POSITIONING METHOD
Technical field
The present invention relates to a positioning method for determining the position
of a tool in a casing downhole.
Background
When running a tool in a casing downhole, it may often be desirable to know the
specific position of the tool. Especially when running different types of inspection or
logging tools, it may be very important to know the exact location of each observa
tion made during the inspection or logging. For this and several other reasons,
many attempts have been made to develop a device capable of determining the po
sition of the tool when situated downhole.
A known device for determining the position of a tool downhole is called a "Casing
collar locator". Typically, a locator comprises one or more magnets and one or more
coils for measuring changes in the magnetic and electrical flux when passing a col
lar or casing feature significant enough to cause a measurable change. The device
is thus only able to determine the position of the tool collar by collar and not be
tween two collars, and in order to measure differences in the flux, the device must
be moved with considerable speed in the casing.
Another "Casing collar locator" comprises one or more flux gate magnetometers in
the form of coils for measuring the remaining or naturally occurring magnetism in
the casing collars. However, in order to determine the position of the tool between
the collars, the wireline depth must be used.
As shown in US 6,768,299, a "Casing collar locator" may also comprise one magne
tometer for measuring changes in the strength of the magnetic field generated from
a magnet. The "Casing collar locator" may also comprise more than one magne
tometer to achieve different modes of detection so that one magnetometer detects
collars and the other magnetometers detect the direction of the tool in order to
control the direction of the drilling head of the tool.
Summary of the invention
It is an object of the present invention to wholly or partly overcome the above d is
advantages and drawbacks of the prior art. More specifically, it is an object to provide
an improved method capable of determining an exact position of the tool.
The above objects, together with numerous other objects, advantages, and fea
tures, which will become evident from the below description, are accomplished by a
solution in accordance with the present invention by a positioning method for determining
a position of a downhole tool moving in a casing in a well, comprising the
steps of:
- measuring a magnitude and/or direction of a magnetic field several times over a
time period by means of a first sensor comprised in the downhole tool, while mov
ing along a first part of the casing,
- determining a manufacturing pattern of the first part of the casing based on the
measurement, and
- determining a position of the downhole tool by comparing a reference manufac
turing pattern of the first part of the casing with the determined manufacturing pat
tern of the first part of the casing.
Furthermore, the position of the downhole tool may be determined from a point of
reference, such as a casing collar.
The positioning method may further comprise the steps of:
- determining a reference manufacturing pattern by measuring a magnitude and/or
direction of a magnetic field several times over a time period by means of a first
sensor comprised in the downhole tool, while moving along a first part of the casing
of a known length,
- estimating a wave length of the reference manufacturing pattern based on the
number of waves of the reference manufacturing pattern and the known length of
the first part of the casing having been measured, and
- counting the number of waves passing as the downhole tool moves along the first
part of the casing, starting from a point of reference,
wherein the position of the downhole tool is determined continuously with respect
to the point of reference as the downhole tool moves along the first part of the cas
ing, based on the number of waves counted and the estimated wave length.
Moreover, the positioning method may comprise the steps of:
- measuring a magnitude and/or direction of a magnetic field several times over a
time period by means of a second sensor comprised in the downhole tool, while
moving along the first part of the casing, the second sensor being arranged in the
downhole tool with an axial distance to the first sensor, and
- determining the velocity of the downhole tool along the first part of the casing
from a measured time period between the first sensor measuring a first point of the
casing and the second sensor measuring the same first point of the casing.
Furthermore, the positioning method may comprise the step of determining the velocity
of the downhole tool along the first part of the casing by comparing the
measurements from the first sensor with the measurements from the second sen
sor in order to calculate a velocity of the tool.
Additionally, the positioning method may comprise the steps of:
- measuring a magnitude and/or direction of a magnetic field several times over a
time period by means of the first sensor, while moving along a second part of the
casing,
- determining a manufacturing pattern of the second part of the casing based on
the measurement,
- determining the velocity of the downhole tool along the second part of the casing
from a measured time period between the first sensor measuring a first point of the
casing and the second sensor measuring the same first point of the casing, and
-comparing the manufacturing pattern of the first part of the casing and the manu
facturing pattern of the second part of the casing to determine the position of the
downhole tool to be able to adjust the determined velocity of the tool along the se
cond part based on the manufacturing pattern.
