Guidelines for GNSS Positioning in the Oil and Gas Industry

Transcription

1 Guidelines for GNSS Positioning in the Oil and Gas Industry The Hydrographic Society in Scotland Aberdeen Wednesday 20th April Gordon Johnston

2 Introduction The motivation to introduce a set of Guidelines The main stakeholders, IMCA and OGP The formation of and the activities of the joint Working Group The New Guidelines and some of the significant elements Conclusions and recommendations

3 Background and Motivation During the decade it became apparent that there was no single source suitable for DGPS good practice in the offshore Oil and Gas industry. Two organisations, IMCA and OGP independently concluded that the pre existing 1994 GPS Guidelines were out of date and considered that the industry would benefit from an up to date document. So, late in 2008 they agreed to form a Joint Working Group to review the situation and recommend a way forward. The plan, to update, revise and generate a new set of Guidelines was approved in early But who are IMCA and OGP?

4 IMCA is. The International Marine Contractors Association: An international trade association for offshore, marine and underwater engineering companies established to represent the collective interests of its members, interface with oil & gas operators, governments and regulatory bodies. The secretariat is based in London (Victoria) with 21 full time staff members from 58+ countries IMCA was formed 1995 through the amalgamation of AODC (founded in 1972 and originally the International Association of Offshore Diving Contractors) and DPVOA (founded in 1990 as the Dynamic Positioning Vessel Owners Association). Visit IMCA at

5 IMCA structure

6 Offshore Survey Division Technical documents that may be familiar to you Guidelines for the use of multibeam echosounders for offshore surveys Digital video offshore: A review of current and future technologies Rev. 1 The shared use of DGPS for DP & survey operations The shared use of sensors for DP & survey operations Rev 1 Guidelines on installation and maintenance of DGNSSbased positioning systems Deep water acoustic positioning Discovering digital video: An introduction to digital video and its benefits

7 Offshore Survey Division Work programme forthcoming documents IMCA/OGP review of the UKOOA DGPS Guidelines Guidance on specification of GNSS systems for DP vessels Technical review of subsea metrology Guidance on USBL installation on new-build or chartered vessels Guidance on data management and security An offshore survey mobilisation checklist Proposed guidance on GIS Proposed guidance on inertial navigation systems

8 And OGP is. The International Association of Oil & Gas Producers Over 70 members around the world OGP s membership includes upstream companies, national and international associations and major contractors. OGP s member companies produce over half of the world s oil and over a third of its gas. OGP serves its members from it HQ in London and an office in Brussels dedicated to EU issues.

9 OGP Committees OGP is a committee-based organisation, with members providing the participants of 11 standing committees. These committees, each of which reports to the Management Committee, focus on: Decommissioning European Union Health Metocean Safety Standards Environment Geomatics Legal Offshore Structures Security Each committee has its own specialist subcommittees and task forces

10 Geomatics Workplan Guidelines for GNSS Positioning in the Oil and Gas Industry Conduct of Drilling Hazard Site Surveys AND Technical Notes Seabed Survey Data Model P-formats GIGS Guidance Involvement in ISO TC211 (GI & Geomatics) CRS Registry & Polygon through the EPSG Geodetic Parameter set For more information about OGP, visit:

11 The Revision A Work Group was formed, initially with 3 IMCA & 3 OGP members however it was recognised that this would be too restrictive. The Work Group was expanded to include stakeholders, making it 11 persons. The plan, to update, revise and generate a new set of Guidelines was approved in early 2009 and work commenced. Since then the Work Group has met 9 times at various locations, as well as holding over 10 formal teleconferences. As well as the main revision tasks, input from the Work Group and the IMCA and OGP survey committees produced over 250 items in 2009 and in 2010 another 300+ points for edit were resolved.

12 The expanded Work Group The expanded Work Group comprised IMCA, OGP and Stakeholder representatives. Gordon Johnston (c) Venture Geomatics (United Kingdom) Craig Allinson BP UK (United Kingdom) Ed Danson C&C Technology (US and United Kingdom) Palle Juul Jensen Maersk Oil & Gas (Denmark) Kees de Jong Fugro Survey (Netherlands) David Mann Gardline Survey (United Kingdom) Sverre Olsen PGS (Norway) David Russell Veripos (US and United Kingdom) David Claude Simon Total (France) Frederic Terrand CGGV (France) Kenneth Welker WesternGeco (Norway) Nick Hough IMCA (Secretariat) (United Kingdom)

13 The challenge is to provide relevant and valuable information on the performance of positioning. The existing UKOOA document was a hard act to follow. This must apply to both the standard solutions (blue) using pseudo range observations as well as the newer phase based solutions (red). The Objective

14 The Work Group s Material The main document sections are now as follows: Executive Summary Glossary Introduction and Background Installation and Operation Quality Measures Competencies Receiver Outputs & Data Exchange Formats

15 The New Guidelines - Content The document has new major updated sections: Introduction and Background Up to date observables, latest generation relative & absolute techniques, service providers and types of systems available. Installation and Operation The influences of work areas, installations, Geodesy and verifications & checks. An important practical rather than academic section. Quality Measures Revised section with updated examples and an emphasis on operational examples. This is retained as a key section.

