GB2351305A

GB2351305A - Geological investigation using coiled tubing incorporating sensors

Info

Publication number: GB2351305A
Application number: GB0015301A
Authority: GB
Inventors: Philip Head; David Joseph French
Original assignee: WS Atkins Consultants Ltd; XL Technology Ltd
Current assignee: WS Atkins Consultants Ltd; XL Technology Ltd
Priority date: 1999-06-25
Filing date: 2000-06-21
Publication date: 2000-12-27
Also published as: GB0015301D0; GB9914786D0

Abstract

A method of deploying a geological investigation assembly to enable data to be transmitted to a receiving station above ground. The assembly consists of a length of coiled tubing having two tubes (20, 80) disposed coaxially and a transmission means for transmitting power or data from a number of sensors/transmitters (33), possibly of acoustic type. The sensors/transmitters (33) are disposed between the inner and outer coaxial tubing (20, 80) or in the flow path within the coiled tubing. There can be a means of penetration present, such as a drill or water jet (30, fig 2a, not shown). The assembly can be used on land or under the sea-bed. When used under the sea-bed the assembly can include a casing (35), which can be left beneath the sea-bed while the coiled tubing is detached.

Description

2351305 Underground Analysis The present invention relates to a method and

apparatus for investigating geological properties.

When assessing a sub-sea location for its suitability for oil production, it is important to consider the characteristics of the soil and rock. The types of soil and rock will affect the drilling of the well and the construction of the platform in a profound way. The characteristics of the seabed soils must also be considered in the design, construction and operation of structures founded on the seabed, and other construction work, such as oil pipes, cables anchorages and the like. Rock characteristics, both under the seabed and under land masses are also used for general prospecting and surveying.

A known system for gathering data involves drilling a borehole in a conventional way, removing the drill string, and then lowering analysis equipment into the borehole. It is time consuming and difficult, not merely to remove the drill string but to introduce the analysis equipment into the borehole. This is especially so where the location is in deep water, since the analysis equipment must be guided into the borehole, which is complicated by the swell of the sea, which causes the vessel to rise and fall relative to the seabed.

GB 2 243 173 A discloses a method of reducing this delay and difficulty. After having removed the drill string and drill bit, the drill bit is taken off the drill string, and the analysis equipment put on in its place.

The analysis equipment is then lowered into the borehole upon the drill string. At sea it is necessary to employ guidance means, adding to the cost and inconvenience.

The object of the present invention is to provide an apparatus for 5 investigating geological characteristics in an efficient manner.

According to the present invention there is provided a method of deploying a geological investigation assembly, to supply geological data to a receiving station above the ground, and installing the geological investigation assembly in the ground, the geological investigation assembly comprising; a length of coiled tubing, the coiled tubing including an outer tube and an inner tube disposed inside the outer tube and substantially coaxially with it, a transmission means for transmitting power and/or data to and/or from the receiving station, one or more sensors and/or signal transmitters, the sensors and/or signal transmitters being disposed substantially between the inner tube and the inner tube and the outer tube.

According to another aspect of the present invention, there is provided a method of deploying a geological investigation assembly, to supply geological data to a receiving station above the ground, and installing the geological investigation assembly in the ground, the geological investigation assembly comprising; 2 a length of coiled tubing, a transmission means for transmitting power and/or data to and/or from the receiving station, 5 one or more sensors and/or signal transmitters, the sensors and/or signal transmitters being disposed in the length of coiled tubing such that there exists a flow path through the coiled tubing.

Preferably the geological investigation assembly includes a penetration means.

The geological investigation assembly may be installed in tile ground of a sea bed, and the coiled tubing includes a disengagement means and a casing such that part of the coiled tubing can detach from the casing, leaving the casing beneath the sea bed as the remainder of the coiled tubing is raised.

According to another aspect of the present invention, there is provided a geological investigation assembly as defined above.

One or more geological investigation assemblies may be embedded in the ground to gain information about the geological structure beneath the sea bed. The term geological structure is meant in its widest sense, that is, to include the characteristics and composition of soil, rock and oil formations underground.

