Method of monitoring a reservoir

Abstract

A method of monitoring a reservoir comprising setting at least one barrier in a well separating it into upper and lower isolated sections. A perforating gun or other perforating device is provided in the lower isolated section, along with a control mechanism, wireless communication device and a pressure sensor. After the barrier is set, the perforating gun is activated in order to create at least one perforation between the well and a surrounding reservoir. The well, or part of it, is suspended or abandoned but the pressure is still monitored and a wireless, preferably acoustic or electromagnetic, data signal is transmitted from the lower isolated section to above the barrier. Data from the suspended/abandoned part of the well may be used to infer characteristics of the reservoir so that it may be exploited more appropriately especially through another well.

Claims

1. A method of monitoring a reservoir comprising: in a well with a cross-section, setting at least one barrier in the well, such that pressure and fluid communication are resisted across the entire cross-section of the well thus separating the well into a lower isolated section below the at least one barrier and an upper section above the at least one barrier; wherein there is provided an apparatus in the lower isolated section, including: a perforating device; a control mechanism to control the perforating device, and comprising a wireless communication device configured to receive a wireless control signal for activating the perforating device; a pressure sensor; sending a wireless control signal to the wireless communication device to activate the perforating device, the wireless control signal transmitted in at least one of the following forms: electromagnetic, acoustic, inductively coupled tubulars and coded pressure pulsing; after the at least one barrier is set, activating the perforating device, in order to create at least one perforation between the well and a surrounding reservoir; during or after the at least one barrier is set, at least one of suspending and abandoning at least a zone adjacent said lower isolated section; after the perforating device has been activated and after said zone has been at least one of suspended and abandoned: (i) monitoring the pressure in the lower isolated section below the at least one barrier using the pressure sensor; and (ii) sending a wireless data signal including pressure data from below the at least one barrier to above the at least one barrier, using at least one of electromagnetic communication, acoustic communication and inductively coupled tubulars.

2. A method as claimed in claim 1, wherein the method includes monitoring for pressure changes caused by actions in a further well.

3. A method as claimed in claim 1, wherein the at least one barrier is set before the wireless control signal is sent to the wireless communication device, such that the wireless control signal is sent from above the at least one barrier to the wireless communication device below the at least one barrier to activate the perforating device.

4. A method as claimed in claim 1, wherein the perforating device is activated less than a week after the at least one barrier has been set.

5. A method as claimed in claim 1, wherein the at least one barrier comprises one of a bridge plug and a plugged packer.

6. A method as claimed in claim 1, wherein the at least one barrier is formed from a central portion and an annular portion and the central portion is one of at, and below, the annular portion.

7. A method as claimed in claim 1, wherein the at least one barrier includes one of a column of cement, and a cement like material, having a height of at least 2 m.

8. A method as claimed in claim 1, wherein the entire well is at least one of suspended and abandoned.

9. A method as claimed in claim 1, wherein the at least one barrier is a first barrier and at least one second barrier is set above the apparatus, such that the at least one second barrier resists pressure and fluid communication across the entire cross-section of the well, thus isolating a section of the well therebelow and wherein, optionally, the perforating device is activated after the at least one second barrier is set.

10. A method as claimed in claim 1, wherein the apparatus includes a container, and the method includes causing fluid movement through an aperture between an inside and an outside of the container.

11. A method as claimed in claim 10, wherein immediately before fluid movement through the aperture, the pressure inside at least a portion of the container is one of at least 500 psi lower, and at least 500 psi higher, than the pressure outside the container.

12. A method as claimed in claim 10, wherein the aperture is a pre-existing aperture in the container, and a wirelessly controlled control device one of allows and resists fluid movement between the inside and the outside of the container via the aperture.

13. A method as claimed in claim 10, wherein the container has a volume of one of at least 5 l, and at least 50 l, optionally at least 100 l.

14. A method as claimed in claim 10, wherein the container is sealed at the surface, and then deployed into the well such that the apparatus moves from the surface into the well with the container sealed.

15. A method as claimed in claim 10, wherein the aperture is between a first portion of a packer element and a second portion of a packer element, and a perforation is created between the reservoir and the well also between the two portions of the packer element(s), and a short interval test is performed.

16. A method as claimed in claim 15, wherein the portions of the packer element are less than 10 m apart.

17. A method as claimed in claim 1, wherein fluids which are lighter than well fluids are circulated in the well to reduce the hydrostatic head in the well, optionally to a pressure lower than the reservoir pressure, and the at least one barrier is set whilst the hydrostatic head in the well is reduced.

