Well Geodetics and the importance of Geodesy in Master Data Management
Well Geodetics and the importance of Geodesy in Master Data Management
NeuralogWell Geodetics in Master Data ManagementRobert E. BestDean C. Mikkelsen Turning Paper Into Petroleum
Outline What is Well Geodetics? Why is it Important in MDM? Geodesy Concepts Standards Implementation in MDM Summary
What is Well Geodetics? The science of locating a well’s surface and bottom locations. Location with respect to other features: Other wells Geopolitical boundaries Hydrocarbon targets Geological features
Why is it Important? When combining well data of different ‘vintages’, different systems may have been used. In order to accurately map your wells, geologic features and boundaries together, the same Coordinate Reference System (CRS) must be used.
Dramatic example of what might happen Lake Peigneur, Louisiana, USA 1980. Well drilled a little too close to salt dome.
Result Lake drained in 2 days. Rig and several barges lost (no life lost) Freshwater lake became a saltwater lake
Bottom Line : Check the CRS Failing to account for these differences can create errors of 100’s of meters. A wells report from the 1951 may have a completely different CRS than one from 2001. The main factors are the CRS used Datum - Ellipsoid Projection - North Reference
Reference Systems and Coordinates Depth Reference Measured Depth True Vertical Depth Inclination Reference Vertical Reference Direction Measurement Azimuth Reference Quadrant Bearings
Depth Reference Points – Land and Offshore Rigs Elevation: Kelly Bushing, Ground Level, Elevation above Mean Sea Level (MSL), MSL Land Rig Offshore Rig Elevation: Platform, Seabed, MSL, Kelly Bushing Vertical Component of well location is vital to integrity of the data set. Correctly referenced height data (ellipsoid, elevation or z). May prove challenging for legacy data.
Map Projections Map projections display the earth on a ‘developable’ surface Plane Cone Cylinder Distortion will be a result Shape Azimuth Linear
Universal Transverse Mercator Widely used internationally Zone/Grid system 60 Zones, 6deg width
UTM Grid Positive Easting and Northing coordinates Grid Convergence (difference between true/grid north) zero at equator and central meridian
North Reference Azimuth measurements, such as in a well deviation survey, require a North Reference. ‘North’ can be referenced to one of the following: True North Direction of the Earth’s Northern Geographic Pole Grid North Map North (North Direction of the Y-Axis of a Cartesian Grid) Magnetic North Direction of the Earth’s Northern Magnetic Pole
Grid North Reference North direction parallel to Y Axis of map
Grid North Reference - UTM True North Grid North Angle between the two is the Grid Convergence Angle
Application in Well Deviation Surveys 3 basic measurements Azimuth (with respect to a North Reference) Deviation Angle (from vertical) Measured Depth Standards vary for North Reference but some basic rules of thumb: International/Onshore USA – True North Offshore USA – Grid North
Application in Well Deviation Surveys Q: What happens if the wrong North Reference is used? A: The well bottom hole location will be in the wrong place! In UTM, the issue is more acute the farther you get from the equator and central meridian.
Datums and Ellipsoids The earth is usually modeled as a ellipsoid. Regional maps frequently employ a datum to better match the area by employing an ellipsoid shift
Common Ellipsoid & Datums European Datum International North American Datum Clarke 1866 WGS Datum Tokyo Datum Bessel South American Datum International Arc Datum Clarke 1880
Horizontal Datums Many nations established their own datum Standards and procedures vary widely Coordinates from different datums are completely incompatible Relative to Initial Point of Datum Will vary as a function of Ellipsoid parameters
Datum Transformation – 7 Parameter – One Method
To translate one datum to another we must know the relationship between the chosen ellipsoids in terms of position and orientation. The relationship is defined by 7 constants.
3 - Distance of the ellipsoid center from the center of the earth (X, Y, Z)
3 - Rotations around the X, Y, and Z of the Cartesian Coordinate System Axes (, , )
Scale change (S) of the survey control network
Transformation between 2 Horizontal Datums The two ellipsoid centers called X, Y, Z The rotation about the X,Y, and Z axes in seconds of arc The difference in size between the two ellipsoids Scale Change of the Survey Control Network S
What does this mean? Longitude and Latitude are not unique for a given location. Must know the associated datum f1 f2 f1 ¹f2
Units of Measurement Several different units of measurement have been used in location of wells and seismic. Unambiguous identity and correct knowledge and application of units of measurement are required. Eg. “Foot” might be any of the following: International Foot US Survey Foot British Foot (Sears 1922) British Foot (Benoit 1895 A & B, 1865, 1936) Indian Foot (1937, 1962, 1975) Gold Coast Foot
Standards – OGP/EPSG/UKOOA The OGP Geomatics Committee is now the custodian of upstream geodesy information for international E&P Was born from the European Petroleum Survey Group (EPSG) and UKOOA Standards. http://info.ogp.org.uk/geodesy/
EPSG Database Comprehensive database of ellipsoids, datums, projections and coordinate reference systems used worldwide
Standards - APSG Formed in 1998 to promote exchange of ideas and issues encountered in worldwide E&P. Individuals come from within the oil and gas industry, from majors to service companies. Definitions of multiple Horizontal Datums http://www.apsg.info/
Implementing Geodetics in MDM Given the previous discussion, a Master Data Management Solution should be able to: Support grid and Lat/Lon coordinates Support individual CRS for an entity (well, seismic navigation, etc) Support the storage of the geodetic metadata to specify the CRS
Example MDM Model - PPDM Professional Petroleum Data Management Association International Data Modeling consortium Members companies include Oil & Gas and Technology Firms Model refined over 20 years http://www.ppdm.org/
CRS Tables in PPDM CS_COORDINATE_SYSTEM CS_PRIME_MERIDIAN CS_GEODETIC_DATUM CS_ELLIPSOID
Transformations in PPDM CS_COORD_TRANSFORM CS_COORD_TRANS_PARM CS_COORD_TRANS_VALUE
Well CRS in PPDM WELL WELL_NODE CS_COORDINATE_SYSTEM
Well Deviation Survey in PPDM WELL CS_COORDINATE_SYSTEM WELL_DIR_SRVY WELL_DIR_SRVY_STATION
PPDM Implementation Each entity (well, seismic, etc) has individual CRS specification for pertinent locations. Datum, Ellipsoid and Transformation parameters stored and tied to CRS. Full parameters needed for transformation to any system stored.
Conclusions and Recommendations Gather and store all the geodetic meta-data available for your wells and seismic. Be aware of how missing or incorrect information can effect your mapping. Employ a MDM strategy to account for these factors at the outset.
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