3 A geological investigation assembly and method of deployment and operation will now be described, by way of example, with reference to the drawings, of which; Figure I shows a geological investigation assembly being deployed from a vessel; Figures 2a and 2b show the geological investigation assembly in more detail; Figure 3 shows the deployment and interaction of two geological investigation assemblies.

Figure 4 shows the deployment and interaction of four geological 15 investigation assemblies.

Figure 5 shows an alternative deployment arrangement.

Figure 6 shows another method of installation. 20 Figures 7a to 7d show further embodiments of the investigation device.

Figures 8a and 8b show yet further embodiments of the investigation device, Figures 9a and 9b shows details of the installation of the device of figure 8.

Referring to Figure 1, a vessel 10 carrying the geological investigation assembly on board is positioned above the point of the seabed which is to be analysed. The assembly 26 is lowered from a gantry 14 upon the deck through a moonpool 15 in the vessel's hull. The assembly is suspended by a length of coiled tubing 20. This coiled tubing is stowed upon a nearby reel 12. The coiled tubing is fed off the reel and paid out by an injector on the gantry. The injector releases a sufficient length of coiled tubing for the geological investigation assembly to reach the surface of the seabed.

It is important that when the geological investigation assembly 26 is 10 introduced to the soil that the swell of the sea, and the consequent movement of the vessel, does not cause the assembly to be continually pulled upon in an erratic manner. Some method of heave control is provided to ensure that there is no unwanted movement of the penetration means relative to the sea bed.

Initially this may be provided by a compensation deck upon which the injector is mounted. Alternatively or additionally, there may be provided a telescopic joint in the assembly which, in response to signals from a weight indicator, extend or contract the joint. Anothcr method in which the assembly could be heave compensated is by attaching support ropes maintained at a constant tension (for example by securing the free ends of the ropes to moveable weights) to the coiled tubing, and allowing the coiled tubing above this point to flex without supporting the weight of the geological investigation assembly and any additional weight added to keep the gcological investigation assembly suspended vcrtically. Any or all these methods are suitable for maintaining a steady relationship between the penetration means of the geological investigation assembly and the sea bed.

Once the penetration means has caused soine of the geological investigation assembly to become embedded in the seabed, heave compensation may be carried out by more convenient methods. A buoyancy means 12 strapped to the coiled tubing applies an upward force to the length of coiled tubing between itself and the geological investigation assembly. The vessel does not have to stay directly above the point on the sea bed that it is wished to analyse once the geological investigation assembly has been correctly positioned. The coiled tubing above the buoys 12 assumes a curve to accommodate itself between the vessel and the buoys, whether the ship is rising and falling, or drifting horizontally away from the drilling position, proving that the length of coiled tubing above the buoys is of sufficient length to reach this far.

An alternative method of ensuring that the geological investigation assembly enters the sea bed vertically is to support the geological investigation assembly with a support frame, which is shown in figure 3.

Turning now to the geological investigation assembly itself illustrated in Figures 2a and 2b, the geological investigation assembly 26 includes a jetting nozzle 30, which is supplied by lubricating fluid such as water from the coiled tubing 22, this fluid removing the sand from in front of the jetting nozzle.

The coiled tubing comprises two coaxial tubes, that is, an inner tube 23 and an outer tube 24. The fluid is pumped from the vessel to the geological investigation assembly 26 by the inner coiled tube 23. A casing 35 is supported upon the inner coiled tubing 23, that is, the inner coiled tubing is threaded through the casing, and the casing pulled down into the exploratory hole upon the advancement of the jetting nozzle 30. As the 6 casing is introduced to the borehole 28, the fluid from the jetting nozzle, and the entrained soil, circulates back and up the borehole via the annulus between the casing and the coiled tubing, and continues via a controlled valve arrangement 32 up the annulus between the inner coiled tubing and an outer coiled tubing to the vessel, were the fluid may be filtered and recirculated. The controlled valve arrangement 32 allows the area to be choked back in the event of entering, for example, a gas pocket.