Furthermore, the manufacturing pattern of the first part of the casing and the man
ufacturing pattern of the second part of the casing may be compared by comparing
distinct marks of the to different manufacturing patterns to determine the position
of the downhole tool.
In addition, the casing may be made from metal.
The present invention furthermore relates to a positioning method for determining
a position of a downhole tool moving at a velocity in a casing in a well, comprising
the steps of:
- measuring a magnitude and/or direction of a magnetic field by means of a first
sensor several times over a time period while moving along a first part of the cas
ing manufactured from metal,
- determining a manufacturing pattern of the casing along the first part from the
measurement,
- measuring a magnitude and/or direction of a magnetic field by means of the first
sensor several times over a time period while moving along a second part of the
casing manufactured from metal,
- determining the velocity of the tool along the second part, and
- adjusting the determined velocity of the tool along the second part based upon
the manufacturing pattern.
The step of determining a manufacturing pattern may comprise determining a cycle
in the measurement coming when manufacturing the casing, such as forming the
casing by means of rolling, cold drawing, rolling milling.
Furthermore, the manufacturing pattern may be barrel or rolling lines in the casing.
In an embodiment, the casing may be connected by means of casing collars and
the first part and second part of the casing may be arranged between two collars.
Moreover, the first part of the casing may comprise several casing sections con
nected by collars.
Further, the manufacturing pattern may be thickness variations in the casing.
Additionally, the variation in the thickness of the casing may result from using a
non-circular roller when manufacturing the casing by rolling.
The manufacturing pattern may result from a rolling process, mill rolling, cold draw
ing or hot drawing.
I n addition, the sensors may be arranged in a detecting unit arranged in a tool and
comprising two magnets and two sensors arranged with an axial distance from each
other and in a same plane, such as on a plate.
Also, the manufacturing pattern may be a distance between a local minimum or
maximum thickness of the casing and a next local minimum or maximum thickness
of the casing.
Furthermore, the first sensor may have an axial distance to a second sensor and
the step of determining the velocity is from a measured time period between the
first sensor measuring a first point of the casing and the second detector measuring
the same first point of the casing.
Additionally, the variation of the thickness of the casing may result from a noncircular
roller used when manufacturing the casing by rolling.
The manufacturing pattern may be several fractions identified along the first part of
the casing.
Moreover, the method according to the present invention may comprise the steps
of:
- measuring the magnitude and/or direction of the magnetic field by means of the
second sensor, and
- comparing the measurements from the first sensor with the measurements from
the second sensor in order to calculate a velocity of the tool.
Said step of measuring the magnitude and/or direction of the magnetic field may be
performed several times over a time period, and the step of comparing the measurements
from the sensor may be performed after this time period.
The present invention also relates to a system for carrying out the method as de
scribed above, comprising:
- a detecting unit comprising two magnets and two sets of sensors arranged with
an axial distance from each other and in a same plane, such as on a plate.
By comprising two sets of sensors arranged with an axial distance from each other,
the positioning tool is able to estimate the exact position of the tool by counting the
number of waves of the manufacturing pattern and by continuously calculating the
velocity of the tool based on the manufacturing pattern. Hereby, the positioning
tool uses multiple methods to increase the accuracy of the position determination.
Also, the present invention relates to use of the method described above for accu
rately displaying a condition downhole in real time.
Finally, the present invention relates to use of the method as described above for
accurately displaying a position downhole in real time.
By accurately is meant that the displaying of the condition is more accurate than if
carried out by means of a casing collar locator.
Brief description of the drawings
The invention and its many advantages will be described in more detail below with
reference to the accompanying schematic drawings, which for the purpose of illus
tration show some non-limiting embodiments and in which
Fig. 1A shows a sequence of measurements by a sensor,
Fig. I B shows an enlarged view of part of the sequence shown in Fig. 1A,
Fig. 2 shows a positioning tool,
Fig. 3A show another sequence of measurements obtained by a sensor, and
Figs. 3B-3C show enlargements of a part of the sequence shown in Fig. 3A.
All these figures are highly schematic and not necessarily to scale, and they show
only those parts which are necessary in order to elucidate the invention, other parts
being omitted or merely suggested.
