A METHOD OF ABANDONING A PETROLEUM WELL

The present invention relates to a method of abandoning a petroleum well. More particularly it concerns a method of abandoning a petroleum well which is provided with at least one measuring device arranged for communicating measuring results to a receiver device by means of a communication means extending between the measuring device in the well and the receiver device located at a surface of the well.

In connection with search and exploration for and possible production from hydrocarbon reservoirs under the earth surface, petroleum wells are drilled. When some of, or all the mentioned activities are completed, a petroleum well, hereinafter called "well" may be abandoned.

To be able to abandon a well there are requirements regarding protection of the well against fluid leaks through the well and up to the surface. Such protection of a well may be temporary or permanent. A person skilled in the art will know which barriers are required for a temporarily protected well and for a permanently protected well.

Even if a well is abandoned, it will be of great value to be able to perform measurements in the well and in the reservoir. This is to be able to collect information on possible changes in such as pressure and temperature in the well and the reservoir. Such measurements can give valuable informa-

tion about such as stabilised temperature in the reservoir and from reservoir to the sea bed, development regarding pressure in the reservoir, so-called pressure communication with another well or other wells in the area, distances to geologic faults in the underground and extension of an area with producible hydrocarbon volumes .

Additionally it might be useful to collect information about pressure across barriers in the well and thereby obtaining knowledge about the barrier integrity. Such barriers may for example be, but are not limited to, mechanical plugs, cemented sections, chemical products and gravel pack materials. By the notion cemented in this context is meant a seal obtained by a liquid seal material filling a space and then transforming to the solid state.

For safety reasons authorities, among others, require that a protected well has several, independent barriers.

A well comprises typically a composite casing where more casings having different diameters are located one inside the other. Well piping is installed in the casing as needed. Ex- amples of such well piping are drill pipe and production tubing.

A single casing or a composite casing, which may also comprise other piping such as liner, are below called casing. The casing typically extends down into the ground from a wellhead, which as a submerged well is concerned is located above the seabed.

According to prior art a well in the ground is permanently protected by removing the upper portion of the well. This is done by a rig vessel, which firstly is brought in over the well and pulls at least a portion of the production piping out of the well. The casing is thereafter cut below the sea-

bed by means of a cutting tool . After the casing has been cut, the cutting tool is removed from the well whereafter the rig vessel lifting equipment is connected to the casing and lifts the upper cut casing portion out of the well.

The method according to prior art calls for the utilisation of relatively large vessels equipped with drilling equipment, and these are, among other things, due to repeated connection to the well, relatively time consuming and costly.

Another considerable drawback with prior art cutting of the casing is that, in addition to the casing itself, any cable also running inside the casing will also be cut. Communication via a cable such as a signal transmission cable or a well pipe, between for example a sensor in the well and a receiver device located above the cut location, will thus not be possible after cutting of the casing. A person with knowledge in the art will be familiar with that the alternative to communication via cable, so-called wireless communication, has a limited range. Wireless communication will in most cases thus not be suitable for wells stretching far, for ex- ample 2000m into the earths crust.

The object of the invention is to remedy or reduce at least one of prior art drawbacks .

The object is achieved by features given in the below description and in the following Claims.

The present invention relates to a method of abandoning a petroleum well which is provided with at least one measuring device by means of which a communication means is provided to be able to communicate measured results to a receiver device located at a surface of the well, where the method comprises termination of the communication means in a first communication coupling located in a portion of the well above an upper

well barrier, so that the receiver device being provided witt a fourth communication coupling which complementary fits with said first communication coupling, may selectively be connected to or disconnected from the measuring device for com- munication of data out from the well.

In one embodiment the communication means is constituted by a signal transmission cable or "lead" .

In one embodiment the communication means is constituted by a well pipe where data or measured results from the measuring device are transmitted through the well pipe, for example by means of sound waves. A person with knowledge in the art will appreciate that the signals from the measuring device then need to be transferred to the well pipe by means of a sound wave generating device and that the receiver device need to be arranged to be able to intercept the sound waves transmitted through the well pipe material.

