Wellbore surveillance system

Field of the invention

The present invention relates to a wellbore surveillance system for obtaining fluid reservoir information data, such as the position and quantity of gas, oil and/or water, while draining hydrocarbons from an oil or gas field via a casing in a wellbore in a formation, the casing having a vertical part near a top of the casing, the system comprising a first sensor for measuring a content of gas, oil and/or water in the formation, and a second sensor for measuring a content of gas, oil and/or water in the formation.

Background art

Conventional reflection seismology uses surface sources and receivers to detect reflections from subsurface impedance contrasts in order to obtain data of fluid reservoir information. The obtained image often suffers in spatial accuracy, resolution and coherence due to the long travel paths between source, reflector, and receiver. To overcome this difficulty, a technique commonly known as vertical seismic profiling was developed to image the subsurface in the vicinity of a borehole. By this method, a surface seismic source is placed in the drilling tool, and signals are received by a single downhole receiver or an array of downhole receivers within the same drilling tool. This step is repeated for different depths of the receiver (or receiver array). This is method used for drilling but is also suitable for obtaining fluid reservoir information data in the subsequent production optimising process.

Another known method is to arrange an array of seismic sensors distributed along jointed tubulars (e.g. drill pipe or coiled tubing) to determine the physical condition of the drill string and whether drilling may be optimised. The seismic sensors are configured to detect seismic energy imparted into the adjacent formation by a wellbore source or surface source. This method is used for drilling but is also suitable for obtaining fluid reservoir information data in the subsequent production optimising process.

In addition, an optical fibre can be arranged in the well in order to obtain temperature data of the fluid in the vicinity of the well but not fluid reservoir information data, such as the position and quantity.

Description 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 a method and system for obtaining fluid reservoir information data, such as the position and the amount of gas, oil and water, while draining hydrocarbons form an oil or gas field.

The above objects, together with numerous other objects, advantages, and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by a wellbore surveillance system for obtaining fluid reservoir information data, such as the position and amount of gas, oil and/or water, while draining hydrocarbons from an oil or gas field via a casing in a wellbore in a formation, the casing having a vertical part near a top of the casing, the system comprising:

• a first sensor for measuring a content of gas, oil and/or water in the formation, and
• a second sensor for measuring a content of gas, oil and/or water in the formation,

wherein the first and the second sensor are arranged at least partly in a casing wall of the casing, and the second sensor is arranged in a distance from the first sensor.

Having two sensors at a distance from one another makes it possible for one sensor to send out a signal in the formation and for the other sensor to detect the response from that signal. In this way, fluid reservoir information data can be obtained.

In one embodiment of the invention, the casing may have a second part more horizontal than the first part, and the sensors may be arranged in this second part.

By arranging the sensors in the second, more horizontal part, fluid reservoir information data can be obtained from a larger distance than with known measuring tools lowered into a well.

Furthermore, the system may have more than five sensors, preferably more than ten sensors, and more preferably more than twenty sensors.

In one embodiment, the first sensor may comprise at least one transmitter of a first signal, at least one receiver receiving the first signal and/or a second signal, and at least one transferring device, and the second sensor may comprise at least one transmitter of the second signal, at least one receiver the first signal and/or the second signal, and at least one transferring device.

When each sensor has a transmitter and a receiver, the system may still function if one transmitter or receiver in a sensor breaks down.

Furthermore, the first sensor may comprise a first and a second electrode for providing a current flowing from the first electrode to the second electrode to conduct a resistivity measurement or a conductivity measurement of the formation in order to determine the content of gas, oil and/or water in the formation.

Moreover, the sensor may comprise a microchip for transforming the signal or the resistivity or conductivity measurement into data and/or for storing and/or transferring the data, or for storing a representation of the data.

The present invention as described above may further comprise at least one tool comprising a communication device for receiving data from the transferring devices when the tool is in the casing.

Furthermore, the tool may comprise a driving unit, such as a downhole tractor.

In one embodiment, the tool may comprise means for making a cavity in the casing.

Moreover, the tool may comprise means for arranging a sensor in the cavity.

In addition, the transferring device and the communication device in the tool may use radio frequency for transferring data to the tool.

Moreover, the transmitter and the receiver of the sensor may be integrated as one unit.

Additionally, the transferring device may comprise a radio frequency identification tag, and the communication device may comprise a radio frequency identification reader.

In an embodiment of the invention, the sensor may comprise a battery for powering at least the transmitter and the receiver.

Furthermore, the tool may be connected with a wireline for powering the tool and for transmitting data to above the wellbore.

In addition, the tool may comprise a battery for powering the tool.

Moreover, the tool or the communication device may comprise a powering device for powering the sensor.

In another embodiment, the power device and the sensor may comprise an inductive coupling for transferring power from the tool to the sensor through induction.

Furthermore, the inductive coupling may be used for transferring data from the sensor to the tool.

Additionally, the sensor may comprise a processor for transforming the signal or the resistivity or conductivity measurement into data and/or for storing and/or transferring the data, or for storing a representation of the data.

In an embodiment, these signals may be generated by acoustics.

