A DOWNHOLE WELL-OPERATION SYSTEM
Field of the invention
The present invention relates to a downhole well-operation system for operating
a driving unit and a logging tool downhole and transmitting well-logging data
from at least one logging tool to a surface data acquisition system by means of a
wireline. Furthermore, the invention relates to a downhole tool.
Background art
Modem petroleum drilling and production operations demand a great quantity of
information relating to parameters and conditions downhole. Such information
typically includes characteristics of the earth formations traversed by the wellbore,
along with data relating to the size and configuration of the borehole itself.
The collection of information relating to conditions downhole, which is commonly
referred to as "logging", can be performed using several methods.
In conventional oil well wireline logging, a probe, which is housing formation sen
sors, is lowered into the borehole when the well, or parts of the well, has been
drilled, and is used to determine certain characteristics of the formations t rav
ersed by the borehole. The upper end of the probe is attached to a conductive
wireline that suspends the probe in the borehole. Power is transmitted to the
sensors and instrumentation in the probe through the conductive wireline. Simi
larly, the instrumentation in the probe communicates information to the surface
by means of electrical signals transmitted through the wireline.
An alternative logging method is collecting data during the drilling process. Col
lecting and processing data during the drilling process eliminates the necessity of
removing or tripping the drilling assembly to insert a wireline logging tool. It consequently
allows the driller to make accurate modifications or corrections as
needed to optimise performance while minimising downtime.
Designs for measuring conditions downhole including the movement and location
of the drilling assembly contemporaneously with the drilling of the well have
come to be known as "measurement-while-drilling" techniques, or "MWD". Typically,
the downhole sensors employed in MWD applications are positioned in a cy
lindrical drill collar which is positioned close to the drill bit. The MWD system then
employs a system of telemetry in which the data acquired by the sensors is
transmitted to a receiver located on the surface.
There are a number of telemetry systems in the prior art which seek to transmit
information regarding downhole parameters up to the surface without requiring
the use of a wireline. Of these, the mud pulse system is one of the telemetry sy s
tems most widely used for MWD applications. The mud pulse system of telemetry
creates "acoustic" pressure signals in the drilling fluid which is circulated under
pressure through the drill string during drilling operations. The information ac
quired by the downhole sensors is transmitted by suitably timing the formation of
pressure pulses in the mud stream. The information is received and decoded by a
pressure transducer and computer at the surface. One problem with mud pulse
systems is the data transfer rate which for increased amounts of information be
comes insufficient.
An alternative to the mud pulse system is to use the wireline used to lower a log
ging tool into the borehole. Data transfer via a wireline has been developed by
using discrete multi-tone modulation (DMT). Such a system typically comprises a
surface transceiver, a cable and a downhole transceiver coupled to the surface
transceiver via the cable. The downhole transceiver communicates to the surface
transceiver using DMT modulation to transmit telemetry information over a set of
frequency sub channels allocated for uplink communications. The surface transceiver
may likewise communicate to the downhole transceiver using DMT modu
lation to transmit information over a set of frequency sub-channels allocated for
downlink communications. The number of uplink and downlink communications
sub-channels is preferably variable, and can preferably be changed depending on
the operating mode of the system. This allows additional sub-channels to be allocated
for downlink communications during programming and configuration of the
downhole equipment, and additional sub-channels to be allocated for uplink
communications during normal logging operations.
However, downhole operation becomes increasingly demanding in terms of supplied
power to a downhole operating system. The use of driving units for being
able to move around in the borehole, the use of one or several logging tech
niques in one downhole operating system and typically the use of several different
power tools to alter or maintain the well have increased the need for downhole
power significantly. When increasing the power supplied to a wireline, higher
data transmission voltages are needed for transmitting data by means of DMT
due to an increasing noise level stemming from an increased supply voltage.
Merely increasing the data transmission voltage in known systems leads to more
dissipated heat in the electronics of the data transmission system, which is a
common problem in downhole operation tools, since heat transfer can be pract i
cally impossible in a downhole environment. The increased dissipation of heat
limits the ability to transfer data at high rates while providing high power for the
downhole operation system in known systems.
Information is the key to being profitable in the oil and gas industry. The more
information one has regarding location and migration patterns of hydrocarbons
within a hydrocarbon reservoir, the more likely it is that that reservoir can be
tapped at its optimal location and utilised to its full potential. To this end, new
and more sophisticated sensor arrangements are routinely created and placed in
wireline probes, so much so that the information carrying capacity of traditional
wireline telemetry techniques are becoming inadequate. Also due to the in
creased need for power in downhole operation systems, it would be desirable to
have a communication technique which can support both high speed communica
tions between downhole sensors and a surface installation while providing a high
power to the downhole operation system.