Further features of the method according to the present invention are given in the following description and in the Claims 3 and 5-15.

The at least one measuring device may be provided by a single or more spaced measuring devices such as sensors, or it may be provided by such as a fibre optical cable or semi rigid rod of the type described in Norwegian Patent Application NO 20065913 handed in by the present applicant and which is in- corporated in this document by reference.

In those cases where the communicati_-i means are provided by a signal transmission cable or lead, the signal transmission cable extending between the at least one sensor and the terminal point is located to a well pipe located in the well. The well pipe may be, but is not limited to, such as a production tubing.

Advantageously, the signal transmission cable and any other leads or cables are, at least partly, placed in an enclosure attached to or integrated in the well pipe. The enclosure will inter alia be able to reduce the risk of fluid leaking through a barrier, where the barrier is provided by means of a fluid transforming to solid state. A cement plug is an example of such a barrier. Leaks may occur in such barriers due to insufficient packing of the barrier between lead(s) and well piping.

In the following is described an example of a preferred embodiment illustrated in the attached drawings, where:

Fig. 1 shows a well where several casings extend from a wellhead at the surface and where a well pipe provided with settable packers is led into the well;

Fig. 2 shows a temporarily abandoned well where the well pipe is terminated in the well and where settable packers and internal well barriers are set;

Fig. 3 shows the same as figure 2, bur where a measuring device in the form of a data logger is connected to an upper portion of the well pipe in order to be able to receive, via a signal transmission cable or lead placed on the outside of the well pipe, signals or data from sensors located in the well ;

Fig. 4 shows the well in fig. 2, but where a cementing pipe is connected to the upper portion of the well pipe and where the internal top well barrier Las been removed and a sealing substance is circulated into a lower portion of the well by means of a lower circulation valve;

Fig. 5 shows the well in fig. 4, but where sealing sub- stance is placed in three zones in the well and where the ce-

meriting pipe and an upper portion of the well pipe is disconnected and removed from a lower portion of the well pipe;

Fig. 6 shows the well in fig. 5, but where a part of the wellhead is removed; whereafter recesses are formed in the inner casing and where sealing substance is introduced in a portion of the annulus between the two innermost casings;

Fig. 7 shows the well in fig. 6, but where the whole wellhead is removed and the casings cut below the seabed, after which the upper well pipe section once more is connected to the lower well pipe section; and

Fig. 8 shows the well in fig. 7, but where a data logger is situated at an end portion of the upper well pipe section.

In *"he figures, that a person with knowledge in the art will appreciate are only principle sketches, the reference numeral 1 relates to a well lined with several casings 3 placed one inside the other. The casings 3 extend from a surface 5 being such as a seabed. A wellhead 7 is placed on the seabed 5 over the casings 3.

A well pipe 9 is placed in the well 1. In the example of the embodiment shown, the well pipe is a production tubing.

The well pipe 9 includes an upper barrier 11 and a lower barrier 13 where both may be set to seal an annulus between the well pipe 9 and the innermost casing 3. This annulus is known as the "A-annulus". The settable barriers or packers 11, 13 may be activated/deactivated in a wa" known per se.

The well pipe 9 is further provided with an upper circulation valve 15 and a lower circulation valve 17 arranged to be able to circulate a sealing substance 19 (see fig. 5) into the well 1 to provide a so-called permanent barrier in the annu-

lus between the well pipe 9 and the casing 3 and internally in the well pipe 9.

The well pipe 9 further consists of an upper well pipe section 9a and a lower well pipe section 9b. The upper well pipe section 9b is defined by a first coupling device 91 and a second coupling device 92 located in an upper and a lower end portion respectively of the upper well pipe section 9a. The second coupling device 92 is arranged to be able to be connected to a complementary fitting third coupling device 93 positioned in an upper end portion of the lower well pipe section 9b. Correspondingly, the first coupling device 91 is arranged to be able to be connected to a pipe or other equipment provided with a complementary fitting fourth coupling device 94. In the figures the first and the second coupling dev_jes 91, 92 are shown as so-called female or box connectors, while the third and fourth coupling devices 93, 94 are shown as so-called male or pin connectors. Which of the connectors 91, 92, 93, 94 being pin connectors and which are box connectors is of no significance for the invention as long as said connectors fit complementary together.