In yet another embodiment, the transferring unit in one sensor may have a wireless communication means for communicating wirelessly with another wireless communication means in another sensor or with a wireless communication means in a communication device arranged closer to the top of the casing.

Moreover, the system may comprise several communication devices arranged in a predetermined distance along the casing to the top of the casing, the distance being determined by the distance in which two devices are able to communicate wirelessly with each other.

In addition, the system may comprise several sensors with wireless communication means arranged in a predetermined distance along the casing to the top of the casing, the distance being determined by the distance in which two devices are able to communicate wirelessly with each other.

Furthermore, the invention relates to a downhole tool for reading the data of the sensors in the downhole system as described above, wherein the tool may comprise driving means, such as wheels, for driving the tool forward in the casing, and a communication device as described above.

Finally, the present invention relates to a method for installing the system as described above, comprising the steps of:

• providing a number of cavities at a distance from one another in the casing in the borehole, and
• arranging the sensors in the cavities.

The method may further comprise the step of positioning a tool downhole outside a sensor in order to transfer fluid reservoir information data from the sensor to the tool.

Finally, the method may further comprise the steps of loading power from the tool to the sensor, transmitting a signal by means of the transmitter or providing a current from the first electrode, receiving the signal by means of the receiver or receiving the current by means of the second electrode, transforming the signal or current into data, and transferring data from the sensor to the tool.

Brief description of the drawings

The invention and its many advantages will be described in further 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 wellbore surveillance system arranged in a casing downhole,
• Fig. 2 shows a sensor according to the invention,
• Fig. 3 shows another embodiment of the sensor,
• Fig. 4 shows yet another embodiment of the sensor,
• Fig. 5 shows yet another embodiment of the sensor,
• Fig. 6 shows yet another embodiment of the sensor,
• Fig. 7 shows a partial view of the system,
• Fig. 8 shows a partial view of another embodiment of the system, and
• Fig. 9 shows yet another embodiment of the system.

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 wellbore surveillance system 1 for obtaining fluid reservoir information data. When the formation 4 is drained of oil, the oil layer decreases, and the water becomes dominating. The oil runs up through a production casing 2, and eventually, the water will enter into the production casing and disturb the production of oil. In order to prevent the water from destroying the oil production, it is desirable to obtain information about the fluid reservoir and the amount and position of gas, oil and water while draining hydrocarbons from an oil or gas field. In order to be able to obtain such data, the system comprises at least two sensors 5. One sensor 5 sends out a signal 7 in the formation 4, and the response 29 is received by the other sensor or the same sensor. Having several sensors 5 makes it possible to obtain more detailed information about the reservoir by comparing the data from one sensor 5 with the data from another sensor. The system shown in Fig 1 comprises eight sensors 5 arranged with a mutual distance between them and spread out along the substantially horizontal part of the casing 2.

When the signal 7 passes the different layers of oil, gas and water, it changes, and these are the changes detected by the sensors 5 as a response. In order to analyse the data obtained by the sensors 5, a downhole tool 13 is lowered into the casing 2. The data is transferred from the sensors 5 to the tool 13, and when the tool reaches the surface, the data is analysed to obtain a profile of the layers of water, gas and oil.

The signal 7 transmitted is an acoustic signal, such as the signal used in seismic analysis. Seismic analysis pertains to waves of elastic energy, such as that transmitted by P-waves and S-waves, in the frequency range of approximately 1 to 100 Hz. Seismic energy is studied to interpret the composition, fluid content, extent and geometry of rocks in the subsurface.

The seismic data is analysed when it has been transferred from the tool 13 to an analysis system subsurface. The seismic data can be used for modelling geophysical attributes and shapes or a geologic causal model of all rock properties, such as temperature, pressure, velocity, viscosity, etc. Furthermore, the data can be used for determining petrophysical effects and for indentifying fluid traps, reserves, recovery and risk.

The tool 13 may also be connected with a wireline 16 by means of which the data is transferred to the surface. In this way, the tool can is able to stay in the casing over a longer period of time, even during production, and the data is sent to the surface almost immediately after it has been transferred to the tool 13. The tool 13 is powered by the wireline, but may also be powered by a battery 17.

As can be seen in Fig. 1, the tool 13 has wheels 23 for driving the tool forward in the casing 2, and when the tool reaches a position opposite a sensor 5, the data is unloaded. Subsequently, the tool 13 moves on to the next sensor 5 to unload data from that sensor and so forth.

The sensor 5 has a transmitter 6 for transmitting a first signal 7 and a receiver 8 for receiving the first signal. The receiver 8 in a first sensor 5 receives both the response of a signal 7 sent from the transmitter 6 of the first sensor 5 and the response of a signal sent from the transmitter of a second sensor. Furthermore, the sensor 5 comprises a transferring device 9 to be able to transfer data away from the sensor. The sensor 5 is arranged in the casing wall 30 in a bore. The sensor 5 is fastened in the bore by means of threads or snap-fit fasteners.

The sensor 5 of Fig. 2 is powered by the tool 13 when it is positioned opposite the sensor in the casing 2. While the tool 13 powers the sensor 5, the sensor is able to transmit and receive signals 7 to obtain fluid reservoir information, and the information received from the receiver 8 is transferred to the tool 13 as it is received by the receiver. Then, the tool 13 moves to the next sensor 5, and the operation is repeated.