Summary of the invention
It is an object of the present invention to wholly or partly overcome the above
disadvantages and drawbacks of the prior art. More specifically, it is an object to
provide an improved downhole operation system for operating a driving unit and
at least a logging tool, and to transfer data from the logging tool to the surface.
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 downhole well-operation
system for operating a driving unit and a logging tool downhole and transmitting
well-logging data from at least one logging tool to a surface data acquisition sy s
tem by means of a wireline, the system comprising:
- a surface transceiver,
- a wireline,
- a downhole transceiver,
- a logging tool, and
- a driving unit
wherein the downhole transceiver is coupled to the surface transceiver via the
wireline and communicates to the surface transceiver using orthogonal frequency
division multiplexing to transmit data via the wireline, and wherein the driving
unit and at least one logging tool is powered by the wireline by modulating a
Pulse Width Modulated (PWM) signal to the wireline by means of a transistor
bridge, while the driving unit and at least one logging tool is powered by the
wireline.
In an embodiment, the wireline may be a mono cable.
In another embodiment, a data transmission signal may be modulated by an a l
ternating signal voltage of preferably more than 30 volts, even more preferably
more than 40 volts, and even more preferably more than 50 volts.
Moreover, a modulating unit may be coupled to a power supply circuit by means
of a capacitive coupling.
In addition, the amplification of the transmitted signal may be Pulse Width Modu
lated by means of a transistor bridge.
In an embodiment, a modulating unit may be coupled to a power supply circuit
by means of a capacitive coupling.
Furthermore, a supply voltage applied to the wireline at the surface may be at
least 600 volts, preferably at least 800 volts, more preferably at least 1000 volts,
and even more preferably at least 1200 volts during a current draw of at least 4
amperes, preferably at least 6 amperes, more preferably at least 8 amperes, and
even more preferably at least 10 amperes.
Moreover, the wireline may be at least 10 kilometres long, preferably at least 15
kilometres long, and more preferably at least 20 kilometres long.
The invention furthermore relates to a downhole tool, wherein a signal voltage
may be Pulse Width Modulated by a transistor bridge.
Furthermore, a modulating unit may be coupled to a power supply circuit by
means of a capacitive coupling.
Finally, the voltage applied to the downhole tool may be at least 400 volts, pref
erably at least 500 volts, more preferably at least 600 volts, and even more pref
erably at least 700 volts during a current draw of at least 4 amperes, preferably
at least 6 amperes, more preferably at least 8 amperes, and even more prefera
bly at least 10 amperes.
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
illustration show some non-limiting embodiments and in which
Fig. 1 shows a downhole operation system according to the invention for downhole
operation and logging of well and formation characteristics,
Fig. 2 shows a schematic view of the data transmission between an uphole com
puter and a downhole operating system according to the invention,
Fig. 3 shows a schematic view of the data transmission steps using a wireline,
Fig. 4 shows an electrical diagram of a modulator circuit according to the inven
tion,
Fig. 5 shows a downhole operation tool according to the invention,
Fig. 6 shows a schematic view of a modulator circuit according to the invention,
and
Fig. 7 shows a cross-sectional view of a mono cable.
All the 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
Fig. 1 shows a downhole operation system 100 for operating a driving unit 5 and
a logging tool 4 and transmitting data from the logging tool 4 to the surface via a
wireline 2. A downhole tool string 6 is shown submerged into the well via a wireline
2 from a rig or vessel 101. The vessel 101 comprises a lowering means 103
in the form of a crane. The lowering means 103 is connected to a downhole tool
string 6 via the wireline 2 for lowering the downhole tool string 6 into the casing
102 of the borehole 104. Fig. 2 is a schematic view of the downhole welloperation
system 100 for operating a driving unit 5 and a logging tool 4 downhole
and transmitting well-logging data from at least one logging tool to a surface da
ta acquisition system 105 by means of a wireline 2. The system 100 comprises a
surface transceiver 1 for sending and receiving data via the wireline 2 to and
from a downhole transceiver 3 coupled to the surface transceiver via the wireline
2, wherein the downhole transceiver communicates to the surface transceiver by
means of orthogonal frequency division multiplexing to transmit data via the
wireline 2 by modulating a Pulse Width Modulated (PWM) signal to the wireline by
means of a transistor bridge, and while a signal voltage is pulse width modulated
(PWM) by means of a transistor bridge. This allows for simultaneous high power
and high data transmission through the wireline without risking high heat dissipation
downhole. The downhole tool string 6 comprises a driving unit 5 used to nav
igate the tool string 6 within the borehole 104 by means of wheels 51 engaging
the casing 102 of the borehole 104. The tool string 6 furthermore comprises a
logging tool 4 for logging characteristics information.
