WO2000046480A1

WO2000046480A1 - Drillstring bypass valve

Info

Publication number: WO2000046480A1
Application number: PCT/EP2000/000945
Authority: WO
Inventors: Peter Airey; Mark Andrea; Michel Galbrun
Original assignee: Sofitech N.V.
Priority date: 1999-02-03
Filing date: 2000-02-02
Publication date: 2000-08-10
Also published as: GB2346397A; AU2670400A; GB9902342D0

Abstract

A discharge valve and a use thereof in a drilling operation is described, enabling the operator to select an intermediate section of a well where the return flow of the drilling fluid is boosted without intervention from the surface. The intermediate section can be for example cased section of a well.

Description

DRILLSTRING BYPASS VALVE

This invention relates to a method and an apparatus for enhancing the return flow of drilling fluids during drilling operations. Particularly it relates to a method and an apparatus for enhancing the return flow in intermediate large diameter sections of a subterranean wellbore.

BACKGROUND OF THE INVENTION

According to the standard practice of the industry, oil and gas wells are drilled in intervalls. First a section of the well is drilled by rotating a drillstring that carries at its bottom end a drill bit. While drilling, a fluid commonly referred to as "mud" is pumped through the drillstring. The drill bit has nozzle through which the drilling mud is ejected thereby cleaning the bit from cuttings and softening the bottom of the well to accelerate the drilling operation.

The mud returns to the surface through the annulus between the drillstring and the wall of the borehole. Under normal drilling conditions, the first section cannot be drilled to the desired subterranean location, the target depth. With increasing length or reach of the wellbore, the driller faces an ever- increasing risk that part of the formation surrounding the borehole collapses into the well and traps part of the drillstring. If the drillstring cannot be retrieved from the well, it is often necessary to abandon at least part of the borehole.

To reduce the risk of the collapse of formation into the borehole, the driller interrupts the drilling process at predetermined points and retrieves or trips out the drillstring. After the drillstring is removed from the borehole, a string on well tubulars, the casing string, is assembled and lowered into the wellbore. Prior to running the casing, it is sometimes necessary to enlarge the diameter of the borehole through an operation known as reaming.

After putting the casing in place, cement is squeezed through the casing into the annulus between casing and the wall of the wellbore. Casing string and cement provide a lining of the borehole that prevents a collapse of formation or a sudden influx of formation fluids into the borehole (kick) .

Having thus protected the first section of the wellbore, the drilling operation resumes and a susequent section of the well is drilled. This section is usually drilled with a much smaller diameter than the previous section. After reaching a certain depth or point, the drilling is stopped again to repeat the casing procedure described above.

Through repeated steps of drilling and casing the borehole is extended to the target formation in a fashion resembling a reverse telescope with sections of decreasing diameter stabilized with casing. The points at which a casing string terminates are known as casing points. The number and location of the casing points together with the respective diameters of the casing strings is known as casing program. A typical casing program may consists of running of 20 inch, 13 3/4 inch, 9 5/8 inch and 7 inch diameter casing. However, the final section of the borehole may be drilled and completed without a casing in what is known as "open hole" completion.

It can easily be seen that the on the return leg the mud flow is subject to a sudden change with respect to its flow conditions when entering from a small diameter section into a larger diameter section. In a large diameter section the velocity of the flow is reduced thus increasing the risk of cuttings deposition within the borehole. In a marine drilling environment this risk is compounded as above the seabed the mud is returned to the surface through special section of very large diameter pipes, known as marine riser pipes. For marine risers it has been proposed to improve the cuttings transport by adding an additional fluid line to the riser section. Through this "booster" line an additional amount of fluid is pumped into return path of the drilling fluid at the lower parts of the marine section or at the Blow Out Preventor (BOP) . The thus increased the flow facilitates the return of the cutting to the surface .

It is extremely difficult to extend the booster line into sections of the well lying below the sea bottom level. It is therefore an object of the invention to provide boosting capability to the mud return path below ground or sea bottom level .

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided a valve section connecting to joints of drill pipes such valve section providing an opening for drilling fluid to communicate from the interior of the drillstring into an annulus between the drillstring and the wall of the borehole, wherein said valve section comprises an switch element depending on the pressure differential between annulus and a valve element actuated by said switch element such that the valve is maintained in an open state within a predetermined range of pressure differentials and in a close state outside said range without intervention from the surface.

These and other features of the invention, preferred embodiments and variants thereof, possible applications and advantages will become appreciated and understood by those skilled in the art from the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the principle of the invention using a simplified example of a valve section;

FIG. 2 illustrates an application of the invention in a borehole;

FIGs . 3A,B show detailed views of a valve section in accordance with the invention;

FIGs. 4A-C show the valve section of FIG. 2 in various states of operation.

MODE(S) FOR CARRYING OUT THE INVENTION

In FIG. 1 part of a drillstring 10 is shown with a valve section 11 in accordance with the invention. The valve section comprises a sleeve moveable with a cage 13 formed by the inner contours of the wall of the valve section or sub 11. The sleeve is sealed against drilling fluid from the interior and exterior of the drillstring via several seals 14. The wall of the valve section has circulation ports 15 to allow fluid to communicate between the interior (high pressure side) and the exterior (low pressure side) of the drillstring 10. A second set of ports, pressure ports 16, are provided to communicate exterior, i.e annulus pressure to act on a shoulder 17 of the sleeve 12. The pressure reservoir 18 filled with an inert gas (nitrogen) act on a second shoulder 19. The sleeve member is further provided with circulation ports 151 that are designed to engage with circulation ports 15 thus opening a flow path through the drillstring.

In operation the pressure reservoir 18 is set on a surface to a predetermined pressure before lowering the valve section into the borehole. As during drilling the valve section enters deeper into the borehole the annulus pressure increases . When the annulus pressure exceeds the pre-set pressure in the pressure reservoir (and some additional friction forces) the sleeve is pushed into the direction of the circulation ports 15 until the internal circulation ports 151 are in line with the external circulation ports 15. Then drilling fluid pumped from the surface through the drillstring to the drill bit is partly diverted into the annulus at the location of the sub.

As the sub is pushed deeper following the progress of the drill bit, the annulus pressure continues to rise exerting an increasing pressure on the shoulder 17 of the sleeve. The nitrogen in the pressure reservoir is further compressed and the sleeve continues its movement, thereby pushing the internal circulation ports 151 past the external circulation ports 15. At a second pressure which again is determined by the pressure differential between the pressure reservoir 18 the valve is closed again and remains closed until the drilling operation ceases and the drillstring is retrieved to the surface (tripped out) .

FIG. 2 illustrates the use of the valve in a marine drilling operation. To facilitate the illustration it is assumed that one large section of the well has been drilled and casing has been suspended from a subsea BOP and cemented in. Subsequently a drillstring including a plurality of valve subs in accordance with the invention has been assembled and lowered (tripped) into the well to drill a small diameter hole. FIG 2 illustrates a stage of the drilling operation where a number (two) of valve subs have already passed the cased section and progressed into the small hole section.

According to the operating states of the valve section as explained above the pressure reservoir 18 has been set to a pressure that keeps the communication ports open in a pressure window that corresponds to the cased section. The ports are closed above and below that section. Accordingly, the third valve sub shown in FIG. 2 still located in the cased section is in an open state while the two valve sections in the small hole are in a closed state. As a consequence the mud return in the large diameter cased section is boosted by an additional contribution to the mudflow.

Referring now to FIG. 3A a cross-section is shown of another embodiment of a valve sub in accordance with the invention.

The valve section 30 comprises a bottom sub 31 and a top sub 32 with joints to connect onto conventional drill pipe joints. All moving parts of the valve section are contained with a third part, the main body 33, of the valve sub. The three parts of the valve section engage via threaded surfaces, thereby forming two circumferential pressure reference chambers 321, 322. The pressure chambers can be filled with pressurized fluid through the fill ports 323 and 324. A fluid communication channel leads from the first pressure reference chamber 321 to the housing chamber of a first spool valve 331. A second fluid communication channel leads from the second pressure reference chamber 322 to the housing chamber of a second spool valve 332.

The body is further provided with an annulus buffer piston 333 and in internal buffer piston 334. The internal buffer piston is subject to the pressure within the drillstring and transmits this pressure onto an internal hydraulic fluid chamber 335. The annulus buffer piston 333 is subject via the annulus pressure port 336 to the pressure in the annulus between the drillstring and the wall of the borehole. The annulus buffer piston 333 transmits the annulus pressure onto an second (external) hydraulic fluid chamber 337. Further hydraulic fluid channels 338 are provided to communicate hydraulic fluid between the elements of the valve sub in a manner described in more detail below.

The valve chamber 34 is shown again in FIG 3B, which is a cross- section perpendicular to the axis of the drillstring. The main valve chamber 34 houses the main valve to open and close the circulation port 341 through which drilling mud is discharged. A nozzle retainer nut 342 supports a tungsten carbide nozzle 343 as used for drill bit nozzles. A valve shutter 344 engages with the nozzle 343 operating similar to a known needle valve. A locking spring 345 forces the shutter into a default close position. Hydraulic pressure is transmitted onto a shoulder of the shutter 344 via hydraulic fluid channel 346 pushing the shutter against the spring, hence opening the valve.

The operational states of the valve sub 30 are shown in FIGs. 4A - C. The first reference chamber 321 is filled with nitrogen at a pressure at which the valve assumes its open state. The second reference chamber 322 is filled with nitrogen at a pressure at which the valve should resume its close state. The spring is set to lock the valve as long as the drilling fluid pressure within the drillstring is below a predetermined threshold. Hence the valve can be forced into a close position by reducing the pumping pressure or ceasing pumping.

In FIG. 4A the valve sub is shown in its initial close state assuming that the annulus pressure on the annulus buffer piston is smaller that the counter-acting pressure in the first reference chamber 321. The valve shutter receives annulus pressure directly through the circulation port and through the external hydraulic chamber 337 as the first and second spool valve 331 and 332 are set to communicate the annulus pressure to the valve chamber 34.

As the annulus pressure exceeds the pressure in the first reference chamber, the first spool valve 331 moves and thus interrupts the communication between the external hydraulic chamber 337 and the valve chamber 34. Simultaneously, it opens a fluid channel between the internal hydraulic chamber 335 and the valve chamber. The internal pressure is assumed to be high enough to push the valve shutter 344 against the spring 345 thus opening the valve as shown in FIG. 4B. As the valve section is pushed deeper into the well with the advancing drill bit, the annulus pressure exceeds at a second location the pressure in the second reference chamber 322. Then, the second spool valve 332 moves and thus interrupts the communication between the internal hydraulic chamber 335 and the valve chamber 34. Simultaneously, it re-opens a fluid channel between the external hydraulic chamber 337 and the valve chamber. The annulus pressure is not sufficient to balance the force of the spring 345, so that the valve shutter 344 closes against the nozzle 343 as shown in FIG. 4C.

The invention seeks to include further variants of the invention such as modifying the nozzle diameter of the valve in accordance with the location of the sub in the drillstring. Other parameter that can be modified according to the location of the sub are the pre-set pressure in the pressure reservoirs or the force of the springs used to close the valves.

Furthermore it is feasible to use the valve sections of the present invention in combination with dual-wall drill pipes, known as such in the art, by integrating the valve section into one of the walls, thereby enabling a communication of fluid between inner pipe and outer pipe or between outer pipe and annulus .

The operational safety of the device can be further improved by providing a lock-out mechanism that overrides the settings of the valve mechanism. Such a lock-out can be actuated for example by reversing the rotation of the drillstring thereby releasing a spring-loaded pin. The pin can be used to force the valve into a close position.

Claims

1. A method of drilling a well comprising the steps of: providing a hollow drillstring with at least one valve section; lowering into the well said drillstring with a drill bit attached to its lower end; pumping drilling fluid through said drillstring; drilling further said well; while drilling, changing without further intervention from the surface the state of said valve section from close to open at a first predetermined pressure in the annulus between the drillstring and the wall of the well; while drilling, changing without further intervention from the surface the state of said valve section from open to close at a second predetermined pressure in the annulus between the drillstring and the wall of the well, said second pressure being higher than said first pressure, thereby causing said valve section to be in an open state within an intermediate section of said well; discharging in said intermediate section part of said drilling fluid through said valve section.

2. The method of claim 1, wherein the pressures are determined such that the intermediate section coincides with a section of the well having a larger diameter than the section under drilling.

3. The method of claim 2, wherein the intermediate section comprises at least part of a cased section of the well.

4. The method of claim 1, comprising the step of using a plurality of valve sections at different locations of the drillstring .

The method of claim 4, comprising the step of providing said valve sections with discharge nozzles of varying size.

6. A discharge valve to improve a return flow of drilling fluid to the surface of a well comprising; a main body with upper and lower joints to engage with corresponding joints of drill pipe; at least one pressure port to communicate annulus pressure into said main body; at least one circulation port providing in an open state a fluid path between the interior of said main body to the exterior of said main body; at least one reference pressure chambers to be pre-set at the surface; a valve mechanism to open and close said at least one circulation path; and fluid filled communication channels communicating said annular pressure to said valve mechanism.

7. The discharge valve of claim 6, comprising at least two reference pressures chambers .

8. The discharge valve of claim 6, wherein the reference pressure chamber is filled under operating conditions with inert gas .

9. The discharge valve of claim 6, wherein the valve mechanism comprises restoring force means to maintain a default close state.

10. The discharge valve of claim 6, included in a dual-wall drill pipe.