2.positioning

Instituto Superior TécnicoUniversidade de Lisboa

Masters in Petroleum Engineering 2014-2015

Drilling Engineering Course

José Pedro Santos Baptista

Mining and Geological Engineering Msc.Petroleum Engineering Msc.

Drilling Engineering Course

2

2. Positioning

Geodesy

Concept overview – What’s the Workflow?

Referencing

Local Coordinates and Depth References – Why?

Well Head Placement

Where to Drill – What are the key drivers?

Drilling Engineering Course 2014-2015 Masters in Petroleum Engineering

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Geodesy – Definitions


Greek

Division of the Earth (geodaisia) – Primarily concerned with positioning within the temporallyvarying gravity field.

German

Higher Geodesy ("Erdmessung" or "höhere Geodäsie") – measuring the Earth on the global scale.

Practical Geodesy or Engineering Geodesy ("Ingenieurgeodäsie") – measuring specific parts orregions of the Earth (incl. surveying).

Study of the shape, size and geometrical surface of the Earth (incl. Datum)

Reference Ellipsoid

Mathematically defined surface that approximates the true figure of the Earth (Geoid).

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Used as a preferred surface on which geodeticnetwork computations are performed and pointcoordinates are defined (e.g. latitude, longitude, andelevation).

Reference Ellipsoid

Its shape is determined by an imaginary ellipse which generates the ellipsoid when it is rotated aboutits minor axis.Each nation might use its own model in order to obtain a better fit of its own territory.

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Reference Ellipsoid

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Semi-major axis 𝑎

Inverse Flattening 1

𝑓

Semi-minor axis 𝑏 = 𝑎(1 − 𝑓)

Ellipsoid Parameters

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Datum

Reference point or surface against which position measurements are made, and an associated model ofthe shape of the earth for computing positions.

Horizontal datum Used for describing a point on the earth's surface, in latitude andlongitude or another coordinate system.

Vertical datum Used to measure elevations or underwater depths.

Built on top of a selected ellipsoid incorporating local variations of Lat,Long and elevation to reflect thespecificities of a particular region.

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Datum

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Latitude, φ

Geographic coordinate that specifies the north-south position of a point on the Earth's surface.Angle which ranges from 0° at the Equator to 90° (North or South) at the poles.Lines of constant latitude (parallels) run east-west as circles parallel to the equator.

Longitude, λ

Geographic coordinate that specifies the east-west position of a point on the Earth's surface.Angle which ranges from 0° at the Royal Observatory, Greenwich, England (Prime Meridian) to180° East or West.Points with the same longitude lie in lines running from the North Pole to the South Pole.

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Map Projections

Systematic transformation of the latitudes and longitudes oflocations on the surface of a sphere or an ellipsoid into locationson a plane.

All projections distort the surface in some fashion.

Depending on the purpose of the map, some distortions areacceptable and others are not.

When converting a projection back to an ellipsoid a correctionfactor must be considered (convergence angle).

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Map Projections

There are several different types of projections in order to preserve some properties of the sphere-like bodyat the expense of other properties. There is no limit to the number of possible map projections (cylinder,cone and Azimuthal or plane).

Cylinder Cone Plane

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Map Projections

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Map Projections

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Geographic Coordinate System

A geographic coordinate system enables every location on the Earth to be defined by a set of numbers orletters.

Coordinates are often chosen such that one of the numbers represents vertical position, and two or threeof the numbers represent horizontal position.

A common choice of coordinates is latitude, longitude and elevation.

Latitude and longitude values can be based on different geodetic systems or datum, the most commonbeing WGS 84, a global datum used by all GPS equipment.

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15Drilling Engineering Course 2014-2015 Masters in Petroleum Engineering

UTM CoordinatesGPS UTM

Developed by the US Army Corps of Engineers in the 40s in

order to design grid maps for military purposes.

Divides the Earth into 60 zones (not a single map projection)

6 degree band of longitude

Secant transverse Mercator projection

Between 80°S and 84°N latitude


2. Positioning


UTM Coordinates

The true origin of the UTM coordinate System is the interception ofthe central meridian with the equator.

The limits of the UTM zone are the same (to all zones) 6° meridian(longitude)

Northings and Eastings are always positive

UTM zones get thinner when approaching the poles


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UTM CoordinatesNATO/Military UTMThe military grid reference system

Each zone is segmented into 20 latitude

bands. Each latitude band is 8 degrees

high, and is lettered starting from "C" at

80°S, increasing up the English alphabet

until "X", omitting the letters "I" and "O"

(due to their similarity to the numerals one

and zero).