The logging tool 4 may log characteristic information on the formation surround
ing the borehole 104, information on the condition of the casing 102 of the bore
hole 104, or other downhole structures, such as valves or reinforcements of the
casing 102. The downhole operation system 100 comprises a driving unit 5 and
at least one logging tool 4, both powered by the wireline 2. Since time is a very
important factor when exploiting oil wells, especially off-shore oil wells due to an
extremely high cost of running oil rigs and vessels, operational time in the well
must always be considered very carefully. Working with power tools downhole,
such as cleaning tools, and navigating such tools in the borehole 104 by a driving
unit 5 is increasingly used and requires high power and thereby high voltages
provided for the downhole tool strings 6. Furthermore, several downhole logging
tools 4 for logging characteristics information on the formation surrounding the
borehole 104 or on the casing 102 are also widely used, and several ways of
transmitting data from such logging tools exist.
Changing between a tool string 6 comprising power tools and a tool string com
prising logging tools is time-consuming and very costly and should therefore be
avoided. Simultaneous operation of power-consuming tools while transmitting
logging data at a high transfer rate has been problematic due to increased levels
of noise when applying high voltages to the wireline 2. However, the use of or
thogonal frequency-division multiplexing (OFDM) modulation for transmitting da
ta via the wireline 2 according to this invention enables simultaneous high transfer
rate transmission of data and supply of high voltages. Therefore, a downhole
operation system 100 according to the invention is able to avoid the compromise
between data transfer rate and downhole power supply.
The driving unit 4 requires a high voltage to be able to operate satisfactorily, and
due to the high attenuation of the voltage applied at the surface when working
with very long cables typically more than 10 kilometres and in some instances
exceeding 15 kilometres, the supplied voltage at the surface must be high when
high voltages are required downhole. For instance, if 600 volts are required
downhole, 1200 volts may have to be applied at the surface due to attenuation.
Therefore, working with high voltages in a downhole operation system requires a
high supply voltage V2 at the surface, which as a consequence requires a high
signal voltage VI to ensure sufficient signal-to-noise ratio at high data transfer
rates. Therefore, a downhole well-operation system 100 according to the inven
tion may typically use a data transmission signal SI modulated by a high alternating
signal voltage VI, e.g. a signal voltage of 50 volts and a supply voltage of
1200 volts. If the required supply voltage V2 is lower, a lower signal voltage VI
can be sufficient and vice versa.
Fig. 3 shows a simplified schematic view of the use of a wireline 2 to transmit data.
The logging tool 4 provides a bit stream which is converted into an analogue
signal by means of electrical circuits comprising components, such as digital-toanalogue
converters (DAC), Quadrature Amplitude Modulators (QAM) and/or
Pulse Width Modulators (PWM), and the analogue signal is subsequently t ransmit
ted through the wireline 2. At the surface, the analogue signal is then received
from the wireline 2 and subsequently converted back into a digital bit stream by
means of electrical circuits comprising components, such as digital-to-analogue
converters (DAC), Quadrature Amplitude Modulators (QAM) and/or Pulse Width
Modulators (PWM), and the digital signal is subsequently transmitted to a pro
cessing means, such as a computer.
