An Analysis on Drillstring Vibration - A novel approach to detecting Forward Synchronous Whirl
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Operators acknowledge the value of investment in controlling drilling dynamics. Decrease in crude oil prices limits the investment on measurement tool competences.Thus, it is necessary to address the drilling dynamics with limited tool competences.The vibration detection methods in real time are prioritized, as in a low profit margin environment, any savings in damage-related expenses can yield a significant return on the investment. National Oilwell Varco has advanced wired drillpipe technology which significantly increases data gathering capabilities, as well as Along-String Measurement (ASM) tool which shows the dynamics along the length of the drillstring. However, the existing detection system is unable to detect low-energy dynamic events which has the potential for causing damage, such as eccentric wear. This thesis is based on events that took place in the North Sea while drilling a number of production wells. A well was drilled successfully, seemingly without any drilling dynamics-related concerns. After having pulled the drill string out of the hole, however, eccentric damage to drill string components were observed. The intention of this thesis is to analyse the drilling dynamics events that may have caused this damage, and to compare the dynamic environment of thewell in question with comparablewells. This thesis is an analysis on drillstring vibration. The report has two main parts:Theory and Case studies. The theory gains the existing understanding of the drillingvibration. The Case study has following objectives: Understanding drilling dynamics in real time. Analysing the undetected damages and work towards improved detection methodswith ASMs. The analysis shows the need to pursue multiple and progressive detection criteria.The methodology focuses on improvising the analysis in real time. To address theeccentric damages, the forward synchronous whirl (FSW) is studied. The characteristics properties of the synchronous whirl are developed as multiple indicators. These indicators are tested in the real time data of well X and Y which showed post well indications of the FSW mode. Furthermore, the indicators are used in the analysis of the well Z. There were no visual damages reported in the well Z. In addition to the FSW mode, the vibration detection methods are studied and thereport spots shortcomings in existing detection methods. The report has followingmain observations: 1. The existing vibration detection criteria avoids the damage on the Bottom holeassembly (BHA) only. The ASMs lie in the drillpipes which are more flexibleand weaker than the BHA. Hence, there is a need of multiple criteria to avoiddamages on both BHA and the ASM 2. ASMs are located at different depths of the well. Thus with changing depths, tension or compression, side forces and stiffness in the drillstring changes. The report spots the need of progressive criteria for ASM tolerances. Current detectioncriteria are independent of the effect of depths and inclination on the drillstringdynamics. 3. Existing criteria are unable to flag the forward synchronous mode as the FSWvibration levels lie in the tolerant zone. 4. The synchronous whirl needs continuous presence of parameters to develop. Thusthe depths with consistently higher side forces and low rate of penetration (ROP)areas can induce such modes of vibration. At present, the analysis is only focusedon the low ROP regions. 5. Build up section shows high lateral activity. 6. Synchronous mode occurs in synergy with the rotation of the drillstring. Thus,it is a low energy mode. Such dynamics do not contain enough energy to induceother modes of vibration. The project is limited to acknowledge the presence of drilling dynamics. Due tothe lack of evaluating parameters, there are no comments made on severity of thevibration. For future work, the report suggests to develop a dynamic detection systemwhich shows the probability of every mode of the drilling vibration by considering the location of the tool in the well.