Mitigating Stick-Slip Vibrations Using Surface Control Software - A Validation of SoftSpeed II™ Using High-Speed Along-String Dynamics Measurements in a Norwegian Offshore Field

Abstract

Stick-slip is a well known drilling related problem that causes damage and delays, often resulting in an overall more expensive well. These problems have traditionally been remedied by reducingWOB or increasing RPM when possible and most often the ROP is reduced as a consequence. In some cases, it is not possible to compensate for the vibrations as it would stop any progress, and stick-slip must then be tolerated with the potential damages that follows. Remedial processes for stick-slip has been an important field of study. A recent development is the SoftSpeed II™ application by NOV which calculates the downhole bit speed and torque values and implements remedial string rotation to cease several modes of stick-slip vibrations. This way it is not necessary to reduce WOB to cope with the oscillations, and ROP can be maintained. Bit wear will be reduced as a result of mitigating stick-slip, which in a well may mean the difference between continued progress or an expensive bit trip. Other side effects may include reducing lateral and axial vibrations, reducing wear on BHA and drillstring, and improving borehole quality. This Thesis will study the use of SoftSpeed in one field located in theNorwegian North Sea. The reservoir contains hard conglomerates which has created high level of vibrations in previouswells. SoftSpeed has been implemented on the last two reservoir sections, and these two will be compared to the previous four sections drilled in the same reservoir. By using data from along-string dynamic sensors, the effects of SoftSpeed on drillstring vibrations and locally induced stick-slip can be analyzed at different intervals in the well in high resolution. Performance parameters, such as Rate of Penetration (ROP) andMechanical Specific Energy (MSE) alongside with a derived Stick-Slip Severity index (SSS), will ensure equal comparison between the wells.