Fig. 4 shows a more detailed schematic view of a circuit according to the invention,
modulating the signal in the downhole tool string 6, which may be placed in
the logging tool 4 or elsewhere in the tool string 6 and be electrically connected
in one end to the wireline 2 and in the other end to the tool 4. The tool 4 is con
nected to a modulating circuit 300 through a tool interface 301 and a tool inter
face digital signal processor (DSP) 302. The tool interface DSP 302 is optionally
connected to the modulating circuit 300 through a universal asynchronous re
ceiver/transmitter (UART). The modulating circuit 300 comprises a modulating
DSP 303 connected to the tool interface DSP 302 for two purposes. First, when
receiving a signal from the tool 4, i.e. logged data, the modulating DSP 303
transmits (Tx) the inverse fast Fourier transform (IFFT) of the signal to transmitting
circuits 304 and further to a signal conditioning means 305 and again further
towards the wireline 2. Second, the purpose of the modulating DSP 303 is that
when signals are received (Rx) from the wireline 2, the signal from the wireline
passes through a receiving signal conditioning 308 to an amplifier 307 and is
converted by an analogue-to-digital converter (ADC). Subsequently, the received
signal is transformed by the modulating DSP 303 which uses fast Fourier t rans
form (FFT) ) and QAM symbol mapping to convert the signal into a bit stream of
the signal to the tool interface DSP 302 and further on to the tool 4 in order to
control the tool. The transmitting part 303, 304, 305 of the modulating circuit
300 may be connected in parallel with the receiving part 303, 306, 307, 308 of
the modulating circuit, as shown in Fig. 4.
Fig. 5 shows an embodiment of the modulating unit 400 comprised by a DC/DC
converter 401 which supplies a modulating voltage and a transistor half bridge
402 which is able to modulate a Pulse Width Modulated (PWM) signal to the wireline
2 by receiving a control signal from a transistor DSP 403. The modulating
unit 400 is protected from high supply voltage by a capacitive coupling 404. The
advantage of using a capacitive coupling 404 in this type of circuit is that the typical
alternative to the capacitive coupling is an inductive coupling. The inductive
coupling has the downhole disadvantages of dissipating more heat due to the
high current needed for the tool string 6 than the capacitive coupling 404, and
furthermore, an inductive coupling suited for high currents is bigger than the capacitive
coupling, which is also a disadvantage in downhole equipment. By using
a PWM modulated transistor bridge 402, the use of linear or near linear amplifiers
is avoided. Linear amplifiers are usually preferred when a very smooth signal is
required, such as in high-end audio amplifiers. However, the linear amplifier d is
sipates more heat than a PWM modulated transistor bridge, which is a disadvantage
in downhole equipment and especially when modulating high voltages,
which is required on long cables due to the high attenuation of the cable, such as
modulating a 600 volts supply voltage V2 with a 50 volts signal voltage VI modu
lating the supply voltage V2 from 575 volts to 625 volts using a transistor half
bridge 402. The transistor bridge 402 receives a PWM modulated control signal
from the transistor DSP 403. The signal voltage VI is provided by the DC/DC
converter 401 and grounded by a ground connection 406, such as a connection to
the casing or chassis of the tool 4.
When operating downhole with a downhole well-operation system 100 according
to the invention, the supply voltage V2 applied to the wireline 2 at the surface is
very high, preferably at least 600 volts, more preferably at least 800 volts, even
more preferably at least 1000 volts, and most preferably at least 1200 volts dur
ing a current draw of at least 4 amperes, preferably at least 6 amperes, more
preferably at least 8 amperes, and even more preferably at least 10 amperes.
This high voltage is needed in order to operate the driving unit 5, also known as
a well tractor. A well tractor is typically used to navigate a long tool string 6, such
as the one depicted in Fig. 6, comprising logging tools 4 and other tools, such as
stroker tools, cleaning tools, milling tools etc. and therefore requires an extensive
amount of power to operate all or several tools and the driving unit 5 simultaneously.
In an embodiment of the invention, the wireline 2 is at least 10 kilometres long,
preferably at least 15 kilometres long and more preferably at least 20 kilometres
long. The invention is particularly relevant when working with very long wirelines
2 due to the high attenuation of signals in long wirelines, which increases the
need for working with high voltages in order to obtain high power output downhole.
Fig. 6 shows a downhole tool 200 being attachable to a wireline 2 and comprising
a modulating unit 400 connected to a logging tool 4 and a driving unit 5.