Detailed description of the invention
The present invention relates to a positioning method for determining a position of
a downhole tool moving at a velocity in a casing in a well, also between two casing
collars. When a downhole tool conducts certain measurements of the well properties,
such as the well flow, fluid characteristics, temperature, the pressure etc., the
measurements are each conducted at a certain time and position along the casing.
However, if the position is not accurate due to the fact that the tool moves at an
other velocity than expected, the measurements provide an inaccurate picture of
the well properties. When using present positioning tools, such as a casing collar
locator, the position is adjusted when the positioning tool passes a casing collar and
the distance since passing the previous casing collar is adjusted accordingly. How
ever, such adjustments presume that the tool velocity has been constant between
the previous and the present casing collar, and this may not always be the case.
When this happens, the measured well properties do not provide an accurate pic
ture of the well.
Using a positioning method according to the present invention, a magnitude and/or
direction of a magnetic field is measured several times over a time period by means
of a first sensor while moving along a first part of the casing manufactured from
metal, as shown in Figs. 1A and IB. The sensor is arranged in a positioning tool 1
comprising a detection unit 2, as shown in Fig. 2. The detection unit 2 comprises
two magnets 4 and two sets of r sensors 5, 6. These sensors 5, 6 are positioned so
that one sensor is positioned on each side of the magnet 4. The two sets of sensors
5, 6 are arranged with an axial distance d2 from each other and in the same plane
7, such as on a plate 8.
The positioning tool 1 has a substantially cylindrical shape, and the detecting unit 2
is arranged in its centre, extending along the length the tool. The plate 8 is fas
tened to the wall of the tool 1. When the tool 1 moves down the casing 3, the mag
netic field changes depending on the surroundings, and the sensors 5, 6 detect the
direction of the magnetic field lines when the tool moves. By performing substan
tially continuous measurements of the direction and/or magnitude, small variations
are measured while the tool 1 passes the part of the casing 3 between two collars
or joints, as shown in Fig. IB. The small variations in thickness result from the
manufacturing process, i.e. when the casing is made by means of rolling, resulting
in barrel lines or rolling lines in the casing. The measurements come from small in
accuracies in the diameter of the roller and results in a manufacturing pattern,
shown in Fig. IB, having peaks in the form of local minimums and maximums.
Each sensor 5, 6 measures the same changes, but there is a difference in time be
tween the measurements due to the distance between the sensors. The data from
the sensors 5, 6 is convoluted, and from the maximum value of the convolution, it
can be deducted when a sensor 5 of the first set of sensors passes the same posi
tion as a second sensor 6 of the second set of sensors, and so forth. The period be
tween the point in time when the first and the second sensor pass the same posi
tions is named , and since the distance d2 between the first sensor 5 and the second
sensor 6 is known, it is possible to calculate the velocity of the positioning tool
1 by means of the following equation:
The estimate of the velocity is based on a number of measurements, and by con
tinuously calculating the velocity of the tool 1, it is possible to calculate the distance
travelled since the previous calculation by means of the following equation:
where t is the time between calculations and is the estimated velocity. When
adding these estimated distances, the distance from the top of the well at a specific
time of e.g. an observation of an irregularity, such as a leak, is known.
Using convolution between datasets received from at least two sensors instead of
only comparing the measurements from one sensor with measurements from the
other measurement by measurement, the method is relatively insensitive to noise
in the measurements. I n this way, a more accurate result is obtained. Furthermore,
since the same characteristics are present in the two sets, the scale of the data is
not important.
When the tool 1 passes a joint or collar where two casing parts are mounted t o
gether, the change in field direction is substantially increased. At this point, the distance
from a collar is zero, and any errors in the estimated position of the tool can
be eliminated. The number of past collars and the distance from the last collar indi
cate the determined position of the tool since the distance between collars is
known. However, as mentioned, this determined position is based on the presump
tion that the tool moves at a constant velocity between two collars.
Fig. 1A shows a sequence of measurements conducted by means of a sensor mov
ing past two casing collars. Unfortunately, the sequence of measurements shows
the supports made of metal supporting the casing while testing, see the parts of the
measurements marked 51, and thus, the manufacturing pattern is thus only visible
at a distance from the supports and the collars. The part of the sequence of meas
urements conducted when the positioning tool passes a casing collar is marked 52.