Ellipsoid

• Airy (1830)

• Everest (1830)

• Clarke (1880)

• Krassovsky (1940)

• WGS-84 (1984)

• Etc..

Datum

• NAD 27

• NAD83

• ED50

• WGS84

• Etc…

Projection

• Preserving direction: Azimuthal

• Preserving shape: conformal

• Preserving area: equiareal

• Preserving distance: equidistant

• Preserving shortest route: gnomonic

• Etc…

Coordinate System

• Geographic

• UTM

• Stereographic

• Cartesian

• Etc…

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Geodesy – Workflow


Workflow

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Referencing


Local Coordinates

Selecting a location: Ellipsoid, Datum, Projection and the Coordinate System

Selecting a reference point (known coordinates) as an origin, from where all the measurements can becarried out

These measurements are referred to as Local Coordinates

X,Y,Z

These coordinates are often used due to the simplicity in, not only collecting data, but also for ease inobtaining distances and reaching the desired location within a area (i.e. oilfield)

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Referencing


North – Surveying

When a measurement (survey) is taken the tools used (GPS, Total Station theodolite, MWD, Gyro, etc..)may yield different values for the same point (even with the same geodetic system)

N (0°)

S (180°)

E (90°)O (270°)

+

I

Azimuth Inclination

True North

Magnetic NorthTrue North

Grid NorthN

S

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Referencing


North – Surveying

The azimuthal references areparticularly affected

True North

Grid North

Magnetic North

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Referencing


North – Surveying

True north (geodetic north)

Direction along the earth's surface towards the geographic North PoleWhere the imaginary Rotational Axis of the Earth intersects the surface

Grid north

Navigational term referring to the direction northwards along the gridlines of a map projectionEqual to the true north in the central meridian (parallel to the YY axis ofthe map)

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Referencing


North – Surveying

Grid convergence

Horizontal angle measured from true north to grid north.

True north and grid north are the same along the centralmeridian of the UTM grid zone.

Outside of the central meridian, true north departs fromgrid north due to the convergence of the meridians.

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Referencing


North – Surveying

Magnetic north

Point on the surface of Earth's NorthernHemisphere at which the planet's magneticfield points vertically downwards(perpendicular)

The North Magnetic Pole moves over timedue to magnetic changes in the Earth'score (55 and 60 km per year).

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Referencing


North – Surveying

Magnetic declination

Angle between compassnorth (the direction the northend of a compass needlepoints) and true north (thedirection along the earth'ssurface towards thegeographic North Pole).

MD is positive if MN is at East of TN MD is negative if MN is at West of TN

TN (True North)

MN (Magnetic North)

TN (True North)

MN

MD = + MD (Magnetic Declination) = -

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Referencing


Vertical References

Depth References are of UtmostImportance

Hit the Targets!!

Avoid Collision!!

Mean Sea LevelReference

Ground Elevation

Water Depth

Sea Bed

RTE

RTE

TVD/Ref – True Vertical Depth

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Referencing


Vertical References – Onshore

Rotary Table Elevation

Ground Level

Well Head

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Referencing


Vertical References – Offshore


Mean Sea Level

Well Head

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Referencing


Vertical References – Offshore


Mean Sea Level

Well Head

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Wellhead Position


Overall Constraints – Well Objective

ExplorationThrow-away well (abandon after drilling)Look For Oil and Gas ReservoirsLook for Geological Structures

Appraisal Determine the extent of a discoveryIdentify boundariesMight be a keeper (used for production)

DevelopmentProductionInjection

Vertical Well (minimum deviation) Drilled over the target

Vertical Well (minimum deviation) Drilled over the targetUsually Side-Tracked

Minimise footage DrilledMinimise work over constraints

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Wellhead Position


Overall Constraints – Surface & Geological

Target(s) Location(s)Well to intercept more than one target

Topography (onshore or Sea Bed)

Geological ConstraintsShallow Gas PocketsNaturally DeviatedSalt DomesAvoidance of other geological features

Reduce Costs

Reduce/Simplify Engineering

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Wellhead Position


Overall Constraints

Land Locations

With land wells, the surface location of the well will usually be determined by the factors originallyprompting the decision to drill a deviated (as opposed to a vertical) well

Offshore Locations

Main difference between positioning a surface location on land and offshore is the number and proximity ofwellbores

Offshore platforms (between 6 and 60 wells, adjacent wells may have only 6' feet betweencentres).

Factors which directly affect the offshore site: water depth, bottom slope, sandy bottom versus coral reef,local currents, etc.

2. Positioning


End of Positioning

Next Chapter: 3. Well Profile Design

Questions?

2.positioning

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