OWSG Standard Survey Tool Error Model Set for Improved Quality and Implementation in Directional Survey Management
Authors: Grindrod S. J. , Clark P. J. , Lightfoot J. D. , Bergstrom N. , Grant L. S. 
Published: January 2016

Abstract
Understanding wellbore position and the associated uncertainty is fundamental to all drilling operations and reservoir management. Without consistency in predicting to known uncertainties, activities involving positional uncertainty, such as risk mitigations for collision avoidance, cannot be performed reliably with known confidence. For the first time, industry has a common controlled set of uncertainty models thus allowing for transparency in error estimation. Reservoir targeting and subsurface hazard avoidance can be compromised resulting in unrealized stranded reserves and/or intersection of faulted, undesirable formation. Overly optimistic estimations can result in wellbore collisions where the risk of collision is assumed to be very low or can result in a missed well intersection during relief well first ranging point operation. Conversely, overly conservative estimations can result in excessive targeting constraints or directional control requirements.
An analysis of industry survey of error codes being utilized across companies was performed, both vast inconsistencies and significant gaps were realized. A case for action was determined and a collaborative work group was formed under the Operator Wellbore Survey Group (OWSG). OWSG is a subcommittee of the SPE Wellbore Positioning Technical Section (SPE-WPTS). The SPE-WPTS originated as the Industry Steering Committee on Wellbore Surveying Accuracy (ISCWSA), which affiliated to the SPE and became a Technical Section.
It was determined that many of the error codes being utilized in industry were based on survey tool error models established in SPE 67616 and SPE 90408, but there were uncontrolled changes, miss matched versions, and alterations in error assumptions (that were not vetted) being unknowingly utilized. Inspection revealed that the error models, although loosely based on ISCWSA, were varied across both service and operator companies and in some cases were varied internal to individual companies.
The collaborative work group was established to develop a Standard Survey Tool Error Model Set based on the SPE 67616 and SPE 90408 publications, the current work of the ISCWSA error model subcommittee and with contributions from industry's leading subject matter experts. The result of the work is a series of 5 sets of OWSG Survey Tool Error Models. The sets have a Model Selection guide with a Standardized naming structure.
The Standard Survey Tool Error Model Set has been released into the public domain to improve Survey Management Quality and has been adopted by numerous companies (both services and operators). The OWSG error model set facilitates easy implementation in all common directional well planning software platforms; hence reducing risk of incorrect models leading to poor understanding of wellbore position and improving consistency of error estimation.
The Standard Survey Model set has been compiled with contributions from industry's leading subject matter experts. The most recent second revision (Rev2) of sets A and B of the series were publicly released during the month of June of 2015.