Thus, the sequence of measurements showing the manufacturing pattern is marked
53 and is showed in an enlarged view in Fig. IB.
In Fig. IB, a pattern is identified as e.g. two distances X and Y which occur at a certain
point along the first casing part, and subsequently, this pattern is used to ad
just the velocity and thus the position of the tool between two collars. When mov
ing down the well, the positioning tool passes many casing parts between two col
lars, and thus, the manufacturing pattern is identified when the positioning tool
passing these first parts. The identified manufacturing pattern of the first casing
part may also be referred to as a reference manufacturing pattern. The pattern may
have a constant thickness change so that at a certain part of the casing, a distance
X between a local minimum or maximum thickness of the casing and a next local
minimum or maximum thickness of the casing is identified. Such constant thickness
variation may result from a non-circular diameter of the rollers used when manufacturing
the casing by means of rolling. Subsequently, when the positioning tool
passes a second casing part, another manufacturing pattern is identified, and any
variations in relation to the first identified manufacturing pattern or the reference
manufacturing pattern is used to adjust the velocity of the tool and thus correct the
position at which a certain measurement of a well property is conducted.
In another case, the manufacturing pattern is a more unique pattern since no con
stant thickness change is identified. However, a pattern identified as the same from
one casing part to the next when moving down the well also provides distinct marks
along a second casing part at which the determined velocity and position of the tool
can be adjusted by comparing the measured sequence of the second part of the
casing with the identified manufacturing pattern. The velocity and position of the
tool can thus be more accurately determined than would have been the case if car
ried out by means of a traditional casing collar locator since the tool velocity deter
mination is not only based on a sequence of measurements, but also on a comparison
of an expected and identified manufacturing pattern. Subsequently, the posi
tion of a measured well property can be more precisely determined.
The identified manufacturing pattern may only be fractions of the measurements
illustrating thickness variations of a casing part, and thus, the pattern does not
need to be identified along an entire casing part between two casing collars. By
having identifiable manufacturing pattern fractions along a casing part, these may
be used to adjust the determined velocity and position of the tool when measuring
a sequence of a magnitude and/or direction of a magnetic field by means of a sensor
while moving along a second part of the casing. When having e.g. two identified
manufacturing pattern fractions along a casing part, the velocity and position de
termined from the sequence of the magnitude and/or direction of a magnetic field is
adjusted twice along the second part and thus twice before reaching the next collar.
When producing the casing by means of rollers, the thickness of the casing varies in
a certain pattern which is identified and stored in the positioning tool as the ex
pected pattern and compared to the determined velocity. If the expected pattern
does not correspond to the measured pattern for determining the velocity of the
tool, the distance variations of the measured pattern in relation to the expected
pattern is determined and the measured pattern is adjusted accordingly, and the
velocity is recalculated or adjusted accordingly.
If the identified manufacturing pattern is a constant distance X between e.g. a local
maximum thickness of the casing and a next local maximum thickness of the casing
along the entire casing part between two casing collars, the tool velocity may be
adjusted based on the time elapsed between measuring a local maximum thickness
of the casing and a next local maximum thickness of the casing.
The detecting unit 2 of Fig. 2 only has four sensors 5, 6, and it is necessary to have
two of the sensors arranged on the same side of the magnets 4 to calculate the po
sition of the tool. The closer the two sensors 5, 6 are arranged in the longitudinal
direction of the tool, the faster the measurements can be processed. One magnet 4
can be arranged on the outside of a sensor 5, 6 so that the first magnet is arranged
on the outside of the first sensor and the second magnet is arranged on the outside
of the second sensor. When a magnet 4 is arranged on the outside of each sensor
5, 6, all sensors are positioned with the same distance to the magnet, which results
in a more precise measurement, again resulting in a better velocity estimates.
Thus, the positioning tool may comprise a first sensor 5 and a second sensor 6,
wherein the velocity is determined by measuring the magnitude and/or direction of
the magnetic field by means of the first sensor and subsequently the second sen
sor, and then comparing the measurements from the first sensor with the meas
urements from the second sensor in order to calculate a velocity of the tool.
