FR2787827A1 - METHOD FOR ADJUSTING TO A OBJECTIVE VALUE OF A LEVEL OF DRILLING LIQUID IN AN EXTENSION TUBE OF A WELLBORE INSTALLATION AND DEVICE FOR CARRYING OUT SAID METHOD - Google Patents

Abstract

The invention concerns a method and a device for adjusting at a target value the bore fluid level in a riser (7) of a well (1) drilling plant, wherein said riser (7) encloses a hollow drill string (2) wherein is injected a bore liquid, said drill string (2) and said riser (7) defining an annular space (9) wherein the bore liquid rises after passing through a drilling bit (4) mounted at the end of said drill string (2). Said method consists in extracting the bore liquid from the annular space at an adjustable flow rate, characterised in that it further consists in directly introducing into the annular space (9), bore liquid at an adjustable introduction flow rate and operating on said extraction and introduction flow rates until the level of bore fluid in the riser (7) reaches the target value. The invention is particularly applicable in the oil industry, to operate drilling plants on land or at sea.

Description

DESCRIPTION

TECHNICAL AREA

  The present invention relates to the operation of installations used for drilling wells on land or at sea and of installations for carrying out maintenance operations on existing wells. It finds its application, in particular in the petroleum industry, to conduct well drilling installations of very different kinds, such as wells for the production of liquid or gaseous hydrocarbons on land or at sea, gas injection wells or water, waste injection wells, product storage wells as well as to conduct maintenance facilities for

these same wells.

STATE OF THE PRIOR ART

  An installation used for drilling subsea wells for the production of deep-sea hydrocarbons, of the type described in the document NPF Deepwater Conference, April 21-22, 1998, Rica Hotel, Kristiansund Stavanger NORWAY, entitled "New concepts for improved well control ", has a train of hollow rods, the lower end of which is located at the bottom of the sea is provided with a drilling tool and the upper end situated on the surface of the sea is

  coupled to rotational drive means.

  This drill string is surrounded in its upper part by an extension tube which extends from the bottom to the surface of the sea to form an annular space. One of the drilling operations consists in drilling a hole at the bottom of the sea using the drilling tool driven by the drill string. During this operation a drilling fluid is injected inside the drill string at its upper part

  to cool and lubricate the drilling tool.

  After passing through the tool the drilling fluid rises towards the surface

  from the sea in the annular space formed by the drill string and the extension tube.

  The drilling fluid also has the role of evacuating the cuttings produced during the drilling of the hole, of maintaining the walls of the hole and of balancing by its own weight the pressure of the fluids contained in the formations traversed in the drilling. The pressure at the bottom of the well exerted by the column of mud is proportional to the density of the mud and to the difference between the height of

  rising of the mud in the annular space and the bottom of the well.

  We can therefore vary these two parameters to adjust the pressure in

well bottom.

  The installation used for drilling comprises, in addition, pumping means connected to the extension tube below sea level, which suck the drilling fluid into the annular space and discharge it to the surface of the

sea in a storage tank.

  One method for operating such an installation consists in measuring the pressure at the bottom of the well by means of a suitable sensor and in adjusting this pressure by

  varying the level of ascent of the mud in the annular space.

  Another control method described in French patent application No. 98 10974 of 02/09/1998, consists in adjusting the pressure at the bottom of the well, from a calculated value of said pressure, by acting on the liquid flow rate.

  extracted by the pumping means connected to the extension tube.

  To implement these two methods it is necessary to have pumping means with variable flow capable of operating in immersion by

great depth.

  For example centrifugal pumps or positive displacement pumps

  driven by variable speed electric motors.

  Centrifugal pumps with fairly narrow optimal operating ranges are poorly suited to variable flow operations in large proportions. They also exhibit operating non-linearities which must be compensated for by complex control systems and which are manifested by variable response times with the operating flow and pressure. In both cases the reliability of the electric motors is insufficient to ensure an economically satisfactory service under the maintenance conditions.

  very difficult which are those of the drilling of underwater wells by great depth.

  The driving of the pumps by water turbines presents

similar disadvantages.

  In certain drilling conditions, such as those resulting from the arrival of formation fluids in the well being drilled, it is necessary to

  vary the liquid level in the annular space as quickly as possible.

  With the type of installations conducted according to the methods described above

  above the maximum speed of increase of the level of liquid in the annular space is obtained by reducing as much as possible the rate of extraction of drilling liquid, if possible by canceling it. This maximum speed is determined for a given well, on the one hand by the flow of drilling liquid injected into the drill string which is itself fixed by the drilling conditions, for example the speed of rotation of the tool, the nature of the training crossed and on the other hand possibly by the

  minimum flow rate of the pumping means of the extracted liquid.