18. A method as claimed in claim 1, including using the apparatus to conduct a drawdown test, flow test, build-up test, connectivity tests, an interval injectivity test and a pressure test.

19. A method as claimed in claim 1, wherein one of (i) an array of discrete temperature sensors, and (ii) a distributed temperature sensor, is provided below the at least one barrier.

20. A method as claimed in claim 1, wherein at least one of the wireless data signal and wireless control signal is transmitted in at least one of electromagnetic signals and acoustic signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagrammatic sectional view of a first embodiment of a well and a well apparatus which may be used in a method of the present invention using acoustic signals;

(3) FIG. 2 is a diagrammatic sectional view of a second embodiment of a well and a well apparatus which may be used in accordance with a method of the present invention using electromagnetic signals;

(4) FIG. 3 is a diagrammatic sectional view of a third embodiment of a well and a well apparatus used for a short interval test in accordance with a method of the present invention; and

(5) FIG. 4 is a schematic view of a container with a floating piston used in certain embodiments.

DETAILED DESCRIPTION

(6) FIG. 1 shows well apparatus 10 comprising an abandoned well 14, liner 12a and casing string 12b. Inside each of the liner 12a and casing string 12b there is an annulus 90A & 90C respectively and, between bridge plugs 22a & 22b, an annulus 90B. The well apparatus 10 further includes a liner hanger 29. The liner hanger 29 is part of a liner hanger assembly from which the liner 12a can be hung.

(7) A string is provided in the well 14 and is divided into a lower tubular 16a, intermediate tubular 16b, and an upper tubular 16c. Bridge plugs 22a and 22b form barriers each across the entire cross-section of the well, and are set in liner 12a and casing string 12b respectively, expanding across the well 14 and splitting the well 14 into three sections. The upper 16c, intermediate 16b and lower tubulars 16a, provide a continuous physical connection in the well to facilitate acoustic communication. Whilst a variety of different options are feasible, the intermediate tubular 16b is more likely “stung in” or attached to the barrier 22a; whilst the tubulars 16a and 16b may be continuous and the barrier/bridge plug 22b formed from a packer element and a central plug.

(8) Two instrument carriers 40 and 46 are provided on the upper tubular 16c. The instrument carriers 40 and 46 each comprise an acoustic relay 44, 49 respectively. A further instrument carrier 30 is provided on the intermediate tubular 16b between the bridge plugs 22a, 22b, and comprises pressure sensor 32 coupled to acoustic relay 31. The relays 44, 49 comprise transceivers which can receive control signals from the surface 11 and send it below the bridge plug 22a to a wireless transceiver (not shown) of an apparatus 50, optionally via the acoustic relay 31. Similarly the relays 44, 49 can receive data from below the bridge plugs 22a and 22b, and send it onwards, such as towards the surface of the well 11.

(9) The surface of the well 11 comprises a cap 13 which covers the well 14. The cap 13 comprises a transceiver 17 coupled to a cable 15. The transceiver 17 is capable of converting the wired signals into acoustic signals for sending down the well 14 to acoustic relays 31, 44 & 49 or vice versa.

(10) This embodiment of the well 14 comprises multiple sections. The first, upper section comprises the upper tubular 16c, the instrument carriers 40 & 46, and bridge plug 22b. The second, middle section comprises the intermediate tubular 16b, instrument carrier 30 and liner hanger 29. The third, lower section comprises the lower tubular 16a, lower bridge plug 22a, and the apparatus 50.

(11) The apparatus 50 is located at the bottom of the lower tubular 16a, and comprises a monitoring mechanism 51 having a pressure sensor (not shown), a control mechanism comprising a gun controller 52 and a wireless transceiver (not shown), and a battery 63. The apparatus 50 also comprises a perforating gun 54 surrounded with an outer housing 60, and a hollow container 57 extending, co-linear, from the perforating gun 54.

(12) The components of the control mechanism (the wireless transceiver and the gun controller 52) are normally provided adjacent each other, or close together; but may be spaced apart.

(13) In use, before running the apparatus 50 into the well 14, the inside of the perforating gun 54 and the hollow container 57 are provided in pressure communication with each other, and sealed at atmospheric pressure at the surface, such that when the apparatus 50 is lowered into position in the well 14, they have a reduced pressure, i.e. they are underbalanced, with respect to the well 14. Shaped charges are provided within the perforating gun 54. In the first instance, the housing 60 of the perforating gun 54 is intact.

