4.2.5 Tool Error Model and Term Set Data Objects

Tool error models are used to specify the inaccuracies of instruments or measurement systems. The instrument inaccuracies are often referred to as “modellable errors” whereas the practical or usage mistakes are referred to as “unmodellable errors”. These error models define how various error sources affect the observations in the well and thus the positional uncertainty along the wellbore. Industry-standard error models are used to ensure that best practice has been adopted before assuming that the calculated uncertainties are representative. A tool error model term set provides the error terms that are used in the tool error model.

Work in the industry related to error models and the design of these data objects is based on work by the Industry Steering Committee on Wellbore Survey Accuracy (ISCWSA), which is affiliated with the Society of Petroleum Engineers Wellbore Positioning Technical Section (SPE-WPTS).