Embedded in the casing 35 are a series of acoustic transmitters 37 and receivers 38. In this embodiment they are distributed along the length of the casing in a regular, alternating fashion. A transmission line 40 is attached to the casing 35 (the transmission line being separate from the coiled tubing) which provides the necessary power to the sensors and receivers, and allows the transmission of data collected from the sensors up to the vessel, and control signals sent down from the vessel to both sensors and receivers.

The size of the geological investigation assembly, in particular its length, is dependent upon which property of the soil or rock beneath the sea bed that it is wished to study. For applications such as examining rocks around oil fields, the geological investigation assembly might typically be 1000 - 3000 rn in length, and have around 100 receivers and transmitters equally disposed along the entire length of the casing. If it is wished to examine only a short distance beneath the surface of the sea bed, for example in order to assess the structural properties of the sea bed, then the casing need only be a few meters in length.

When the casing has been installed at the correct depth, the coiled tubing is disengaged and raised to the surface vessel, leaving tile casing in 7 the borehole connected to the vessel by the transmission line. The jetting nozzle is sacrificed in this embodiment; but it could equally be designed to disengage from the casing and withdrawn together with the coiled tubing.

Rcferring to figure 3, after a first casing 35 has been installed, another geological investigation assembly 26' is installed (parts of the second geological investigation assembly, being similar to the first, shall be denoted with like reference numerals with the addition of a prime symbol) in a sea bed some distance from the first casing is embedded. This second geological investigation assembly includes a similar set of acoustic transmitters and receivers to the first geological investigation assembly, again disposed along a casing installed as the geological investigation assembly descends into the soil beneath the sea bed.

In a similar manner to the size of the geological investigation assembly, the distance between the two geological investigation assemblies will depend upon the particular application. For applications such as examining oil fields, the geological investigation assemblies might typically be 1 4 km. apart. For examination of only a short distance beneath the surface of the sea bed however, the distance need only be a few meters.

The same length of coiled tubing, and hence the same reel, gantry, moonpool, injector and heave compensation means may be used for both geological investigation assemblies. The two transmission lines may be connected to the vessel at any convenient location.

An acoustic signal is transmitted from one or all of the first geological investigation assembly's transmitters, to be picked up by the receivers of the second geological investigation assembly. Usually, each 8 transmitter upon the casing will send a signal in sequence along the casing, the signals being of the same frequency. From the changes occurring in the transmitted signal, deductions may be made about the structure of the soil using a conventional method. If desired, the process may be repeated using the second geological investigation assembly to transmit a acoustic signal, to be picked up by the first, to gain further seismic data. It will be appreciated that in general a single signal from a transmitter on one geological investigation assembly will generate responses from every sensor on the other geological investigation assemblies, so for four assemblies each having 100 transmitters and receivers, 120,000 plots would be generated.

As shown with the geological investigation assembly 26' on the right hand side of the figure 3, the coiled tubing 22' does not have to be disconnected from the casing in order to operate the casing. This is most likely to be relevant for the last geological investigation assembly of a series to have been installed.

Referring to figure 4, a number of similar geological investigation assemblies 26,26' may be installed in boreholes 28, 28', 28%28 beneath the sea bed, aiTanged in a rectangular array. In the drawing, four geological investigation assemblies are shown, although there may of course be more.

Each geological investigation assembly may then be operated to transmit an acoustic signal form its transmitters in the sequential manner described above. The data received from the receivers of all the geological investigation assemblies (except normally the one which has just broadcast) is then logged for processing.

9 Referring to figure 5, the investigation assemblies may enter the ground at or near a single point. In this embodiment, the penetration means of the investigation assemblies is a drill bit including directional drilling means, so that after an investigation assembly has entered the soil, its course becomes more horizontal. Several investigation assemblies installed this way fan out radially, so that a signal from one or more transmitters on one investigation assembly may be received by neighbouring investigation assemblies by a direct path, or reflected from some underground feature. The signals are sent to the vessel 10 along the transmission line or lines 40.