(14) The apparatus 50 is run into the well 14 and the barrier set thereabove.

(15) The perforating gun 54 is controlled by the gun controller 52. The wireless transceiver of the control mechanism is configured to receive an acoustic control signal from transceiver 17 of the cap 13, optionally via relays 31, 44 & 49. An operator sends a control signal to activate the perforating gun 54, via the cable 15 to the transceiver 17, where it is then sent acoustically down the well 14 to the wireless transceiver in the control mechanism.

(16) The gun controller 52 then activates the perforating gun 54 in response to the control signal which causes the shaped charges to detonate and pierce through the liner 12a, thus creating perforations 56 in the liner 12a. In use, the detonation of the shaped charges creates apertures 55 in the housing 60 of the perforating gun 54. These apertures 55 allow fluid communication between the inside of the perforating gun 54/attached container 57, and an outside thereof. Thus in this embodiment, there is an underbalance of pressure between the inside of the perforating gun 54/container 57, and a surrounding portion of the well 14. The creation of apertures 55 causes a surge of fluid into the perforating gun 54/container 57 due the underbalance of pressure, thus clearing any debris in or around the apparatus 50 especially the perforations 56. (Debris' here and elsewhere can include perforating debris, filter cake, kill fluid, drilling mud and lost circulation material.)

(17) The monitoring mechanism 51 including the pressure sensor monitors the well 14 which can be used to assess the nature of the reservoir. Moreover, activity on neighbouring wells can be monitored from the FIG. 1 well which can also be used to infer characteristics of the reservoir so that, for example, it may be exploited more appropriately.

(18) Data from the monitoring mechanism 51 can be sent acoustically either continuously, or optionally periodically, to the top of the well 11, and then to the operator via wired cable 15 or alternatively, for a subsea well, via an underwater acoustic modem.

(19) Thus in contrast to the known use of perforating guns in order to create flowpaths for production, in the present embodiment they are used during or after suspending or abandoning a well, below a barrier, in order to provide such monitoring functionality.

(20) It is an advantage of embodiments of the present invention that clearing the debris in the perforations or surrounding formation allows data more representative of reservoir conditions to be gathered and sent to the surface.

(21) In alternative embodiments, the perforating gun may be activated during the abandonment operation, that is, after setting a first barrier and prior to setting a second barrier.

(22) The container 57 provides more volume to create a stronger “surge” effect. However alternative embodiments of the invention do not require a container and can rely on the underbalance effect using the inside of a perforating device. In an alternative modification to the FIG. 1 embodiment, the container may be removed, shortened or extended by removing or adding further lengths of tubing in order to create a smaller or larger drop in pressure when the shaped charges are fired.

(23) For certain embodiments, the container may have a further aperture independent of the perforating gun which may be sealed by a valve for example, and such a valve controllable to open up to create a secondary surge from the container at a later time than the initial surge created by the inside of the perforating gun.

(24) Alternative embodiments comprise only the lower tubular and the intermediate tubular and not the upper tubular, that is there is no tubular above the bridge plug 22b. In such embodiments, one option is to attach relays to the inside or outside of the casing string.

(25) FIG. 2 shows an embodiment of an apparatus 150 where activation of an underbalanced container is independent of perforating guns. Like parts with the FIG. 1 embodiment are not described in detail but are prefixed with a ‘1’. FIG. 2 shows an abandoned well 114 comprising packer 122a, two bridge plugs 122b, 122c, a cement seal 120 and a cap 113 at the top of the well 111. Compared to FIG. 1, FIG. 2 relies on electromagnetic communication and so comprises only a lower tubular 116a. Packer 122a seals the annulus at the top of the lower tubular 116a, and bridge plug 122c seals the bore near the top of the lower tubular 116a. Bridge plug 122b seals across the entire cross-section of the well, as do the combination of bridge plug 122c and packer 122a. Between bridge plugs 122b and 122c, and immediately below bridge plug 122b, there is provided an EM instrument carrier 121 comprising a transceiver 123.

(26) A communications device 119 provides a contact spaced from the suspended or abandoned well 114 in order to transmit and receive electromagnetic signals. The communications device 119 is also capable of storing data for retrieval at a later date.

