| dc.description.abstract | 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 drilling
vibration. The Case study has following objectives:
Understanding drilling dynamics in real time.
Analysing the undetected damages and work towards improved detection methods
with 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 the
eccentric 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 the
report spots shortcomings in existing detection methods. The report has following
main observations:
1. The existing vibration detection criteria avoids the damage on the Bottom hole
assembly (BHA) only. The ASMs lie in the drillpipes which are more flexible
and weaker than the BHA. Hence, there is a need of multiple criteria to avoid
damages 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 detection
criteria are independent of the effect of depths and inclination on the drillstring
dynamics.
3. Existing criteria are unable to flag the forward synchronous mode as the FSW
vibration levels lie in the tolerant zone.
4. The synchronous whirl needs continuous presence of parameters to develop. Thus
the 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 focused
on 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 induce
other modes of vibration.
The project is limited to acknowledge the presence of drilling dynamics. Due to
the lack of evaluating parameters, there are no comments made on severity of the
vibration. For future work, the report suggests to develop a dynamic detection system
which shows the probability of every mode of the drilling vibration by considering the location of the tool in the well. | en |