The transmittal of signals may be prompted by control signals received from the vessel. There are several known methods of analysing such seismic data. Using three or more geological investigation assemblies installed in this way allows a good three-dimensional image of the characteristics of the soil beneath the sea bed to be built up. It will be realised that since the investigation assemblies are not fully vertical in this embodiment, the depth of the assemblies will be less than would be the case if fully vertical. A typical range for such an arrangement could be 300 600 metres.

The transmission line of a geological assembly includes a weak point close to its point of attachment to the casing. When a sufficient amount of data has been gathered, and it is decided to end the seismic tests and move the vessel away from the site, the transmission line will snap at the weak point and the majority of the length of the transmission line may be retrieved. Alternatively, a buoy could be attached to the tipper end of the transmission line, so that the casing may be located and connected to the vessel for subsequent seismic tests. Other guiding means could be left at the hole to enable the user to return to the casing.

Investigation of underground features such as the soil characteristics, geological structure, oil formations, and the like, from a land based (as opposed to sea bed) site are amenable to the same techniques. In such a case, figure 4 shows assemblies 26 introduced from installation rigs set 5 upon the ground 90 above the bore hole openings 28.

Referring to figure 6, a length of coiled plastic inner tubing 20 oil a reel is mounted upon the ground. Outer tubing has already been installed in a pre-drilled borehole 80. The inner coiled tubing is unreeled and introduced to the outer tubing by a guidance and injector means 41. A weight is suspended from the end of the inner tube; this weight holds the inner tube under tension, increasing its length and decreasing its diameter so that it may pass onto the outer tubing. Two reels of cables 33 are positioned either side of the inner tube as it is injected into the well 80. The cables include sensors and/or transmitters at regular intervals. As the inner tube 50 is lowered into the outer tubing 20, the cable and sensors 33 are applied (for example with some adhesive means) to the inner tube along the inner tube's length. When the inner coiled tubing 50 is fully unwound, the weight 31 is released from the inner tube. The inner 50 tube elastically contracts, and its diameter increases, so that it becomes fixed in the outer tubing 20, with the sensors 33 secured between the inner and outer tubes.

The sensors could of course be secured on the inner tube in a separate operation prior to the installation of the inner tube in the outer tube. The sensors and the line of cable could be wrapped around tile inner tube in a helical fashion. The inner tube and outer tube can be secured in other ways, for example the application of a deforming pressure to one or other of the tubes. The inner tube could for instances be swaged in order to increase its diameter., or the outer tube crimped to decrease its diameter, and so secure the tubes together, and so secure the sensors and their cabling in position between the tubes.

Figures 7a to 7d show further possible embodiments of part of the investigation assembly. Within the diameter of the coiled tubing 20 is included a one or more sensors, which typically will be distributed along the length of the coiled tubing. Each sensor 57 includes cabling 55 to supply the sensor with power, and to carry away received data. An inner coiled tubing 50 may be included in the coiled tubing, and, as shown, flow paths may be provided by the bore of the outer coiled tubing and/or the bore of the inner tube. Cement may be pumped down the bores of the inner tube and the outer tube to improve the sensing and transmission of acoustic signals. Cabling 52 (including power and data cables) to link the sensors to the surface (ie the vessel, rig or land base) may be wrapped around the inner tube if present.

Referring to figures 8a and 8b, plurality of sensors 72 is mounted linked by a cable 74 (which leads to the surface station as discussed above). The cable and sensors may be installed as suggested above, or set flush with the inner tube. Two such lines are mounted on the inner tube 70 in a diametrically opposing manner. As shown in figures 9a and 9b, the inner tube is introduced into the outer coiled tubing 20, and soil penetration means attached as in the former examples. Apertures 76 are included at intervals in the wall of the outer coiled tubing 20, and corresponding apertures 76 in the wall of the inner coiled tubing, these apertures, like the sensors, being positioned in a diametrically opposing manner, but positioned 90' from the sensors about the radius of the cross section of the inner and outer tubes. These apertures permit oil from an oil formation to enter the coiled tubing and inner tube, so that the sensing system can be 12 used to recover oil, either for analysis purposed, or for oil production purposes. The sensors, being positioned away from the apertures, and sandwiched between the outer tube and the inner tube, are protected from possible damage.