(27) Similar to the FIG. 1 embodiment, the apparatus 150 comprises a perforating gun 154, a battery 163, a monitoring mechanism 151 with a pressure sensor (not shown). It also comprises control mechanisms, albeit for the valve as well as a separate control mechanism for the perforating gun, each control mechanism comprising a wireless transceiver (not shown) and a valve controller 166 and gun controller 152 respectively.

(28) Shaped charges are provided within the perforating gun 154, and when activated create apertures 158.

(29) However in contrast to FIG. 1, a container 159 is spaced below the perforating gun 154, at the end of the lower tubular 116a. The container 159 has an aperture 155, and a valve 162 controlling the aperture 155. Compared to FIG. 1, a second control mechanism comprising the valve controller 166 is provided to control the valve 162, along with a further wireless receiver (or transceiver) (not shown). The container 159 can have a volume capacity of, for example, 1000 litres.

(30) Independent of the operation of the perforating gun 154, the valve 162 is configured to obstruct and isolate the aperture 155 to seal the container 159 from the surrounding portion of the well 114 in a closed position and allow pressure and fluid communication between a portion of the container 159 and the surrounding portion of the well 114 via the aperture 155 in an open position. In use, the valve 162 is moved from the closed position to the open position in response to a wireless control signal.

(31) In some embodiments, the container 159 is filled with a gas, such as air, initially at atmospheric pressure. In such embodiments, the gas is sealed in the container 159 at the surface before being run into the well 114. This helps to create an underbalance of pressure, for example 1,000 psi to 10,000 psi, between the container 159 and the surrounding portion of the well 114 (which is at a higher pressure than atmospheric pressure on the surface).

(32) After the perforating gun 154 has fired, as described above with respect to FIG. 1, the container 159 can be used to create a pressure surge into the container 159 to clear the debris in and around the perforations/formation before monitoring the well 114, or the adjacent reservoir.

(33) In use, the valve 162 is initially in the closed position. An electromagnetic signal is sent to wireless transceiver (not shown) from an operator, optionally via transceiver 123. The gun controller 152 then activates the perforating gun 154 in response to the control signal such that the shaped charges are detonated and pierce through the housing 160 of the perforating gun 154, and also through the liner 112a, thus creating perforations 156 in the liner 112a. An electromagnetic signal is then sent, optionally at an earlier or much later time, to the further transceiver instructing the valve controller 166 to open the valve 162 controlling an aperture 155. The underbalance of pressure in the container 159 causes a surge of fluid into the container 159 via the aperture 155.

(34) Once the well 114 is more clear of debris, the monitoring mechanism 151 can then more effectively monitor the reservoir, or optionally monitor the effect on the reservoir of activity on other wells linked to the reservoir and can communicate the data electromagnetically to the top of the well 111. The cable 115 and communication box 119 form a spaced contact to detect and transmit electromagnetic signals, and the communication box 119 is used as an interface to a local or remote data acquisition and control system.

(35) In some embodiments, the container may be overbalanced, or have an overbalance portion, that is an area of increased pressure compared to a surrounding portion of the well. In such embodiments, once a valve is opened, there is a surge of fluid from the container into the surrounding portion of the well. The apparatus is particularly suited in this case to deploying acid for an acid treatment. The container may be filled with hydrochloric acid or other acids or chemicals used for such so-called acid treatments. Acid wash normally treats the face of the wellbore, or may treat scale within a wellbore, or it may be performed to try to mitigate perforation debris or other skin damage. Acids may be directed towards specific areas, for example by using openings in a tube. The aperture may comprise a tube extending along the wellbore with a plurality of openings. The acid treatment may then pass along the tube and exit into the well at the appropriate location. The overbalanced container may be used instead of an underbalanced container. Alternatively a pressure balanced container comprising a pump may be used to deploy the acid treatment instead of an overbalanced container. Additionally a discrete temperature array (not shown) may be used across the perforation gun to monitor the acid treatment and reservoir.

(36) In some embodiments, the valve can also be opened before activating the perforating device. Optionally, the same container is used to clear the well of debris both before and after activating the perforating devices, but in some embodiments there may be more than one container, or more than one chamber within a container. For example, one container/chamber may be used to clear the well before the perforating device is activated, and the second used after.

(37) For certain embodiments, the valve may be opened immediately after the perforating guns have activated. In other embodiments, the opening of the valve may be delayed for some time after the perforating gun has fired. Likewise, the activation of the perforating guns may be delayed after the barrier is set. It may, for example, be activated immediately prior to testing an adjacent well. The activation of the perforating guns could also occur after the rig connected to the well has been removed.