  In situations in which it is necessary to rapidly lower the level of drilling liquid in the annular space, the means for pumping the extracted liquid must have a large reserve of power which is difficult to obtain with immersed equipment at great depth having

  good reliability and acceptable costs.

STATEMENT OF THE INVENTION

  The object of the present invention is precisely to remedy these drawbacks and in particular to provide a method and a device for adjusting the level of drilling fluid in an extension tube of a well drilling installation and an installation for producing maintenance operations on

existing wells.

  This method is particularly well suited to the operation of underwater oil production wells, gas or water injection wells,

  waste injection wells and product storage wells.

  It also applies to the conduct of wells on land, by means of the installation of an overhead extension tube equivalent to the extension tube of underwater wells. To this end, the present invention proposes a method for adjusting the level of drilling fluid in an extension tube of an installation for drilling a well to an objective value, installation in which said extension tube surrounds a train of hollow rods in which drilling fluid is injected, said drill string and said extension tube defining an annular space into which the drilling fluid rises after passing through a drilling tool mounted at the end of said drill string, said method consisting in extract drilling liquid from the annular space at an adjustable extraction rate and characterized in that it consists in addition of directly introducing into the annular space, drilling liquid at an adjustable introduction rate and act on said extraction and introduction rates until the level of liquid in the extension tube reaches

objective value.

  According to another characteristic of the method of the invention, the flow rate Qi of injecting mud into the drill string being determined by the conditions for carrying out the drilling, the flow rate for introducing drilling liquid directly into

  the annular space is between 0.2.Qi and 4.Qi.

  According to another characteristic of the method of the invention, the flow rate Qi of injecting mud into the drill string being determined by the conditions for carrying out the drilling, the flow rate for extracting drilling liquid from the annular space

is between 1.2.Qi and 5.Qi.

  According to another characteristic of the method of the invention, the introduction of drilling liquid directly into the annular space consists in pouring drilling liquid into the upper part of said annular space, above the

  drilling fluid contained in said space.

  According to another characteristic of the method of the invention, the introduction of drilling liquid directly into the annular space consists in injecting drilling liquid into the part of said annular space containing liquid

drilling.

  The subject of the invention is also a device for adjusting the level of drilling liquid to an objective value in an extension tube of a drilling installation for a well, installation in which said extension tube surrounds a train of hollow rods, means for injecting drilling fluid into said drill string, said drill string and said extension tube defining an annular space into which the drilling fluid rises after passing through a drilling tool mounted at the end of said train rods, said device comprising means for extracting drilling liquid from the annular space at an adjustable extraction rate and being characterized in that it further comprises means for direct introduction into the annular space, drilling fluid at an adjustable introduction rate, said extraction and introduction means acting on said rates until the

  liquid level in the extension tube reaches the target value.

  According to another characteristic of the device of the invention, the flow rate Qi of injecting mud into the drill string being determined by the conditions for carrying out the drilling, the flow rate for introducing drilling liquid directly into

  the annular space is between 0.2.Qi and 4.Qi.

  According to another characteristic of the device of the invention, the flow rate Qi of injecting mud into the drill string being determined by the conditions for carrying out the drilling, the flow rate for extracting drilling liquid from the annular space

is between 1.2.Qi and 5.Qi.

  According to another characteristic of the device of the invention, the means for direct introduction of drilling liquid into the annular space comprises means for pouring the drilling liquid into the upper part of said space

  annular, above the drilling fluid contained in said space.

  According to another characteristic of the device of the invention, the means for direct introduction of drilling liquid into the annular space comprise means of injecting the drilling liquid into the part of said annular space

containing drilling fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

  The invention will be better understood using the following description in

  reference to the appended drawings in which: FIG. 1 schematically represents a first embodiment in accordance with the description of the invention which can be used to regulate the level of drilling liquid in an extension tube of an installation for drilling an oil well under marine, by injecting drilling fluid into said tube

extender.

  FIG. 2 schematically represents a second embodiment in accordance with the description of the invention which can be used to adjust the level of drilling liquid in an extension tube of a drilling installation for an underwater oil well, by pouring liquid from drilling in said tube

extender.

  - Figure 3 shows schematically an installation for drilling a well on land equipped with a device according to the description of the invention usable for adjusting the level of drilling fluid in the extension tube of said installation, by pouring liquid from drilling in said tube

extender.

DETAILED DESCRIPTION OF THE INVENTION

  FIG. 1 schematically represents a first embodiment of the device of the invention usable for adjusting a level of drilling fluid in

  an extension tube of a drilling rig for an underwater oil well.