The coupling devices 91, 92, 93, 94 are controlled in a way known per se by means of for example, but not limited to, electricity or hydraulics. Advantageously the coupling devices are made with arrangements (not shown) making connec- tion to for example a lifting tool (not shown) possible.

On the outside of the well pipe 9 are placed two measuring devices or sensors 21, one at the to] of the lower barrier 13 and one at the top of the upper barrier 11. The sensors 21 are connected to a signal transmission cable or lead 23 run- ning along the outside of the well pipe 9. The leads 23 are allocated to communication connectors or contacts 91', 92' and 93' placed in the coupling devices 91, 92 and 93 respec-

tively. Depending on the function of the pipe or equipment of the fourth coupling device 94, this may be provided with a communication connector or contact 94 '. A receiver device 29 would for example have to be provided with a contact 94' placed in the coupling device 94 if it shall be able to be connected to the lead 23 ending in the contact 91' placed in the first coupling device 91.

For the sake of clarity, the reference numerals for the contact devices 91', 92', 93' and 94' are only given in figure 1.

Portions of the well pipe 9, above the circulation valves 15, 17, are provided with cable ducts 25 arranged to be able to receive such as the lead 23 and any other cables (not shown) . The cable ducts 25 reduce the risk of fluid leaks up through the interface area between the lead 23 and any other cables and the well pipe 9. Experience shows that that it is very difficult to achieve adequate packing of sealing substance 19, such as concrete, in this area. The cable ducts 25 are made with transition without acute angle against the outer surface of the well pipe 9. Preferably the cable ducts 25 are filled inside with a suitable sealing substance (not shown) after the lead 23 and possibly any other leads are pulled through .

The well pipe 9 is also provided with a so-called centraliser unit 12 which design and function will be known to a person with knowledge in the art and which for that reason is not discussed further in this document. irther details of the well pipe shown, but not given reference numerals or closer description in this document, will also be well known to a person with knowledge in the art.

In figure 1 is shown an open well 1 wherein the upper well pipe section 9a of the well pipe 9 is connected to a connecting pipe 9c by means of the first 91 and fourth 94 coupling device. The connecting pipe 9c extends up through the well- head 7 and for example a rig (not shown) on a sea surface (not shown) .

In figure 2 the well is temporarily abandoned. The upper barrier 11 and the lower barrier 13 are set such that a portion of the annulus between the lower well pipe section 9b and the casing 3, the so-called "A-annulus", is isolated. Internal flow within the well pipe 9 is prevented by means of internal barriers or packers 27. The internal packers 27 are of a type known per se and are therefore not discussed further in this document. The connecting pipe 9c shown in figure 1 is discon- necked from and removed from the upper well pipe section 9a.

In figure 3 a logging unit 29 is connected to the upper well pipe section 9a by means of the first coupling device 91 and a coupling device 94 corresponding to the coupling device 94 for the connecting pipe 9c shown in figure 1.

The logging unit 29 is arranged to be able to receive and store signals from the sensors 21. The signals are led to the logging unit 29 through the leads 23. The logging unit 29 may possibly transmit data to a vessel on the surface (not shown) by means of for example a cable (not shown) . Alternatively the data may be stored in the logging unit 29 and be brought out at a later time when the logging unit is brought up to for example a vessel (not shown) .

The logging unit 29 is brought to and from the well 1 for example by means of a lifting tool (not shown) . The logging unit 29 has a size and a weight making handling by a small vessel possible.