(38) In some alternative embodiments, one or a first group of shaped charges provided in the perforating gun may be detonated before a second or second group of shaped charges. Further embodiments may have multiple perforating guns, where each perforating gun may be separated by a barrier, such as a bridge plug or a packer.

(39) FIG. 3 shows a further embodiment of the apparatus 250. Like parts with the FIG. 2 embodiment are not described in detail but are prefixed with a ‘2’. FIG. 3 shows an abandoned well 214 comprising two bridge plugs 222a & 222b, and two packer elements 270a & 270b between a lower tubular 216a and a liner 212a. The two packer elements 270a, 270b are spaced apart along the well 214 and define a short interval. Like the embodiment described in FIG. 2, FIG. 3 relies on electromagnetic communication.

(40) The apparatus 250 in FIG. 3 comprises a valve 262, a choke 276, an aperture 255, a control mechanism with a wireless receiver or transceiver (not shown) and multi-purpose controller 266; a battery 263, a monitoring mechanism 265 with a pressure sensor, and a container 259 which can have a volume capacity of, for example, 100 litres. There is an underbalance of pressure between the container 259 and a surrounding portion of a well 214 within the short interval between packer elements 270a and 270b.

(41) The battery 263 powers the components of the apparatus 250, for example the multi-purpose controller 266, the monitoring mechanism 265 and the transceiver. Often a separate battery is provided for each powered component. In alternative embodiments, downhole power generation may be used, for example, by thermoelectric generation.

(42) The choke 276 is located adjacent to the valve 262, optionally spaced apart from the valve, in a passageway 261 between the aperture 255 and the container 259. The rate at which fluid enters the container 259 is controlled by the cross-sectional area of the choke 276. In alternative embodiments, the choke 276 and valve 262 positions can be in the opposite order to that illustrated, or they may be combined into a single component.

(43) Compared to the FIG. 1 and FIG. 2 embodiments, the FIG. 3 embodiment comprises a punch gun 254 with a single aperture 258 which in use, creates a single perforation 256 in the liner 212a. In contrast to FIG. 2, the punch gun 254 and the valve 262 of FIG. 3 are both controllable by the same multi-purpose controller 266 and the same wireless transceiver.

(44) The aperture 255 of the container 259 is located within the short interval between the packer elements 270a and 270b. The punch gun 254 is also located within the short interval, such that in use the punch gun 254 activates and creates the single perforation 256 within the short interval to allow fluid communication between the reservoir (not shown) and the surrounding portion of the well 214 within the short interval.

(45) The well may be manipulated by conducting a flow test, whereby flow from the reservoir is produced into said defined short interval, and proceeds through the apparatus. In use, the packer elements 270a and 270b are initially set in the liner 212a to define the short interval for testing. The multi-purpose controller 266 then receives an electromagnetic control signal to activate the punch gun 254 which creates perforation 256 in the liner 212a and adjacent formation (not shown) to allow fluid communication between the formation and the surrounding portion of the well 214 in the short interval.

(46) The multi-purpose controller 266 then receives a further electromagnetic control signal to open the valve 262. The container 259, which is underbalanced, can then receive flow in a controlled manner from the perforated interval between the two packer elements 270a and 270b.

(47) The debris in or around the perforation 256 is also drawn into the container 259 due to this underbalance of pressure, thus helping to clear the surrounding portion of the well 214 in the short interval. The underbalance effect is concentrated in the short interval thus extends the radius of the reservoir upon which it acts. This can help to improve well flow and allow more accurate data to be obtained from the flow test.

(48) Pressure is monitored by the monitoring mechanism 265 both before the valve 262 is opened and as the flow enters the container 259 at a rate controlled by the choke 276.

(49) The valve 262 is closed before significant pressure builds up in the container 259. A relatively limited flow test can thus be conducted in the short interval between the packer elements 270a and 270b. Data from the monitoring mechanism 265 or other sensors in communication with the short interval, such as between the two packer elements 270a, 270b or below the lower packer element 270a in the passageway 261 adjacent to the choke 276, can provide useful flow test information. The response of the reservoir to the flow test and build-up can elicit useful information on the reservoir characteristics.