  The description of this device and its operating mode will allow

  to better understand the method of the invention.

  According to this first embodiment, the device of the invention comprises: - a train 2 of hollow cylindrical rods provided at its upper end with a head 3 for injecting drilling mud and at its lower end with a tool 4 for drilling, - mechanical means 5 for rotating the train 2 of rods, - a casing 6 which covers the upper part of the wall of the well 1 to consolidate it, an extension tube 7 connected to the casing 6, which extends between the bottom 27 and the surface 8 of the sea and surrounds the train 2 with rods, which defines with the latter an annular space 9 and which comprises an injection nozzle 10 located at a depth Hr as well as a nozzle 11 of extraction located at a depth He less than Hr, - a tank 12 of drilling mud which constitutes the drilling liquid, - means for injecting drilling liquid into the drill string 2, comprising a pump 13 for injecting mud in the rod train 2 which has an inlet 14 and an outlet 15, - a suction pipe 16 which connects the inlet 14 of the pump 13 for injecting mud into the train 2 of rods, to the mud tank 12, - a discharge pipe 17 which connects the outlet 15 from the pump 13 for injecting mud into the train 2 of rods, at the injection head 3, through a control valve 18 comprising an input 19 for controlling, a sensor 20 for measuring the flow rate of injected mud in the rod train 2, which delivers an electrical signal representative of this flow rate to an output 21, - means for extracting drilling liquid from the annular space 9, comprising a pump 32 for extracting mud from the annular space 9 which has an inlet 33 and an outlet 34, - a suction pipe 35 which connects the inlet 33 of the mud extraction pump 32 to the extraction nozzle 11, - a discharge pipe 36 which connects the outlet 34 of the mud extraction pump 32 in the annular space 9, to the mud tank 12, through a valve 37 for controlling the flow of mud extracted from the annular space 9, comprising an inlet 38 for controlling and through means 39 for filtering the mud, - a sensor 40 for measuring the flow rate of mud extracted from the annular space 9, which delivers an electrical signal representative of this flow rate to an output 41, means for direct introduction of drilling liquid into the annular space 9 comprising a pump 22 for injecting mud into the space 9 annular which has an inlet 23 and an outlet 24, - a suction pipe 25 which connects the inlet 23 of the slurry injection pump 22 in the annular space 9, to the mud tank 12, - a pipe 26 discharge which connects the outlet 24 of the pump 22 for injecting mud into the annular space 9, to the injection nozzle 10, through a valve 28 for controlling the flow of mud injected into the annular space 9 , comprising a control input 29, - a sensor 30 for measuring the inje mud flow side directly in the annular space 9, which delivers an electrical signal representative of this flow rate to an output 31, a sensor 42 for measuring the pressure in the annular space 9 at a depth Hp between Hr and He, which provides on an output 43 an electrical signal representative of this pressure and of the height to which the mud rises in the annular space for a quality of mud of given density, - a regulating device 44 comprising inputs 45, 46, 47 and 48 respectively connected to outputs 21, 31 and 41 of flow sensors 20, 30 and 40 and to output 43 of pressure sensor 42 and outputs 49, 50 and 51 connected respectively to inputs 19, 29 and 38 of valves 18, 28 and 37 for control, - control and display means 52 connected to the regulation device 44, The operation of drilling the well 1 at the bottom of the sea consists in practicing a

  hole in the formation by means of the tool 4 driven in rotation by the drill string.

  During this operation, fresh drilling mud stored in the tank is sucked by the pump 13 and injected inside the drill string via

of the injection head.

  The flow rate Qi of mud to be injected into the drill string is determined by the drilling conditions, in particular the nature of the rocks which constitute the formation crossed, the speed of rotation of the drilling tool 4, the pressure on the drilling tool. drilling by train 2 of rods. This flow rate value is introduced into the device 44 for regulation by an operator by means of the control and display means 52, as a reference value for the flow rate of injected sludge. This flow rate, measured by the sensor 20, is controlled by the set value Qi by the regulating device 44 which delivers on the output 49 an electrical signal representative of the

  position of the automatic valve 18.

  The mud injected into the drill string 2 flows from top to bottom and passes through the drilling tool 4 to cool and lubricate it. After passing through the tool the mud is loaded with the rock cuttings produced by the action of the tool 4

  on the formation and goes up in the annular space 9 to a HI level.

