Basic Surveyers Course

Basic Surveyors Course2005 Mike Meadows ConsultancyRevisions2007 APS Technology, Inc.

1ContentsIntroductionSurvey ReferencesSurveying ToolsMore Surveying TermsQuality ControlsSurveying CalculationsTRCIntroductionSection 1 A Surveyors JobThere are worse jobs!

Why Survey a well?To hit geologic targetsTo avoid collision with other wells, especially during platform drillingTo define the target of a relief well in the event of a blowoutTo provide a better definition of geological and reservoir data to allow for production optimizationTo fulfill the requirements of local legislation, e.g. Texas Railroad CommissionWhat do surveys do?Measure the inclination and direction at the bottom of the hole to determine where the well is headingDetermine orientation of tool face of deflection tools or steerable systemsCalculate well coordinates at a series of measured depths to accurately specify the well path and current locationIdentify dog legs and allow calculation of dogleg severity valuesWhat is actually measured?InclinationDirection (Azimuth)DepthInclinationA number from 0 to 180000 is straight down900 is horizontal"The inclination of a borehole at a point is the angle between the borehole axis and the vertical"

200DirectionWhich way is the well pointed?Direction is the angle between a reference direction and a tangent to the horizontal projection of the well at the point of interest"

NSWEDirectionQuadrantNumber from 0 to 90 measured east or west of north or southe.g., S40W Older system

AzimuthMost commonNumber from 0 to 360 degrees, measured clockwise from Northe.g., 220 NWES30609060309030606030NWES306090120150270330300240210180Map ProjectionsA good approximation of the shape of the earth is that of a spheroid (flattened sphere)The location of a point on a spheroid can be described by two angles.Latitude is the angle between a line joining the point to the center of the spheroid and the equatorial plane.Longitude is the angle between a plane containing the point and the axis of rotation and another plane containing an arbitrary reference point and the axis of rotation.

Polar flattening

LongitudeLines of Longitude are lines drawn through the north and south poles, and are called meridians.They measure distance east and west of the prime meridian which was established near Greenwich, England.The prime meridian is the 00 line. Longitude measures 00 to 1800 east and 00 to 1800 westEastern and western hemispheres meet at1800 the International Date Line

LatitudeLines of latitude are drawn around the earth parallel to the Equator. They are called parallels.They are equally spaced in degrees not miles.The equator is 00 and the poles are 900.

PositionLatitude lines are typically shown for every 10 degrees, starting at the equator; the longitude lines are shown for every 15 degrees, starting at the prime meridian.What is the position at the green dot?

Answer:20N45EMap ProjectionsA map projection is used to portray all or part of the round Earth on a flat surface. This cannot be done without some distortion.Every projection has its own set of advantages and disadvantages. There is no "best" projection.The mapmaker must select the one best suited to the needs, reducing distortion of the most important features.

Map ProjectionsDifferent kinds Mercator, Conic, Polyconic, Lambert's ConformalMercator based on a cylinder, only true at equator, useful for navigatorsLambert's maps used by military and basis of US Aeronautical charts.Conic ProjectionLambert Conformal Conic map is made by projecting the globe onto a cone."Conformal" means that this map represents the shape of limited areas accuratelyUsed to show parts of globe that run east west at middle latitudes e.g. United States

Mercator ProjectionMercator map is very commonFor areas close to equator, map accurately represents the shape.Badly distorts landmass at the poles Alaska looks size of South America actually South America is 11 times bigger than Alaska

Transverse Mercator ProjectionSimilar to Mercator but orientation of cylinder is differentUsed by USGS for quadrangle mapsUniversal Transverse Mercator UTM is a series of 60 Mercator projections each covering 60 of longitude.

Survey ReferencesSection 2 Borehole Survey ReferencesAll measurements must be tied to fixed reference systemsDepth ReferencesInclination ReferencesAzimuth ReferencesDepth ReferencesMeasured DepthDistance measured along actual course of borehole from surface to survey point. Pipe tally or wireline depth counter.True Vertical Depth TVDVertical distance from depth reference level to a point on the borehole course. Usually a calculated value.

RKBWhile drilling it is convenient to use the top of the rotary table as the working depth reference. This is called Rotary Kelly Bushing (RKB)Offshore, mean sea level (MSL) is sometimes usedOn floating rigs, a mean RKB is used

RKBInclination ReferenceInclination is the angle between vertical and the tangent to the well bore axis at a particular pointConvention is 00 is vertical 900 is horizontalInclination may be >90 for some horizontal wellsSometimes called Drift

Azimuth ReferencesThree systemsMagnetic NorthTrue (Geographic) NorthGrid NorthAll magnetic type tools initially measure azimuth referenced to Magnetic NorthMagnetic North is constantly changing, so final calculated coordinates are always referenced to either True North or Grid North to obtain a stable reference.True NorthTrue North: Is a line from any point of the earth's surface to the geographic north pole. All lines of longitude are true north. True north is depicted in the declination diagram by a line with a star. The top of USGS topographic map sheets are oriented to true north.

Grid NorthGrid North: The north directional on a mapGrid North is identical to True North only at specified meridians.All other points must be corrected for convergence (the angle between Grid North and True North at any given location).GGGNGGG0aCentral MeridianTrue NorthMagnetic DeclinationMagnetic Declination is the angle between true north and magnetic north at any point on the earthMagnetic north moves every day.

Magnetic DeclinationDeclination changes with location on earth and timeTo determine declination, you need to know if magnetic north is east or west of true north from the locationStated as an angle and whether E or W

Agonic LineEast DeclinationWestDeclinationMagnetic DeclinationAlso referred to as variation, magnetic variation and compass variationMathematical models exist to calculate declination at any point on earth at any date International Geomagnetic Reference Field (IGRF) are produced every 5 years. 2005 is the latest.

East DeclinationEast declinations occur when magnetic north lies east of true north with respect to the location.True for any location west of the zero declination (Agonic) line e.g. west Texas, CaliforniaValue is added to magnetic readingExample - Declination of a location in Bakersfield, CA is 130 38' E, magnetic survey reading is 1380 04' azimuth azimuth with reference to true north is 1510 42'West DeclinationWest declinations occur when magnetic north lies west of true north with respect to the location.True for any location east of the zero declination (Agonic) line e.g. Florida, GeorgiaValue is subtracted from magnetic readingExample - Declination of a location in Mobile Bay, AL is 00 45' W, magnetic survey reading is 2450 04' azimuth azimuth with reference to true north is 2440 19'http://www.ngdc.noaa.gov/seg/geomag/declination.shtmlDeclination Memory AidCADETCompass to True Add East

CADETGrid ConvergenceWhen maps are created, coordinates must be transferred from a sphere to a flat surfaceDepending upon the projection used, there will be a distortion between true north and map or Grid NorthConvergence is the angle between grid north and true north for the location being considered.GGGNGGG0aCentral MeridianTrue NorthToolfaceUsed with deflection tools or steerable motorsCan be physically marked on a tool scribe line"Toolface Orientation" is the angular measurement of a deflection tool with respect to either up (highside) or to NorthHighside ToolfaceAlso referred to as Gravity ToolfaceIndicates whether the toolface of a deflection tool is facing up 00 or down 1800 or any angle from left or right of highside.Used once a wellbore has an angle of greater than 30 to 50 of inclinationTool FaceUp(High side)Scribe LineMagnetic ToolfaceOnly used at very low inclination angles typically