(50) It is an advantage of certain embodiments of the present invention that the short interval flow tests may be conducted with barrier(s), such as bridge plugs and packers, in place as this may help to increase the safety of the well. The barrier(s) may also allow the short interval tests to be carried out concurrently with other well activities and operations which are occurring above the barrier(s). This can save rig time.

(51) In some embodiments, after the liner has been perforated the well may be monitored for a short period of time, for example the well may flow at a low rate for up to 24 hours into the container. In some embodiments, the well may be monitored whilst the well above the barrier is being abandoned.

(52) A variety of alternatives are available for such a flow test of a short interval. Two or more such flow tests can be conducted. In one embodiment, the valve 262 can be opened again and further fluid can enter the container 259. This open/close sequence can be repeated until the container 259 is full. Alternatively or additionally, further underbalanced containers may be provided to conduct the further flow test(s).

(53) As a further option, a second underbalanced container is provided which can be used to purge the short interval, before the apparatus 250 is used to conduct the flow test on the short interval, as described above.

(54) In some embodiments, the container 259 or additional containers may have an overbalance of pressure compared to the surrounding portion of the well 214 in the short interval. In such embodiments, the apparatus may be used to conduct an interval injectivity, permeability, well/reservoir treatment, hydraulic fracturing, minfrac or similar test/procedure which may require pressure to be applied between two annular sealing devices, such as between the packer elements 270a and 270b defining a short interval. A similar effect can be achieved by a pump instead of a pressurised container. In any case, the effect is concentrated in the short interval and thus penetrates the formation more.

(55) In alternative embodiments, a short gun may be used instead of a punch gun.

(56) A particularly suitable apparatus for FIG. 3 applications is shown in FIG. 4. The FIG. 4 apparatus comprises an aperture 355, a valve 362, a choke 376 and a control mechanism with a multi-purpose controller 366 and a wireless receiver (or transceiver) (not shown); and a container 357. The valve 362 and the choke 376 are located in a central portion of the apparatus in an aperture 379 between two sections of the container 357—a fluid chamber 371 and a dump chamber 381.

(57) A floating piston 375 is located in the fluid chamber 371. The fluid chamber 371 is initially filled with oil below the floating piston 375 through a fill aperture (not shown). When the floating piston 375 is located at the top of the fluid chamber 371 it isolates/closes the fluid chamber 371 from the surrounding portion of the well, and when the floating piston 375 moves towards the bottom of the fluid chamber 371 the opening 355 allows fluid to enter the fluid chamber 371 via flow aperture 359 from outside of the container, normally the surrounding portion of the well. The location of the floating piston 375 is controlled indirectly by the flow of fluid through the valve 362, which is in turn controlled via signals sent to the multi-purpose controller 366.

(58) In use, the sequence begins with the valve 362 in the closed position and the floating piston 375 located towards the top of the fluid chamber 371. Fluid in the well is resisted from entering the fluid chamber 371 via the aperture 355 by the floating piston 375 and oil therebelow whilst the valve 362 is in the closed position. A signal is then sent to the multi-purpose controller 366 instructing the valve 362 to open. Once the valve 362 opens, oil from the fluid chamber 371 is directed into the dump chamber 381 by the well pressure acting on the floating piston 375, and fluids from the surrounding portion of the well are drawn into the fluid chamber 371. The rate at which the oil in the fluid chamber 371 is expelled into the dump chamber 381, and consequentially the rate at which the fluids from the well can be drawn into the container 357, is controlled by the cross-sectional area of the choke 376.

(59) Alternatively, a pump may be used instead of the underbalanced pressure in the container in order to draw fluids into the container.

(60) It is an advantage of the FIG. 4 embodiment that the floating piston and choke can help to control the rate of flow of well fluids and debris from the surrounding portion of the well into the container, which may allow more accurate data to be obtained and therefore better analysis of the well and reservoir can be carried out.

(61) Modifications and improvements can be incorporated without departing from the scope of the invention. For example, the features of FIG. 1 and FIG. 2 may be combined such that the apparatus may comprise more than one underbalanced container, and the control signals may be transmitted acoustically and/or electromagnetically. Similarly, the FIG. 3 embodiment may rely on acoustic communication instead of or in addition to electromagnetic communication.

(62) Moreover, the figures show the well in a suspended state. Before the stage shown in the figures a rig may be connected to the well which is not covered by a cap. A first barrier could be set and then a perforating device activated whilst the rig is still present and before a second barrier is set. After these steps, the second barrier would be set, and subsequently the connection with the rig removed and a cap put in place.