The sensor 5 in Fig. 3 comprises a microchip 12, such as a microcontroller, for transforming the response received by the receiver 8 into digital data. The microcontroller comprises static RAM for storing the data. The sensor 5 comprises a transferring device 9 for transferring the data to the tool 13, which in this embodiment comprises an inductive coupling 19 matching an inductive coupling 20 of the tool 13 for transferring the data by means of inductance. The sensor 5 also has a battery 15 for powering the sensor over a period of time. In this way, the sensor 5 is able to perform measurements on the fluid reservoir without the tool 13 being present. The sensor 5 is programmed, e.g. by means of a timer, to conduct a measurement each time a predetermined period of time has passed and to store the data until it can be transferred to the tool 13 or another device.

As shown in Fig. 4, the sensor 5 comprises a wireless communication means 25 for communicating wirelessly with another sensor, the tool 13 or another communication device. The sensor 5 in Fig. 4 has two electrodes 10, 11 instead of a transmitter 6 and a receiver 8. The electrodes 10, 11 are used for resistivity or conductivity logging or measurements. When measuring the resistivity, a current is passed between the two electrodes, and the potential drops between them provide the resistivity of the fluid present in the formation 4. When measuring the conductivity, a current is induced in the formation, and the capacity to carry the current is observed. By resistivity or conductivity measurement is meant the response measured by the sensor 5, e.g. the capacity or the potential drop.

In Figs. 2-4, the sensor 5 is arranged in a through-hole in the casing 2, but the sensor may also be positioned in a cavity in the casing, as shown in Fig. 5. When the sensor 5 is arranged in only part of the casing 2, the sensor itself does not have to withstand the pressure difference between the annulus and the inside of the casing.

The sensor 5 of Fig. 5 comprises a battery 15, an inductive coupling 19 and a processor 21 in which the memory and a communication means in the form of an input/output interface are arranged. The inductive coupling 19 and the battery 15 may be arranged in one unit. The processor 21 may also comprise a radio frequency identification device (RFID) to be read by a radio frequency identification reader in the communication device 26 of the tool 13.

In Fig. 6, the system also comprises a valve 31, such as an inflow control valve, arranged adjacent to the sensor 5, enabling signals 7 from the sensor to close the valve if measurements show that the water layer is too close to the sensor and thereby the valve. In this way, the valve 31 is shut off before letting water into the casing 2.The tool 13 of the system 1 moves inside the casing 2 in order to read data from the sensors 5 and subsequently transfer the data to the surface. The tool 13 in Fig. 7 comprises wheels 23 for moving within the casing 2, but may as well comprise other driving means, such as a caterpillar track, legs or the like means. The tool 13 is powered through a wireline 16 for powering a motor driving a pump and thereby the wheels 23. The tool 13 comprises a communication device 14 for transferring data from the sensor 5. When the communication device 14 is positioned opposite the sensor 5, the data can be transferred.

The tool of Fig. 7 also comprises a powering device 18 for powering the sensor, if needed. If the sensor 5 does not have its own power, the tool 13 can transfer power to the sensor, which then performs a measurement, and the data is thus transferred to the tool 13 without being stored in the sensor first. In this way, the sensor 5 can be a very simple sensor with very few components. One way of transferring power to the sensor 5 is to use an inductive coupling 20 interacting with an inductive coupling 19 in the sensor 5. The power may also be transferred to the sensor 5 in another suitable way, such as by mean of microwaves, infrared light or lasers.

The tool 13 may also hold its own power by comprising a battery 17, as shown in Fig. 8. In this event, the tool 13 may stay in the casing 2 for a period of time when all the sensors 5 have been read several times and then emerge to the surface for data unloading. The legs holding the wheels 23 have been retracted in the tool of Fig. 8, enabling the tool to rest against the inner surface of the casing 2 and thus against the outer surface of the sensor 5. This facilitates more efficient transferral of data from the sensor 5 and/or power to the sensor. If needed, the tool 13 may have a connection means for providing a direct electrical connection with the sensor 5.

In Fig. 9, the system 1 comprises several communication devices 26 distributed along the casing 2 from the last sensor 5 to the top of the well. In this way, the wireless communication means 25 of the sensors 5 can transfer data to the next sensor or to the communication device 26 if the communication device is next in line. The communication device 26 then communicates the data to the next communication device and so forth until the data reaches to top of the casing 24 or well. By having the communication devices 26, a tool 13 is not needed for obtaining the data in each sensor 5.

In Fig. 1, the sensors 5 are arranged in the casing wall 30 so that only one sensor is arranged in the same circumferential plane of the casing. The sensors 5 may also be arranged in the same circumferential plane of the casing 2 and have a circumferential distance to one another, as shown in Fig. 9.

By fluid or well fluid is meant any kind of fluid which 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 oil-containing fluid, etc. Gas, oil, and water fluids may thus all comprise other elements 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 system is not submergible all the way into the casing, a downhole tractor can be used to push the system 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 invention as defined by the following claims.