Many variations will be apparent to one skilled in the art. The transmission means to the vessel may be effected by a remote signalling device, such as an acoustic signal, for instance. Various penetration means may be substituted for the jetting nozzle, for example, a drill bit (powered either electrically or by pumped fluid), a hammer bit, or a vibrating nose cone.

Other sensors and transmitters, of which there are many known types, could be included in the casing instead of or apart from the acoustic receivers and transmitters.

Other sensors or receivers of transmitted seismic signals or the like could be incorporated in an arrangement of geological investigation assemblies according to the invention. Thus, an acoustic transmitters deployed in an existing well shaft could send and receive acoustic signals to and from a geological investigation assembly herein described.

Further sensors, such as high energy sensors, may be introduced into the coiled tubing through the flow path. This may be done before the investigation assembly is embedded in the ground, or the additional sellsors may be introduced afterwards. The position of the sensors may be conveniently altered, for example, by allowing them to descend upon a cable on the one hand, and pulling them upwards on the other hand.

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Claims

1. A method of deploying a geological investigation assembly, to supply geological data to a receiving station above the ground, and installing the geological investigation assembly in the ground, the geological investigation assembly comprising; a length of coiled tubing, the coiled tubing including an outer tube and an inner tube disposed inside the outer tube and substantially coaxially with it, a transmission means for transmitting power and/or data to and/or from the receiving station, 15 one or more sensors and/or signal transmitters, the sensors and/or signal transmitters being disposed substantially between the inner tube and the inner tube and the outer tube. 20

2. A method of deploying a geological investigation assembly, to supply geological data to a receiving station above the ground, and installing the geological investigation assembly in the ground, the geological investigation assembly comprising; 25 a length of coiled tubing, a transmission means for transmitting power and/or data to and/or from the receiving station, 14 one or more sensors and/or signal transmitters, the sensors and/or signal transmitters being disposed in the length of coiled 5 tubing such that there exists a flow path through the coiled tubing.

3. A method according to either previous claim, wherein the geological investigation assembly includes a penetration means.

4. A method according to any previous claim, wherein the geological investigation assembly is installed in the ground of a sea bed, and the coiled tubing includes a disengagement means and a casing such that part of the coiled tubing can detach from the casing, leaving the casing beneath the sea bed as the remainder of the coiled tubing is raised.

5. A method according to any previous claim, wherein the sensors and/or signal transmitters include an acoustic transmitter.

6. A method according to any previous claim, wherein the sensors 20 and/or signal transmitters include an acoustic receiver.

7. A method according to any of claims I to 4, wherein the sensors and/or signal transmitters include both an acoustic receiver and an acoustic transmitter.

8. A method according to any previous claim, wherein cement is introduced along the coiled tubing.

9. A inethod according to any previous claim, wherein at least two geological investigation assemblies are within sensing and/or transmitting range of one another.

10. A method according to any previous claim, wherein the transmission means is a transmission line unattached to the coiled tubing.

11. A method according to claim 10, wherein the transmission line includes a weak portion adapted to break when subjected to a sufficient 10 force.

12. A rnethod according to any of claims 2 to 11, wherein one or more sensors are introduced to the coiled tubing through the flow path.

13. A method according to any previous claim, wherein the penetration means comprise a fluid jet means.

14. A geological investigation assembly according to any previous claim.

15. A method of deploying a geological investigation assembly substantially as herein described and illustrated.

16. A geological investigation assembly substantially as herein described and illustrated.

17. Any novel and inventive feature or combination of features specifically disclosed herein within the meaning of Article 4H of the International Convention (Paris Convention).

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