In another positioning method according to the present invention, the manufact ur
ing pattern measured while moving along the casing is utilised in a slightly different
way. Figs. 3A-3C show sequences of measurement obtained by a sensor in a positioning
tool having been run through a section of casing. The positioning tool may
be a positioning tool such as that described above. The measurements show a
manufacturing pattern representing characteristics of the casing, such as material
characteristics as discussed above. The section of the casing having been scanned
in this specific example represents a length of approximately 70 feet. The meas
urements shown in Fig. 3A reveal three obvious features 52 which represent casing
collars present in the scanned section of the casing. In Figs. 3B and Fig. 3C, a sec
tion of the measurements shown in Fig. 3A is cut out and gradually enlarged. The
representation of the measurement shows that the manufacturing pattern resembles
a substantial periodic wave having peaks in the form of local minimums and
maximums, as described above.
The enlargement of the sequence of measurements shown in Fig. 3C represents a
length of a casing of approximately 3 feet and shows approximately 5 wave tops
56. Knowing the approximate length of the casing and the number of waves, the
wave length is estimated to approximately 7 inches in this specific example.
In a similar manner, the casing in an existing wellbore may be scanned, whereby a
reference manufacturing pattern is obtained. If the length of the scanned section of
casing downhole is known, the wave length of the reference manufacturing pattern
of the particular section of casing can be estimated based on the identified number
of waves. The length of a scanned section of casing may be known or estimated if
for example the section of the casing arranged between two casing collars or other
points of reference is scanned.
Subsequently, information about the wave length obtained from the reference
manufacturing pattern may be compared with another manufacturing pattern of the
same section of the casing determined through a subsequent run wherein the cas
ing is scanned. Knowing the wave length of the reference manufacturing pattern of
the section of the casing, the position downhole may be determined by counting the
number of waves identified as the positioning tool moves forward along the previ
ously scanned section of the casing Methods for counting the number of wave are
well known to the skilled person and may be conducted in an automated manner.
In theory, the number of waves may be counted from the top of the well to deter
mine the position downhole. However, factors such as variations in the manufactur
ing pattern of different sections of the casing or inaccuracies in the identification of
the number of wave may result in an undesirable inaccuracy in the position determined.
In practice, the number of wave may advantageously be counted from a
point of reference of a known position downhole. Such a point of reference may be
represented by a specific feature present downhole, such as a casing collar, a
valve, a nipple or a pop joint.
In one exemplary use, the method described above may be used for positioning a
downhole tool at a specific position along a section of a casing. The downhole tool is
moved through the well, e.g. using a downhole tractor, until a predetermined point
of reference is reached. Then, the positioning tool is activated and the manufacturing
pattern is determined, as described above. Depending on whether the specific
section of the casing has been scanned or logged before and whether a reference
manufacturing pattern exists, the specific position may be identified by simply
counting the number of waves as the downhole tool moves through the casing or
by first determining a reference manufacturing pattern and then counting the number
of waves from the point of reference. A reference manufacturing pattern for es
timating the wave length may be determined for a specific casing element prior to
inserting the casing element into the well, in an earlier run after the casing has
been installed or just prior to starting position estimation. Alternatively, a reference
manufacturing pattern may be determined for all casing elements individually, e.g.
for a casing from a specific manufacture, for casing elements from a specific batch,
etc.
The manufacturing pattern and the related variations in the magnetic filed detected
by the sensors may also result from material properties of the casing material or
other manufacturing processes such as mill rolling, cold drawing or hot drawing.
By fluid or well fluid is meant any type of fluid that may be present in oil or gas
wells, such as natural gas, oil, oil mud, crude oil, water etc. By gas is meant any
type of gas composition present in a well, completion or open hole, and by oil is
meant any type of oil composition, such as crude oil, an oil-containing fluid etc.
Gas, oil and water fluids may therefore all comprise other elements or substances
than gas, oil and/or water, respectively. The fluid may also be a combination of
gas, oil, water and small solids in the fluid.
By a casing is meant all types of pipes, tubings, tubulars etc. used downhole in re
lation to oil or natural gas production.
