

Investigation of drillstring vibration reduction tools

Drilling related problems such as drillstring vibration is an important cause of premature failure of drillstring components and drilling inefficiency. The vibration of drillstring interferes with measurement collected while drilling. In severe cases, drillstring vibration will lead to wellbore instability that will result in an increase in the operation cost. In the late 1980\u27s, a lot of studies and techniques were developed to mitigate drillstring vibration and downhole vibration measurements were introduced to the industry in two forms; real time measurements and memory devices measurements A study of drillstring vibration of three different wells located in the Norwegian North Sea was analyzed. The bottom hole assembly (BHA) of two wells consisted of anti-vibration technology. The study involved a verification of anti stalling technology (AST) and V-stab vibration reduction tools. Part of the study illustrates the different in lateral vibration in different wells of matching lithology which include a statistical analysis of anti-vibration tools performance. Finally, a statistical analysis was conducted on downhole vibration measurement to investigate the sampling rate of the device. Alternating lithology has a big impact on lateral vibration; however, lateral vibration is not the same for different wells in the same formations due to the difference in the BHA assemblies. The study showed that lateral vibration using the V-stab was lower than the one using the AST tool. Considering torsional vibration, the analysis reveled that V-stab has a lower stick/slip severity than the AST tool. The field study showed that the roller-cone bit generates less torsional vibration than the PDC bit due to different cutting actions. One of the important findings was that there was no correlation between drillstring vibration and mechanical specific Energy (MSE) --Abstract, page iii

Torsional stick-slip vibrations and multistability in drill-strings

This is the final version. Available on open access from Elsevier via the DOI in this recordData accessibility: The datasets generated and analysed during the current study are available from the corresponding author on reasonable request.The generalized lumped-parameter model of the drill-string system is studied in this paper to provide a fundamental understanding of the torsional stick-slip vibrations in downhole drilling. Our investigation focuses on analysing the cause of three coexisting states: bit sticking, stick-slip vibration, and constant rotation. A critical region of multistability is identified based on the lumped-parameter model, and the conditions for switching between these multiple stable states are discussed. Special attention is given to the bifurcation structure of the considered drill-string model, which is obtained via path-following methods for nonsmooth dynamical systems. The bifurcation scenario is compared to the case when a longer drill-string is considered, which amounts to drilling deeper. It is found that the main features of the bifurcation picture persist under variation of the drill-string length, with certain numerical differences regarding for instance the window of multistability.Engineering and Physical Sciences Research Council (EPSRC)National Natural Science Foundation of ChinaChina Scholarship Counci

The effect of well path, tortuosity and drillstring design on the transmission of axial and torsional vibrations from the bit and mitigation control strategies

As well designs become increasingly complicated, a complete understanding of drillstring vibrations is key to maximize drilling efficiency, to reduce drillstring dysfunction and to minimize drillstring, tool, and borehole damage. Torque and drag models exist that seek to quantify the effects of borehole inclination and tortuosity on static friction along the drillstring; however, the effects on dynamic friction remains poorly understood. This dissertation begins with a review of the past fifty years of work on drillstring dynamics models, an overview of the proposed control strategies and a summary deployed vibration mitigation applications within the drilling industry. Derivations from first principles of a series of computationally efficient axial and torsional drillstring models in both the frequency and time domains are then presented and verified with field data. The transfer matrix approach is used to predict the severity of axial vibrations along the drillstring and is verified using a series of case studies using field data. Harmonic axial vibrations within drillstrings are either induced intentionally, in the case of axial oscillation tools midway along the drillstring, or unintentional, in the case of bit bounce. Two case studies of bit bounce are first evaluated to ensure model validity for a harmonic excitation at a the bit and the model is found to accurately predict bit bounce based on surface rotation rates. Induced axial oscillations, generated by axial oscillation tools, are then investigated to quantify friction reduction and drilling efficiency improvements. Optimal placement is found to depend on wellbore geometry, but is usually restricted to periodic regions of the drillstring. These optimizations are then verified using field trials and suggest that improved placement can result in 20% or more reduction in friction along the drillstring. Two applications of torsional drillstring vibrations are then investigated -- stick slip mitigation and drillstring imaging. The time domain form of the torsional drillstring model is used first to evaluate the effectiveness of three types of top drive controllers -- stiff controllers, tuned PI controllers and impedance matching controllers -- in mitigating stick slip oscillations. Then, the transfer matrix method is applied to evaluate the effect of wellbore geometry on drillstring mobility to conclude that higher order modes of stick slip may become dominant in non-vertical wellbores. The feasibility of drillstring imaging using torsional signals from surface is then investigated to identify inputs and methods that show promise in three setups of varying complexity -- a hanging beam, a laboratory drillstring model and a drilling rig. Two techniques show promise -- white noise injection and model fitting of a step response -- in identifying larger features, including drillstring length and BHA location. However, low sampling frequencies and low bandwidth inputs reduce the ability to image small features such as friction points along the wellpath.Petroleum and Geosystems Engineerin

Deep Drilling in the Highly Laminated Pinedale Anticline: Downhole Vibrations Study and Bit Dysfunction Diagnosis

Ultra Petroleum has been drilling in the Pinedale Anticline in Wyoming since 2003. At that point in time, wells could take as much as 75 days to reach target depth. In the first quarter of 2015, Ultra Petroleum, has greatly reduced their spud to target depth time to 9 days. However, despite their drastic improvement in performance over the years, Ultra’s current performance has seemed to have plateaued due to consistently occurring non-productive time on each well resulting from as many as three bit trips to replace damaged drill bits, while drilling the 6 inch production hole. Hours spent tripping in and out of the hole to replace worn drill bits is extremely costly. In the third quarter of 2014, Ultra in an effort to improve performance, began a concerted effort to target this problem area and improve performance. After training Ultra Petroleum personnel on a physics-based, continuous improvement set of practices, Ultra Petroleum’s performance increased significantly. In addition to the training, Ultra Petroleum and Texas A&M University examined their operations performance and practices using downhole drilling dynamics data. After the analysis, suggestions were made for engineering redesign possibilities. The objective of this study is to determine the in-situ dynamics state of the bottom hole assembly and drill bit, and how this excited vibrational state contributes to the bit damage seen from the drill bits pulled out of the well. This thesis will document that students work and findings. In order to accomplish this goal downhole dynamics measurements were studied to determine the specific vibrations present in the drilling of these wells. In addition these measurements were used to determining the severity of each vibration type and the effectiveness of specific drilling equipment at mitigating their negative effects on performance and tool life. Meaningful results were obtained from the downhole dynamics measurements that provide both knowledge to the operator and suggestions for ways to improve performance and tool life, and include conclusions regarding the effectiveness of roller reamers and depth of cut control bits in reducing torsional oscillation, the effectiveness of full-gauge stabilization and extended gauge bits at reducing lateral vibrations, and hypotheses about the effectiveness of incorporating some specific tools and techniques for performance improvement