16 00:00 00:15 00:30 00:45 01:00 01:15 01:30 01:45 02:00 02:15 02:30 02:45 03:00 03:15 03:30 03:45 04:00 Error (m) New Techniques pose new Challenges Error sources that were not in the UKOOA 1994 Guidelines includes orbit and satellite clock errors that are key components of the latest positioning techniques. However these are actually not really dealt with as they do not have characteristics that can be easily identified by statistical testing. These are systematic errors Age of orbit and clock parameters (hh:mm) 3D orbit error Clock correction error

17 Precision measures Reliability measures Accuracy Statistical testing Quality Measures Quality Measures

18 Quality Measures Precision measures: a very precise fix is one in which the random errors are small and repeatability therefore is high. Such a fix is said to be of high precision. The Standard Deviation, or the Variance or Standard Error are the common terms.

19 Measures of Performance

20 Quality Measures Reliability Measures: Reliability is most usefully measured by means of Marginally Detectable Errors (MDE). In order to understand MDEs it is necessary to understand the basis of statistical testing. It should be emphasized that the DGNSS Guideline is concerned with outliers and consequently reliability is interpreted as the ability of a system to detect outliers and its sensitivity to undetected outliers. Internal reliability: observational MDEs External reliability: positional MDEs These are generally listed as tabular values

21 Quality Measures Accuracy: This can be considered as a combination of the two elements Precision and Reliability. A high accuracy means high precision, high repeatability, the ability to detect small outliers in observations and a small impact of undetected outliers on the parameters of interest, i.e. the estimated positions. Statistical testing: The method used is an implementation of the Receiver Autonomous Integrity Monitoring (RAIM). Quality Measures: The 2D error ellipse or 3D error ellipsoid as a precision measure. The largest horizontal position vector resulting from a Marginally Detectable Error as a measure of external reliability.

22 The Recommended Test Statistics The w-test and the F-test (unit variance test): w-test: used to detect outliers. Observation residuals for which the magnitude of the w-test statistic, is greater than are highlighted for each position fix. If more than one outlying observation is highlighted in a fix, then only the largest is rejected and the computations repeated. Acceptance criteria requires that the mean w-test should have an average value equivalent to zero over a period of time (e.g., one line). F-test: used to verify the model which is being used to account for errors in the GNSS observations (e.g., atmospheric refraction, multipath, differential corrections). This is done by verifying that the average value of the unit variance is 1. It s not true that a value not equal to one is a bad fix. Acceptance criteria would require that the mean of the unit variance computed by the F-test for a period of time (e.g., one seismic line) should be statistically equivalent to one. These test statistics should be used continuously.

23 Statistical testing

24 The Quality Measures computed and examined for each fix are: The error ellipse and external reliability (3D positional Marginally Detectable Error). Error ellipse: an approximate graphical representation of the positional precision in two dimensions. It should be used to indicate the size of random errors in the position and also the direction in which the errors are occurring, External reliability: the largest effect on the estimated position of an observational MDE. The positional MDEs for each observation are a means of describing how reliable it is (i.e., how well it can be checked by other observations). MDEs should be computed for each observation (pseudo-range or carrier phase) included in the computation. Significance level of 1% Detection power of 80% This means there is a 20% chance that a gross error less than or equal to the stated value of the observational MDE will remain undetected.

25 New & Updated Content The New Guidelines include sections that cover: New techniques and the main source of service providers this includes an overview of the GNSS methods of positioning for the horizontal and for the vertical. Installation and Operation now incorporates sections on the preparation, installation and commissioning of systems as well as in-field verification. Regional influences and the impact of an active solar cycle An overview of Risk Management and potential mitigation considerations for different installations are also covered. Not forgetting an introduction to Quality Measures & Statistical testing.

26 Summary and Conclusions Guidelines for GNSS Positioning in the Oil and Gas Industry. The document is a vast improvement on the previous Guidelines. It represents a clear and up to date view on: what we can consider good practice and offers recommendations on the quality parameters to use It has new sections with elements relating to atmosphere, areas of operations & the verification of installations. The main Appendix retains the mathematical outlines of the computations and importantly includes numerous worked examples to support the Guidelines. It is recommended you update your documentation to include the new IMCA-OGP DGNSS Guidelines.

27 Questions? Contact details: IMCA: OGP: Gordon Johnston: Nick Hough: Abby Findlay: