WO1992006271A1

WO1992006271A1 - Apparatus for releasing fluid into a well

Info

Publication number: WO1992006271A1
Application number: PCT/GB1991/001676
Authority: WO
Inventors: Neil Andrew Abercrombie Simpson; Raymond Paul Coey
Original assignee: Astec Developments Limited
Priority date: 1990-09-29
Filing date: 1991-09-27
Publication date: 1992-04-16
Also published as: AU8541291A

Abstract

There is described apparatus for releasing working fluid into a well to simulate 'kicks'. The apparatus includes a housing which defines a chamber (13) containing working fluid which is to be selectively released into the well (16) to simulate the 'kick'. The working fluid is pressurised by well fluid as the apparatus is lowered into the well.

Description

"Apparatus for Releasing Fluid into a Well"

The invention relates to apparatus for releasing fluid into a well and in particular, apparatus for simulating a situation known as "kick" during the drilling of wells.

The drilling of oil and gas wells, both onshore and offshore, involves major dangers and one of the biggest of these dangers is the risk of the formation fluids reaching the surface in an uncontrolled manner. This situation is commonly known as a "blowout" and can result in major damage to or loss of the drilling equipment, and worse, the risk to and possible loss of human lives.

A "kick" is the first absolute sign of an impending blowout. A kick is when formation fluid (gas and/or liquid) enters the well bore under pressure and is sufficient to cause the well to "flow", that is mud from the well is pushed out of the annulus and/or drill pipe at the surface. Extensive effort is being put into the safety systems on modern drilling rigs to provide early warning of blowout situations and to provide the necessary equipment to handle these situations safely. However, if blowouts are to be prevented, it is essential that the personnel required to handle these situations are well trained and have regular pressure control drill practice in order to identify a kick as early as possible and control it before it can become a blowout.

Conventionally, the bulk of the training which is given is conducted in a classroom environment in which the theory is well covered on a one-to-one basis. Practice is also provided by using computer simulations or a specialised training well with the facility to introduce influx fluid at the bottom of the casing by means of pipes run down the outside of the casing. However, with the exception of the latter case, these systems are unable to reproduce completely and effectively the experience of a natural "kick" in a well. Specialised training wells are expensive to produce and run and are consequently few in number. They are also at fixed locations.

In accordance with one aspect of the present invention, there is provided apparatus for releasing working fluid into a well, the apparatus comprising a housing for insertion into the well, the housing having a chamber for containing the working fluid to be released, release means associated with said working fluid chamber to permit exit of the working fluid from the chamber into the well, and means for communicating the working fluid chamber, when the housing is lowered into a well, with a well fluid within the well such that said well fluid exerts a pressure on working fluid within the chamber. The invention mitigates the problem of prior art devices by enabling training to be carried out on location and by providing a more realistic simulation of a "kick". The invention also provides a functional test for all the equipment and personnel before drilling out into an open hole situation.

Preferably, the housing also comprises an inlet valve to enable the working fluid to be inserted into the chamber.

Preferably, the means for communicating the working fluid chamber with the well fluid is constituted by the chamber being open at its lower end to communicate with the through bore in the drill string.

Preferably, the working fluid has a density less than the density of the well fluid.

The release means may be in the form of a threshold valve which opens when a predetermined pressure differential exists between the working fluid and the pressure in the well. Alternatively, the release means may be in the form of a pressure regulator device.

The apparatus may be connected to a drill string so that the apparatus is lowered into the well with the drill string. In such cases, where the apparatus forms part of the drill string, the end of the chamber opposite to the open end of the chamber is sealed by means of a valve and the apparatus further includes a well fluid chamber adjacent to and above the working fluid chamber separated from the working fluid chamber by said valve. The valve permits well fluid to pass from the well fluid chamber into the working fluid chamber but prevents working fluid from passing from the working fluid chamber into the other chamber. The valve may be a flap valve.

Preferably, the well fluid chamber communicates with the central bore in the drill string which is connected to the apparatus above the apparatus and an aperture in the housing provides fluid communication between the well and the well fluid chamber.

Preferably, the open end of the working fluid chamber communicates with the central bore in the drill string below the apparatus so that well fluid within the drill string below the apparatus may act to pressurise the working fluid in the working fluid chamber as the drill string and the apparatus are lowered into the well.

Preferably, the apparatus also comprises sealing means which seals the valve after the working fluid has exited from the working fluid chamber into the well and the sealing means may also seal the aperture between the well and the well fluid chamber after the working fluid has exited from the working fluid chamber into the well.

In addition, a non-return valve may be positioned in the drill string below the apparatus so that the working fluid is prevented from exiting through the bottom of the drill string. This enables more working fluid to be inserted into the working fluid chamber without the working fluid escaping through the bottom of the drill string. Preferably, the non-return valve is located adjacent a drill bit at the lower end of the drill string below the apparatus.

The non-return valve comprises a valve seat having a through aperture and a valve member which is free inside the drill string and co-operates with the upper surface of the valve seat to seal the through aperture to enable the section of drill string above the valve seat to be pressurised above the normal pressure that can be obtained without the non-return valve. In this case the valve member floats on the top of the well fluid but sinks to the bottom of the working fluid.

Preferably, the valve member is spherical.

The advantage of the non-return valve is that it permits more significant "kicks" in shallow wells than would otherwise be possible, due to the lower volume and pressure in shallow wells. This is because higher pressures of working fluid may be used to enhance the size of the kick.

The working fluid may be gaseous and is preferably an inert gas, such as nitrogen. The well fluid is a drilling mud. However, the working fluid could be a liquid or a liquid/gaseous mixture.

An example of apparatus for releasing a working fluid into a well in accordance with the invention will now be described with reference to the accompanying drawings, in which:-

Fig.l is a schematic diagram of apparatus for releasing fluid into a well; Fig.2 is a schematic diagram showing the apparatus of Fig.l in use; Fig.3 is a schematic cross-sectional view through an outlet port in the apparatus shown in Fig.l; Figs.4a, 4b, 5a and 5b are graphs showing the pressure change in the apparatus and well as a function of well depth; Fig.6 is a schematic diagram similar to Fig.2 showing use of the apparatus of Fig.l in a relatively shallow well; Fig.7 is a cross-sectional view through the apparatus shown in Fig.l showing in detail a non-return valve for use in the apparatus; Figs.8a, 8b and 9 illustrate a modified version of the apparatus.

Fig.l shows a downhole tool 11 which comprises a valve sub body 1 which has a through bore 12 with a threaded pin connection 10 at its lower end and a threaded box connection 9 at its upper end. The pin connection 10 and the box connection 9 enable the tool 11 to be connected into a drill string and the through bore 12 communicates with the corresponding through bore in the drill string to which the tool 11 is connected. Within the through bore 12 there is provided a working fluid chamber 13 and a well fluid chamber 14 which are separated by a valve 4. The well fluid is typically drilling mud. The valve 4 enables mud to pass from the well fluid chamber 14 in to the working fluid chamber 13 but prevents working fluid from passing from the working fluid chamber 13 into the well fluid chamber 14. The valve 4 is in the form of a flap valve which is fixed to the sub body 1 by a pivot 20. This enables the valve 4 to pivot downwards from the position shown in Fig.l.

The valve 4 is shown in more detail in Fig.7 where it can be seen that the valve 4 comprises a cylinder 82 defining a valve seat 80, and a valve flap 81. The valve flap 81 is cut from a tube whose internal diameter corresponds to the maximum outer diameter of the valve seat 80 such that the seat 80 and flap 81 have mating seating faces. The seat 80 is machined as a contour on the end of the cylinder 82.

As shown in Fig.7, the cylinder 82 is located within a tube 83 lining the inside of the sub body 1 and the flap 81 is attached to the tube 83 by means of a pivot pin 84 which corresponds to the pivot 20 of Fig.l and which permits the flap 81 to pivot through 90° between sealing engagement with the seat 80 and a fully open position shown in phantom in Fig.7. The tube 83 has the same internal diameter as the tube from which the flap 81 is cut and a corresponding aperture 85 which replicates the shape of the flap is cut from the tube 83 so that the flap 81 when fully open sits within the aperture 85 and does not obstruct the flow of fluid through the tool 11.

The advantage of this valve arrangement is that the valve 4 can fit into any reasonably sized pipe without over-restricting the bore of the pipe and hence fluid flow within the bore. Such an arrangement could be used in small diameter bores.

In addition to use in the tool 11, the valve arrangement shown in Fig.7 may be used in other applications where there is a limited amount of space available, for example sub-sea safety valves, coring applications and blow-out preventors.

An inlet port 7 connects the working fluid chamber 13 with the outside of the tool 11 and permits the introduction of a working fluid into the working fluid chamber 13. Release means in the form of an outlet port 5 enables fluid within the working fluid chamber 13 to exit from the chamber 13. The outlet port 5 includes a threshold valve 28 (see Fig.3) comprising an insert 24 held within the outlet port 5 by an O-ring seal 23. The insert 24 has a through bore 25, a rupture disc 26 adjacent to the end of the insert 24 nearest the chamber 13 and a plug 27 at the outer end of the insert 24. There may be fluid between the disc 26 and the plug 27 which typically would have a pressure of 1 atmosphere when the tool 11 is on the surface. Alternatively, there may be a vacuum between the disc 26 and the plug 27.

A flood port 3 is also provided in the valve sub-body 1 and connects the well fluid chamber 14 with the outside of the tool 11. Also provided within the valve sub body 1 is a sealing sleeve 2 and a set of upper top and bottom seals 8 and a set of lower top and bottom seals 6. The sealing sleeve 2 is movable within the through bore 12 of the tool 11 to open the ports 3,5 or to close and seal the ports 3,5 to prevent the ports 3,5 communicating between chambers 14,13 respectively and the outside of the tool.

Although only one outlet port 5 and one flooding port 3 are shown there may be more than one outlet port 5 and/or flooding port 3.

As shown in Fig.2 a 13 3/₈" casing 19 has been set and cemented to approximately 6,000 feet below the sea bed 29 in a well 16. At this stage, acceptable pressure tests have been conducted on the well and the well is now ready to drill out through the casing 19 and into open hole. Typically, the down hole tool 11 is connected to the upper end of a lower drill string 17 at about two thousand feet from a drill bit 15. Before the tool 11 is lowered into the well 16 a working fluid, such as water, or a gas, such as nitrogen, is introduced into the working fluid chamber 13 through the inlet port 7 until the desired volume of working fluid is within the working fluid chamber 13 extends into the lower section of the drill string 17. As the working fluid is inserted into the working fluid chamber 13 the equivalent mud volume is displaced from the lower end of the drill string 17 via the annulus 30 between the drill string and the casing 19. The volume of mud returned can be used as a second recheck on the calculated volume of the working fluid which has been inserted into the working fluid chamber 13 through the inlet port 7. After the required volume of the working fluid has been inserted into the working fluid chamber 13 the tool 11 is lowered into the hole as further sections of drill string 18 are added above the tool 11 and connected to the box connection 9.

During this stage the drilling mud within the well floods the drill string 18 above the tool 11 by entering through the flood port 3 and the mud chamber 14 above the non-return valve 4. The working fluid within the chamber 13 is subjected to increasing hydrostatic pressure as it is run deeper into the well 16. If the working fluid is a liquid, such as water, then the volume will remain substantially unchanged as it can be considered as an incompressible fluid. However, if the working fluid is a gas, such as nitrogen, the volume of the fluid will decrease as the pressure increases, in accordance with Boyle's Law, that is:- ^±^ = ^P ₂ ^V ₂' ^wnere ?ι ^and ^ are the initial pressure and volume, respectively and P₂ and V₂ are the final pressure and volume, respectively.

Figs.4a and 4b illustrate graphically the change in pressure in the annulus 30 and within the drill string 17,18 as a function of the depth of the well 16, with water as the working fluid. Taking the pressure gradient of drilling mud as 0.624 psi/ft and the pressure gradient of water as 0.410 psi/ft, the pressure of mud at the bottom of the well 16, that is at 6000 feet, is 3744 psi. The pressure of mud in the annulus 30 at 4000 feet, that is adjacent the position of the tool 11 in the drill string, is 2496 psi. With the example shown in Figs.4a and 4b a column of 500 feet of water 50 is inserted into the working fluid chamber 13 and drill string 17 at the surface (see Fig. 4a) and as water can be considered as incompressible it will still be a column of 500 feet when the top of the column is at 4000 feet (see Fig. 4b)in the well. The pressure at the bottom of the water column at 4500 feet, that is at the mud/water interface in the drill string, is given by the pressure at the drill bit (or 6000 feet) minus the pressure difference over a column of mud with a height of 1500 feet, that is 3744 psi - (1500 x 0.624) = 2808 psi. The pressure at the top of the water column, that is at the position of the tool 11 is then 2808 psi minus the pressure difference over a 500 ft column of water, that is 2808 - (500 x 0.416) = 2600 psi. Hence, there is a pressure difference between the chamber 13 in the tool 11 and the annulus 30 outside the tool at 4000 feet of 2600 - 2496 = 104 psi as shown by the plateau 51 on the graph in Fig.4b.

A similar type of situation exists when a gas, such as nitrogen, is used as the working fluid and Figs. 5a and 5b show a similar situation with a typical gas as the working fluid. In this case the calculations are more complicated as the volume of a gas column 60 changes as the gas column 60 is lowered further into the well because the gas compresses.

In order to obtain a 1525 feet column of gas 60 in Fig.5a it is necessary to have a pressure of 905.8 psi at the inlet 7 when the gas is injected into the tool 11 and the drill string 17 at the surface. A typical gas at a pressure of about 900 psi would have a pressure gradient of about 0.03 psi/ft. When the drill string and tool 11 is lowered down into the well the column of gas 60 compresses until it has a height of 500.8 feet (see Fig.5b) when the tool 11 is at 4000 feet and the bit 15 is at 6000 feet. As the gas has been compressed by about one third, the density of the gas will have increased by a factor of three and hence, the pressure gradient of the gas will have increased to about 0.1 psi/ft. This gives a pressure at the top of the gas column 60 of 2758 psi and a difference in pressure between the chamber 13 and the mud in the annulus 30 at 4000 feet of 2758 psi - 2496 psi = 262 psi, as shown by plateau 61 on the graph in Fig.5b.

The pressure and volume changes shown in Figs.4a, 4b, 5a and 5b have not taken into account the effects of changes in temperature as these can be considered as negligible when compared with the other variables acting on the working fluid.

As the pressure of the fluid within the working fluid chamber 13 rises to a predetermined level the disc 26 in the threshold valve 28 which is mounted in the outlet port 5 bursts and the plug 27 is forced out of the insert 24 when the predetermined pressure level has been reached. This causes release of the working fluid into the annulus 30 between the drill string and the casing 19. Preferably, this occurs at about 4000 feet below the surface that is when the drill bit 15 is at about 6000 feet below the surface 29. When the outlet valve 5 opens the mud adjacent the drill bit 15 enters the drill string 17 through the drill bit 15 and flushes the working fluid out of the working fluid chamber 13 through the outlet port 5 until the working fluid has been completely displaced from within the drill string 17. This will cause the volume of mud in the annulus to drop as it replaces the working fluid by entering the drill string 17 at the bit 15.

With a liquid working fluid, all the working fluid moves from the working fluid chamber 13 into the annulus 30 so that the pressure differential across the non-return valve 4 drops and the hydrostatic pressure in the annulus drops due to the reduction in the volume of the mud in the annulus which is replaced by the working fluid which is less dense. This causes the mud in the well fluid chamber 14 to exert a positive pressure to cause the mud to flow out of the flooding ports 3 into the annulus and this in turn causes the well to start to flow.

In the case of a working fluid which is gaseous, the pressure differential between the well fluid chamber 14 and annulus 30 remains positive for longer and the expanding gas in the annulus causes the well to flow.

When the kick is detected the well can be "closed in" and "killed" as per standard procedures.

However, if the well is "closed in" early then the pressures will build up as normally associated with a kick but as these pressures stabilise, some of the working fluid will remain within the drill string 17. The working fluid remaining within the drill string 17 will only be released if the annulus pressure is allowed to drop below its initial closed in pressure. This means that if the well killing procedure is not carried out properly then there is the potential for a second influx into the annulus between the drill string and the well.

Once the simulated kick has taken place and all the working fluid has circulated out of the well the sealing sleeve 2 is moved down to hold the non-return valve 4 open and to seal off the flooding port 3 and the outlet port 5. The drill string can then function as a normal drill string as drilling mud may circulate from the upper drill string 18 through the chambers 13,14 in the tool 11 to the lower drill string 17 as the non-return valve 4 is now open. Hence, the well can now be drilled out.

The downhole tool 11 may be recovered from the drill string when the drill string is next removed from the well, for example for a bit or assembly change.

The downhole tool 11 is advantageous when used in deeper wells where the operating volumes and pressures allow for more significant "kicks" . In shallow wells the "kick" on surface is reduced as a consequence of the lower volume and pressure.

However, this disadvantage may be overcome if a simple floating ball type of non-return valve 70, 71 is used and the seat 70 of the valve is placed close to the bit 15, as shown in Fig.6 As the system is pressurised the ball 71 floats on the surface 72 of the mud 73 until all the mud is forced out of the drill string 17 leaving the ball 71 sitting on the seat 70. At this stage any further applied pressure is effectively an over-pressure which will enhance the size of the kick. It should be noted that the over-pressure must not exceed the hydrostatic pressure at the bottom of the well. Once the drill string has been run back into the well the hydrostatic pressure due to the mud will eventually lift the ball off its seat and pressurise the gas as per the deeper well system described above.

The downhole tool 11 could also be used for kick simulation downhole for example whilst circulating or pulling out and the size and type of kick can be easily varied. For example by using a liquid as the working fluid, a liquid kick can be simulated, by using a gas, a gas kick can be simulated or if desired a combination of both liquid and gas can be used with the bit either on the bottom of the hole or off the bottom of the hole which entails stripping back into the hole.

The downhole tool 11 is very versatile as a training tool as it utilises conventional drilling equipment and wells and thereby reduces the cost and maximises safety.

In an alternative mode of operation as illustrated in Figs 8a, 8b and 9 the apparatus is modified in such a way that the simulated gas influx is bled in a controlled manner from the captive charge contained within the working fluid chamber.

The working fluid is injected into working fluid chamber as before. The release means is however in the form of a pressure regulator valve. As a further modification the apparatus is latched to the drill string above it, thereby allowing the apparatus containing a volume of pressurised, captive working fluid to be deposited at the bottom of the well.

The operation of the apparatus in such a situation is as follows. The working fluid is introduced into the working fluid chamber through the charging port until a pre-specified internal pressure has been attained. (This pressure will not exceed the hydrostatic pressure at the bit at that time, and known volume of gas for a given mud-weight will be contained in the drill string) .

The drill string containing the apparatus is run into the well in its normal manner until the drill bit bottoms out. The working fluid contained within the working fluid chamber will increase in pressure due to the hydrostatic effects within the well-bore. The well fluid in effect being used as a sliding piston. A latching mechanism located in the drill string a±>ove the apparatus is then activated, preferably remotely from surface, thereby jettisoning the apparatus with the pressurised working fluid at the bottom of the well.

Once the latching mechanism has been activated, the apparatus discharges a discrete portion of the captive working fluid after a pre-determined period of time. This may be achieved by various means. For example, a hydraulically driven piston may be used displacing a volume of oil until the release mechanism is tripped. Alternatively, a toggle switch utilising a change in the well-pressure could be used.

Once activated the pressure regulator will continue to bleed working fluid into the well-bore until the "kick" is detected on surface and steps taken to stop it. This will ultimately involve an increase in the pressure within the well-bore to a point greater than the pre-determined operational setting for the pressure regulator. For instance the pressure regulator could be set for 200 psi, thereby requiring the well-bore pressure to be increased accordingly.

If at any time the well-bore pressure is allowed to decrease such that there is no differential between it and the pressure regulator, then the regulator will operate once again until further steps are taken at surface to stop it. This situation will continue until either; (i) all the working fluid has been bled from the working fluid chamber, or (ϋ) the apparatus is withdrawn from the well.

Once the training exercise has been completed the latching mechanism attached at the bottom end of the upper drill string may then be engaged and the whole assembly returned to surface.

Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims

1. Apparatus for releasing working fluid into a well, the apparatus comprising a housing for insertion into the well, the housing having a chamber for containing the working fluid to be released, release means associated with said working fluid chamber to permit exit of the working fluid from the chamber into the well, and means for communicating the working fluid chamber, when the housing is lowered into a well, with a well fluid within the well such that said well fluid exerts a pressure on working fluid within the chamber.

2. Apparatus as claimed in Claim 1, wherein said means for communicating the working fluid chamber with the well fluid is constituted by the chamber being open at its lower end to communicate with the through bore in the drill string.

3. Apparatus as claimed in either preceding claim, wherein the working fluid has a density less than the density of the well fluid.

4. Apparatus as claimed in any preceding claim, wherein the housing includes an inlet valve to enable the working fluid to be inserted into the chamber.

5. Apparatus as claimed in any preceding claim, wherein said release means is in the form of a threshold valve which opens when a predetermined pressure differential exists between the working fluid and the pressure in the well.

6. Apparatus as claimed in any one of Claims 1 to 4, wherein said release means is constituted by a pressure regulator device.

7. Apparatus as claimed in any preceding claim, wherein the apparatus is connected in a drill string so that the apparatus is lowered into the well with the drill string.

8. Apparatus as claimed in Claim 7, wherein the end of the chamber opposite the open end of the chamber is sealed by means of a valve and the apparatus further includes a well fluid chamber adjacent to and above the working fluid chamber separated from the working fluid chamber by said valve.

9. Apparatus as claimed in Claim 8, wherein said valve permits well fluid to pass from the well fluid chamber into the working fluid chamber but prevents working fluid from passing from the working fluid chamber into the other chamber.

10. Apparatus as claimed in Claim 9, wherein said valve is a flap valve.

11. Apparatus as claimed in any preceding claim, wherein the well fluid chamber communicates with the central bore in the drill string which is connected to the apparatus above the apparatus and an aperture in the housing provides fluid communication between the well and the well fluid chamber.

12. Apparatus as claimed in any preceding claim, wherein the open end of the working fluid chamber communicates with the central bore in the drill string below the apparatus so that well fluid within the drill string below the apparatus may act to pressurise the working fluid in the working fluid chamber as the drill string and the apparatus are lowered into the well.

13. Apparatus as claimed in any preceding claim, wherein the apparatus includes sealing means which seals the valve after the working fluid has exited from the working fluid chamber into the well and the sealing means may also seal the aperture between the well and the well fluid chamber after the working fluid has exited from the working fluid chamber into the well.

14. Apparatus as claimed in any preceding claim, wherein a non-return valve is positioned in the drill string below the apparatus so that the working fluid is prevented from exiting through the bottom of the drill string.