Figure 4 shows a step in the process of preparing the well 1 to be abandoned permanently. A cementing pipe 9c' is connected to the upper section 9a of the well pipe 9 in a way which corresponds to the connecting pipe 9c or the logging unit 29 discussed above. Following removal of the inside barrier 27 in the well pipe 9, a sealing substance 19 is circulated into the lower portion of the well 1 by means of the lower circulation valve 17. The objective of the sealing substance 19 is to provide a first permanent barrier. The seal- ing substance 19 may be of any suitable material, which after placement is transformed from fluid state to solid state. So- called "cement" is an example of such a suitable medium.

At the same time as the sealing substance 19 is circulated inn the well 1, fluid present in the well 1 is displaced by the -sealing substance 19. To achieve a controlled displacement of fluid present in the well 1, the upper barrier 11 is provided with an evacuation valve 31 arranged to be controlled between open and closed positions. The evacuation valve 31 is for example, but not limited to, electrically or hydraulically controlled. The valve control system is of a type known per se and is therefore not shown in the drawings. A person with knowledge in the art will appreciate that the valve needs to be controlled between closed and open positions, and that a check valve is not suitable for this pur- pose.

Figure 5 shows the well following the provision of two more barriers that are provided by means of sealing substance being led into portions of the well 1. The barriers are placed in portions both inside in the lower well pipe section 9b and in the A-annulus between the lower well pipe section 9b and the casing 3.

Cementing pipe 9c' shown in figure 4 and the upper well pipe section 9a are pulled out of the well 1 by in the least that the second coupling device 92 (see fig. 4) and the third coupling device 93 are disconnected from each other.

The upper well pipe section 9a is pulled out of the well to be able to make room for a cutting or hole making tool (not shown) which is arranged to be able to provide openings 34 in one or more of the casings 3 so that sealing substance may be squeezed into a portion of the annulus 33 defined between two casings 3. This is shown accomplished in figure 6, where the well is to be regarded as permanently abandoned. The annulus 33 between the two innermost casings 3 is known as the B- annulus .

The third coupling device 93 placed in an upper end portion of the lower well pipe section 9b is in figure 6 shown protected by a cap 95. Preferably, the cap 95 is placed over the coupling device 93 before the operation of making holes in the casing 3 is carried out and is preferably not removed before sealing substance 19 is filled into a portion of the an- nulus between the casings 3.

In figure 7 the wellhead is removed and the casings 3 are cut below the seabed 5. The casings 3 are cut typically 5-6m below the seabed 5.

Following removal of the cap 95 shown in figure 6, the upper well pipe section 9a is again, in figure 7, connected to the lower well pipe section 9b by means of the coupling devices 92, 93. The cap 95 protects the upper end portion of the upper well pipe 9a.

The well 1 is in figure 7 protected by means of both the settable barriers 11, 13 and the permanent barrier provided by the sealing substance 19.

It is to be noted that in an alternative embodiment (not shown) , sealing substance 19 such as cement is also supplied to the annulus defined between the upper well pipe section 9a and the casing 3 after the upper well pipe section 9a is con- nected to the lower well pipe section 9b. In this alternative solution, the upper well pipe section 9a will be cast fixated to the well 1. It is to be understood that the sealing substance must not be filled higher up than to the lower edge of the first coupling device 91 if this shall be utilised in the future .

While figure 3 shows a logging unit 29 connected to a temporarily abandoned well 1, figure 8 shows the same logging unit 29 connected to a permanently abandoned well 1. Well data may thus be collected from a permanently protected well 1.

In those cases where the well pipe 9, instead of the lead or the signal transmission cable 23, is utilised as communication means to transmit measured results or data from the measuring device (s) 21 in the well to the receiver device 29, the method will be the same as described above.

The present invention thus provides for possibilities to collect information about any development in the well whether it is in operation, is temporarily abandoned or permanently abandoned.

By the very fact that the lower well pipe section 9b is left in the well 1, the operation may be carried out by means of relatively small vessels (not shown) . This will among other things imply reduced cost at the same time as a better permanently protected well is obtained.