Fig. 7 shows a cross-sectional view of a mono cable 21. The mono cable 2 1 comprises
an inner conductor 22 surrounded by a flexible, tubular insulating layer 24,
e.g. a Teflon layer, which is surrounded by an outer layer 25, often referred to as
a jacket or jacket layer. Exterior to the jacket 25, a tubular conducting shield
comprising a plurality of return conductors 23 is wound around the cable. The
tubular conducting shield is sometimes referred to as the armour of the cable
since it protects the cable. Furthermore, a mono cable, such as the one depicted
in Fig. 7, comprises two armour layers comprising a plurality of return conductors
23; one layer wound in one direction and one layer wound in the other (not
shown in Fig. 7), such that when the cable is twisted, one layer loosens and one
layer tightens simultaneously, which strengthens the cable. In other monocables,
a separate coaxial shielding layer acts as the return conductor. The use of mono
cables 2 1 offers some important advantages over multi-conductor cables when
working in a downhole environment. The mono cable 2 1 is widely used on oil and
gas exploitation facilities and therefore provides easy and cheap accessibility on
sites where a downhole operation system 100 according to the invention is intended
to be used. Furthermore, when exploiting offshore well-sites, and espe
cially deep-water well-sites, the safety of the well depends on pressure protection
between the borehole and seawater. This pressure protection typically comprises
a grease injector head for sealing off the well during wireline operations. The size
of the grease injector head is proportional to the thickness of the cable that
needs to be sealed off, and the thicker the cable, the more difficult it is for the
grease injector head to seal of the well, which in addition to the difficulties in
creases cost on both cable and grease injector head. Furthermore, a grease in
jector head leaks a portion of the grease into the sea environment, which is also
proportional to the thickness of the cable, and hence, a thicker cable leads to
more pollution of the sea environment.
By fluid or well fluid is meant any kind of fluid that may be present in oil or gas
wells downhole, such as natural gas, oil, oil mud, crude oil, water, etc. By gas is
meant any kind of gas composition present in a well, completion, or open hole,
and by oil is meant any kind of oil composition, such as crude oil, an oilcontaining
fluid, etc. Gas, oil, and water fluids may thus all comprise other ele
ments or substances than gas, oil, and/or water, respectively.
By a casing is meant any kind of pipe, tubing, tubular, liner, string etc. used
downhole in relation 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 kind of driving tool capable of pushing or pulling
tools in a well downhole, such as a Well Tractor®.
Although the invention has been described in the above in connection with preferred
embodiments of the invention, it will be evident for a person skilled in the
art that several modifications are conceivable without departing from the inven
tion as defined by the following claims.
Claims
1. A downhole well-operation system (100) for operating a driving unit (5) and
a logging tool (4) downhole and transmitting well-logging data from at least one
logging tool to a surface data acquisition system (105) by means of a wireline
(2), the system comprising:
- a surface transceiver (1),
- a wireline,
- a downhole transceiver (3),
- a logging tool, and
- a driving unit
wherein the downhole transceiver is coupled to the surface transceiver via the
wireline and communicates to the surface transceiver using orthogonal frequency
division multiplexing to transmit data via the wireline by modulating a Pulse
Width Modulated (PWM) signal to the wireline by means of a transistor bridge,
while the driving unit and at least one logging tool is powered by the wireline.
2. A downhole well-operation system according to claim 1, wherein the wire
line is a mono cable (21).
3. A downhole well-operation system according to any of the preceding claims,
wherein a data transmission signal (SI) is modulated by an alternating signal
voltage (VI) of preferably more than 30 volts, even more preferably more than
40 volts, and even more preferably more than 50 volts.
4. A downhole well-operation system according to any of the preceding claims,
wherein a modulating unit (400) is coupled to a power supply circuit (405) by
means of a capacitive coupling (404).
5. A downhole well-operation system according to any of the preceding claims,
wherein the amplification of the transmitted signal (SI) is Pulse Width Modulated
by means of a transistor bridge (402).
6. A downhole well-operation system according to any of the preceding claims,
wherein a modulating unit is coupled to a power supply circuit by means of a ca
pacitive coupling.
7. A downhole well-operation system according to any of the preceding claims,
wherein a supply voltage (V2) applied to the wireline at the surface is at least
600 volts, preferably at least 800 volts, more preferably at least 1000 volts, and
even more preferably at least 1200 volts during a current draw of at least 4 am
peres, preferably at least 6 amperes, more preferably at least 8 amperes, and
even more preferably at least 10 amperes.
8. A downhole well-operation system according to any of the preceding claims,
wherein the wireline is at least 10 kilometres long, preferably at least 15 kilome
tres long, and more preferably at least 20 kilometres long.
9. A downhole tool (200), wherein a signal voltage (VI) is Pulse Width Modu
lated by a transistor bridge.
10. A downhole tool, wherein a modulating unit is coupled to a power supply
circuit by means of a capacitive coupling.
11. A downhole tool, wherein the voltage applied to the downhole tool is at least
400 volts, preferably at least 500 volts, more preferably at least 600 volts, and
even more preferably at least 700 volts during a current draw of at least 4 am
peres, preferably at least 6 amperes, more preferably at least 8 amperes, and
even more preferably at least 10 amperes.