Overview:
• There is a vital need for representative and justifiable error model for safe and reliable surveying when using gyroscopic tools
• The paper illustrates the procedures adopted by one gyro service company for the extraction of realistic error model data - new set of uncertainty estimates for some
existing gyroscopic tools
• Individual service companies can and should provide error models based on real downhole data for each type of tool and service on offer
• Substantial effort and resource commitment are needed to generate error models
MWD Survery Error Models
• SPE 67616 by Williamson outlines the mathematical framework and numerical inputs for MWD surveys error model
– MWD sensor performance is somewhat similar
– Magnetic field distortions and fluctuations are the main source of errors
• SPE 90408 by Torkildsen outlines only the mathematical framework gyro survey tools
– Gyro sensor performance greatly varies between companies
– Earth Rotation rate is a very stable reference, main source of error is related to the sensor performance
Objectives
• To start a process to close a potential safety gap associated with “unproven gyroscopic error models”
• To present the derivation of a set of realistic uncertainty estimates for gyroscopic tools based on statistical analyses of real downhole data
• To emphasize the fundamental issue of linking error
models with QC procedures
....
View the entire Presentation:
Improving the Quality of Ellipse of Uncertainty Calculations
Roger Ekseth et. al. - Gyrodata