Positioning POSITIONING AND COORDINATE SYSTEM The by IbrahimMassaad

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```									    POSITIONING AND
COORDINATE SYSTEM
The earth is an oblate spheroid
(a squashed sphere) and maps
are flat, which makes it difficult
to map the earth

Positioning

The earth is
divided into
latitude and
longitude
The equator is 0
degrees latitude
and poles are 90
degrees
The length of a
degree of latitude
is always the
same
Positioning
Meridians or lines of longitude run
from pole to pole
The equator is divided up into 360
degrees
The distance between meridians
changes depending upon the latitude
The prime meridian runs thru the
observatory at Greenwich, England
Longitude 0 to 180 degrees east and
west from that point
Positioning
Calculating the longitude and
latitude of a well on a map can
be very complicated
Rectangular grids have been
developed for use in surveying
A geodetic datum is a definition
of a model for the surface of the
earth

Positioning
An ellipsoid consist of:
A definition of an ellipsoid
A definition of how the ellipsoid is
oriented to the earth’s surface
A definition of the units of length
An official name
Region(s) of the earth’s surface for
which the datum is intended to be
used

Positioning
Datum 1927 is the most
commonly used datum for North
America
ED50 or European Datum 1950 is
the most commonly used datum
in the North Sea

Positioning
A map projection is a
mathematical formula which has
been designed to convert the
latitude/longitude method of
positioning to a flat map
With a flat map, wellbores can be
spotted with an X Y coordinate
system

Positioning
The most commonly used map
projection is the Universal
Transverse Mercator (UTM)
The Lambert map projection is
also common throughout the
world and is the most common
in the USA

UTM System
On most maps, the lines of
latitude and longitude are curved
intersections of these lines are
of different sizes and shapes,
which complicates the locations
of points and the measurement
of directions

UTM System
The UTM system tries to solve
this problem
The world is divided up into 60
equal zones, each 6 degrees
wide
The zones are from 84.5 degrees
North to 80.5 degrees south
Polar regions are covered by
other, special projections
UTM System

Each zone has
its own origin at
the intersection
of its central
meridian and the
equator
The zone is
flattened and a
square imposed
on it

UTM System

The outer edges
for the grid are
curved
The convergence
is the difference
between grid north
and true north
At the central
meridian, grid
north = true north

UTM System
Each of the 60 zones are
numbered starting with one at
the 180th meridian
The areas east and west of the
Greenwich Meridian are covered
by zones 30 and 31, respectively

UTM System
Points on the earth may be
identified by its zone number, its
distance in meters from the
equator (northing) and its
distance in meters from a north-
south reference line (easting)

UTM System
To avoid negative values of
eastings, the central meridian in
any zone is assigned the
arbitrary eastings value of
500,000 m
Along the equator a zone is
towards the polar regions
Eastings range in values from
approximately 200,000 to 800,000
UTM System

UTM System
For points north of the equator,
northings are measured directly
in meters, with a value of zero at
the equator and increasing
toward the north

UTM System
To avoid negative numbers in
the Southern Hemisphere, the
equator is assigned a value of
10,000,000 m and displacements
in the south are measured with
decreasing, but positive, values

UTM System
The well proposal is usually
derived from coordinates on a
grid system and therefore
directions will be referenced to
grid north
Directional surveys reference
true north
It may be necessary to convert
from one to another
Lambert System

The Lambert
Conformal Conic
Projection was
introduced by
Johann Lambert
in 1772
It is also called
the Conical
Orthomorphic
projection
Lambert System
Meridians are equally spaced
straight lines converging at one
of the poles
Parallels are unequally spaced
concentric circular arcs centered
on the pole of convergence
The cone is considered as
penetrating the earth along one
standard parallel and emerging
along another
Lambert System

The distance scale that applies to the
whole map is exact only at the
standard parallels

Lambert System
When used for maps of the
United States and individual
states, the standard parallels are
o        o
33 and 45 North
The Lambert Conformal Conic
official projection for the SPCS
(State Plain Coordinate System)
for states of predominantly east-
west expanse
Lambert System
A Transverse Mercator system was
used for states predominantly north-
south expanse
The state plane coordinate system is
the legal system used to survey on
land SPCS 27 and SPCS 83
The public land survey system is a
grid system used on land to locate
places on the earth

Public Land Survey
The most common
is the township
and range system
A principal meridian
and base line was
established
Supplementary
survey lines were
spaced at 24 miles
The 24 mile squares
were subdivided into
6 mile squares

Public Land Survey
The 6 mile squares are townships
going north and south and ranges
going east and west (in some places
a township is called a tier)
The township and ranges are divided
into sections
There are 36 sections to a township
and range
Section can be further broken down
into parts of a section
Public Land Survey

The public
land survey
system is not
extremely
accurate and
there are
differences
between true
north and
section lines
Public Land Survey
The survey data may be less
accurate than the land survey
and is +/- 0.5o azimuth at best

Public Land Survey
The original 13 states and some
states in the southwest (Texas) do
not use the township and range
system
They use the metes and bounds
system
In this method, lines are surveyed
along the irregular edges of the
property and the azimuth and lengths
of the lines recorded
Public Land Survey

There are no
references to a
national or
international
measurement
system