Design and analysis of robust controllers for directional drilling tools

Directional drilling is a very important tool for the development of oil and gas deposits. Attitude control which enables directional drilling for the efficient placement of the directional drilling tools in petroleum producing zones is reviewed along with the various engineering requirements or constraints. This thesis explores a multivariable attitude governing plant model as formulated in Panchal et al. (2010) which is used for developing robust control techniques. An inherent input and measurement delay which accounts for the plant's dead-time is included in the design of the controllers. A Smith Predictor controller is developed for reducing the effect of this dead-time. The developed controllers are compared for performance and robustness using structured singular value analysis and also for their performance indicated by the transient response of the closed loop models. Results for the transient non-linear simulation of the proposed controllers are also presented. The results obtained indicate that the objectives are satisfactorily achieved

Applying a modified Smith predictor-bilinear proportional plus integral control for directional drilling

Recently, a Bilinear Proportional plus Integral (BPI) controller was proposed for the control of directional drilling tools commonly used in the oil industry However, there are delays in the measurement signals which reduces the system performance. Here, the BPI controller is extended by addition of a modified Smith predictor. The effectiveness, robustness and stability of the proposed modified Smith Predictor (SP)-BPI controller are analysed. Transient simulations are presented and compared with that of the earlier BPI controller. From the results, it can be surmised that the proposed modified SP-BPI controller significantly reduces the adverse effects of disturbances and time delay on the feedback measurements with respect to stability and performance of the directional drilling tool

Path optimization advisory and analytical tools for directional drilling

In directional drilling, well positioning and drilling instructions are planned based on human experiences and may require excessive computation and drilling times. Directional drilling process nowadays lacks optimization and automation to improve performance and efficiency. A path optimization advisor is developed with novel cost analysis, to support real-time directional drilling decisions. Spline in tension is used to simulated drilling path in the path optimization algorithms; more accurate and convenient for optimization purposes than commonly used survey calculation methods. The best valued path is solved using multi-loop optimization process, by determining the path with the lowest accumulated cost. Costs specified for each section are formulated and transformed into equal units. Actual drilling instruction is fitted to the optimal path with consideration of motor tendency and capabilities. The advisor developed using Matlab is validated that such a system can be used in real time directional drilling environments, to provide suggestions. Test cases using simulated drilling situation and historical data are tested for resulting instruction validation. Produced instruction and path results proved to be realistic and optimized based on specified cost functions. Comparing the optimized path with actual drilling instruction and survey drilled in historical cases, plan suggested by the path optimization advisor provides a better valued correction path.Petroleum and Geosystems Engineerin

Deep borehole disposal of nuclear waste: US perspective

Radioactive waste disposal in deep boreholes may be more "ready" than disposal in mined geologic repositories since mankind has greater experience operating small deep holes - boreholes, than big shallow holes - mines. There are several thousand precedents for constructing >2 km deep boreholes and several hundred precedents for disposing long-lived wastes in boreholes. Borehole disposal is likely to be faster, cheaper, and more flexible than mined disposal, while also offering greater long-term isolation. Isolation would rely on the great depth, water density gradients, and reducing conditions to prevent vertical movement of waste up the borehole.Comment: 24 pages, 8 figure

Making risk-informed decisions to optimize drilling operations using along string measurements with Wired drill pipe a high-speed, high-quality telemetry alternative to traditional mud pulse telemetry.

The ever-increasing demand for energy resources has led to drilling more complex and challenging wells. The information required to navigate through these complex geologies is provided by highly sophisticated sensors embedded in logging-while-drilling and measurements-while-drilling downhole tools. These combined with rotary steerable systems have made it possible to drill highly deviated, extended reach, and multilateral wells with high precision. Drilling operations can be considered high-risk operations due to the large number of sources that can lead to undesirable outcomes. Therefore, data transmission from downhole sensors and communication with downhole tools is vital to drill safely and successfully a well. Mud-pulse telemetry is the most used telemetry method to transmit the data from downhole tools to the surface. However, advancements in sensor technology and the development of new tools have resulted in higher amounts of data needed to be transmitted to the surface to take advantage of the resolution they now provide fully. The reliance on mud-pulse telemetry, which offers relatively low data transmission speed and broadband, has been the limiting factor, often sacrificing higher drilling rates to obtain the required data quality. The introduction of wired drill pipe, capable of delivering bi-directional telemetry at speeds up to 10.000 times faster than traditional mud-pulse, has removed the reliance on mud-pulse, making it possible to obtain memory-mode quality real-time data. Wired drill pipe also enables the use of along string measurements. These measurement tools are placed along the string and gather pressure, temperature, and drilling dynamics data. Thus, it is now possible to understand the downhole environment along the wellbore and not just a few meters behind the bit. This makes it possible to timely identify well control and well stability events, thereby making risk-informed decisions to mitigate the risk of hazardous events and additionally optimizing drilling operations. The objective of this thesis is to provide a description of the drilling process and the tools that have made it possible to drill the wells that nowadays are drilled. Further, it describes different telemetry methods but focuses on mud-pulse telemetry and its limitations. Then, the wired drill pipe system is extensively described, and it is presented the way it allows the integration of measurement tools along the string. Furthermore, it is shown how these tools enable making risk-informed decisions to reduce the risk during drilling operations. The result is safer drilling operations to be achieved while also saving time by reducing the telemetry time, preventing tool failures, and avoiding resource-demanding well remediation operations. Finally, it is discussed how the availability of real-time high-quality data and full bi-directional instantaneous communication with downhole tools has enabled a step towards more automated drilling operations. The combination of high-speed data transfer with machine learning and artificial intelligence has made it possible to develop autonomous drilling services capable of optimizing the well path and reducing well times

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

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

Online Control and Optimization of Directional Drilling

Directional Steering System (DSS) has been established for well drilling in the oilfield in order to accomplish high reservoir productivity and to improve accessibility of oil reservoirs in complex locations. In this thesis, dynamic modeling of two different DSS were developed and optimized using different control and optimization techniques. Firstly, the Rotary Steerable System (RSS) which is the current state of the art of directional steering systems. In this work, we address the problem of real time control of autonomous RSS with unknown formation friction and rock strength. The work presents an online control scheme for real time optimization of drilling parameters to maximize rate of penetration and minimize the deviation from the planned well bore trajectory, stick-slip oscillations, and bit wear. Nonlinear model for the drilling operation was developed using energy balance equation, where rock specific energy is used to calculate the minimum power required for a given rate of penetration. A proposed mass spring system was used to represent the phenomena of stick-slip oscillation. The bit wear is mathematically represented using Bourgoyne model. Secondly, the autonomous quad-rotor DSS which has 4 downhole motors, is considered. In this work, a novel feedback linearization controller to cancel the nonlinear dynamics of a DSS is proposed. The proposed controller design problem is formulated as an optimization problem for optimal settings of the controller feedback gains. Gravitational Search Algorithm (GSA) is developed to search for optimal settings of the proposed controller. The objective function considered is to minimize the tracking error and drilling efforts. Detailed mathematical formulation and computer simulation were used for evaluation of the performance of the proposed techniques for both systems, based on real well data