In the event that the tools are not submergible all the way into the casing, a downhole
tractor can be used to push the tools all the way into position in the well. A
downhole tractor is any type of driving tool capable of pushing or pulling tools in a
well, such as a Well Tractor®.
Although the invention has been described in the above in connection with pre
ferred embodiments of the invention, it will be evident for a person skilled in the art
that several modifications are conceivable without departing from the invention as
defined by the following claims.
Claims
1. A positioning method for determining a position of a downhole tool moving in a
casing in a well, comprising the steps of:
- measuring a magnitude and/or direction of a magnetic field several times over a
time period by means of a first sensor comprised in the downhole tool, while mov
ing along a first part of the casing,
- determining a manufacturing pattern of the first part of the casing based on the
measurement, and
- determining a position of the downhole tool by comparing a reference manufac
turing pattern of the first part of the casing with the determined manufacturing pat
tern of the first part of the casing.
2. A positioning method according to claim 1, further comprising the steps of:
- determining a reference manufacturing pattern by measuring a magnitude and/or
direction of a magnetic field several times over a time period by means of a first
sensor comprised in the downhole tool, while moving along a first part of the casing
of a known length,
- estimating a wave length of the reference manufacturing pattern based on the
number of waves of the reference manufacturing pattern and the known length of
the first part of the casing having been measured, and
- counting the number of waves passing as the downhole tool moves along the first
part of the casing, starting from the point of reference,
wherein the position of the downhole tool is determined continuously with respect
to the point of reference as the downhole tool moves along the first part of the cas
ing, based on the number of waves counted and the estimated wave length.
3. A positioning method according to claim 1 or 2, further comprising the steps
of:
- measuring a magnitude and/or direction of a magnetic field several times over a
time period by means of a second sensor comprised in the downhole tool, while
moving along the first part of the casing, the second sensor being arranged in the
downhole tool with an axial distance to the first sensor, and
- determining the velocity of the downhole tool along the first part of the casing
from a measured time period between the first sensor measuring a first point of the
casing and the second sensor measuring the same first point of the casing.
4. A positioning method according to claim 3, further comprising the steps of:
- measuring a magnitude and/or direction of a magnetic field several times over a
time period by means of the first sensor, while moving along a second part of the
casing,
- determining a manufacturing pattern of the second part of the casing based on
the measurement,
- determining the velocity of the downhole tool along the second part of the casing
from a measured time period between the first sensor measuring a first point of the
casing and the second sensor measuring the same first point of the casing, and
- comparing the manufacturing pattern of the first part of the casing and the manufacturing
pattern of the second part of the casing to determine the position of the
downhole tool to be able to adjust the determined velocity of the tool along the se
cond part based on the manufacturing pattern.
5. A positioning method according to any of the preceding claims, wherein the
determined manufacturing pattern results from thickness variations in the casing.
6. A positioning method according to any of the preceding claims, wherein the
determined manufacturing pattern results from a rolling process, mill rolling, cold
drawing or hot drawing.
7. A positioning method according to any of the preceding claims, wherein the
determined manufacturing pattern results from a distance between a local mini
mum or maximum thickness of the casing and a next local minimum or maximum
thickness of the casing.
8. A positioning method according to any of the preceding claims, wherein the
sensors are arranged in a detecting unit arranged in a tool (1) and comprising two
magnets (4) and two sensors (5, 6) arranged with an axial distance (d2) from each
other and in a same plane (7), such as on a plate (8).
9. A positioning method according to any of the preceding claims, wherein the
manufacturing pattern is several manufacturing pattern fractions identified along
part of the casing.
10. A positioning method according to any of the preceding claims, wherein the
casing is connected by means of casing collars and the first and second parts of the
casing are arranged between two collars.
11. A positioning method according to any of the preceding claims, wherein the
first part of the casing comprises several casing sections connected by collars.
12. A positioning tool for carrying out the method according to any of claims 1-
11, comprising:
a detecting unit comprising two magnets (4) and two sets of sensors (5, 6) a r
ranged with an axial distance (d2) from each other and in a same plane (7), such as
on a plate (8).
13. A positioning tool for carrying out the method according to any of claims 1-12.
14. Use of the method according to any of claims 1-12 for displaying a condition
downhole in real time.
15. Use of the method according to any of claims 1-12 for displaying a position
downhole in real time.