  During drilling, the pressure at the bottom of the well must be maintained at a value Pm such that the equilibrium with the pressure of the fluids contained in the formation and maintenance of the wall of the hole being produced is simultaneously ensured. This pressure Pm value depends on the nature of the well and varies as

  and as the drilling progresses.

  To obtain the pressure Pm at the bottom of the well, with a mud of given density Db, the level of liquid in the annular space must be set to a value

  Setpoint Hm such that Pm = Db.g.Hm, g being the terrestrial acceleration.

  The flow of mud injected into the train 2 of rods being regulated to the set value Qi, according to the method of the invention is injected into the annular space 9 at the depth Hr a flow Qint of mud by means of the pump 22 This flow rate Qint is equal to k.Qi, k being between 0 and 4. The value of k is introduced into the regulation device 44 by an operator by means of the control and display means 52. This value k is used by the regulation device 44 to calculate the flow rate setpoint Qint, and to control the flow rate of directly injected sludge, measured by the sensor 30, at this value by delivering on the

  output 50 an electrical signal for controlling the automatic valve 28.

  To maintain the sludge level reference value Hm in the annular space 9, the regulating device 44 controls the pressure measured in the annular space 9 by means of the sensor 42 to a pressure reference value calculated by applying the following formula: Pc = Db.g. [Hm (Hf - Hp)] In which: Pc represents the pressure in the annular space 9 measured by the sensor 42, Db represents the density of the mud, g represents the terrestrial acceleration Hm represents the height to which the mud goes up in the annular space 9 measured from the bottom of the well, Hf represents the depth of the well measured from the surface 8 of the sea, Hp represents the depth at which the sensor is installed 42 of

  pressure, measured from the surface 8 of the sea.

  and by delivering on output 51 an electrical signal for controlling the

  position of automatic valve 37.

  The increase in volume of the well, resulting from the advancement of the tool in the formation being negligible compared to the volume of mud in circulation, under steady conditions, the flow rate Qext of mud extraction from the annular space is substantially equal. to the sum of the flows injected on the one hand inside the train 2 of rods and on the other hand directly into the annular space 9, ie Qext = Qi + k.Qi

let Qext = (k + 1) Qi.

  When it is necessary, for operational reasons, for example when a formation gas comes into the well, to very quickly increase the level of mud in the annular space 9 to compensate for the reduction in pressure in downhole consecutive to this coming, the setpoint Hm of mud level in the annular space is modified either automatically or by an operator which has the effect of very quickly bringing the flow of mud extracted to

a null value.

  In this situation the flow Qi of mud injected into the rod train and the flow kQi of mud injected directly into the annular space 9 are added to

  raise the level in the annular space 9.

  The flow rate of sludge extracted being zero, the speed of rise of the level in the annular space is proportional to the total flow rate of slurry injected. Thus thanks to the invention this speed is (k + 1l) times higher than that obtained with the

  methods known before the invention.

  In addition, the maximum rate of rise of the level of mud in the annular space can be easily obtained instantaneously, by stopping the rate of extraction of mud by closing the automatic valve 37 and / or by stopping the

slurry extraction pump 32.

  When it is necessary to rapidly lower the level of mud in the annular space 9, for example in the event of a mud leak in the formation crossed, the operator can stop the pump 22 for injecting mud into the space 9 annular and / or close the valve 28 for injecting mud into the annular space, then instantly the difference between the mud extraction rate and the mud rate

  injected into the extension tube 7 is equal to [(k + 1) .Qi - Qi] or k.Qi.

  FIG. 2 schematically represents a second embodiment of the device of the invention which can be used to regulate a level of drilling liquid in an extension tube 7 of a drilling installation for an underwater oil well, which comprises the same elements as the device according to the first embodiment shown in FIG. 1, except the pipe 26, the end of which is no longer connected to the nozzle 10, but opens into the upper part of the annular space 9 above the level of mud, in order to allow the mud spill

  drilling in this part of the annular space 9.

  Thanks to the invention, the underwater mud extraction equipment operates in a narrow flow range, it can therefore be of a robust, reliable type,

  optimized for each drilling and controllable by simple control means.

  FIG. 3 schematically represents an installation for drilling an onshore oil well, which comprises an aerial extension tube 7 which extends the casing 6 and a device for adjusting the level of drilling liquid in this extension tube which comprises the same elements as the device according to the second

  embodiment of the invention shown in Figure 2.

  Thanks to the invention, for this type of well it is possible to act very quickly on the level of the drilling liquid to adjust the pressure at the bottom of

  well, without changing the density of the drilling fluid.

Claims (8)

  1 - Method for adjusting to an objective value the level of drilling fluid in an extension tube (7) of a well drilling installation, installation in which said extension tube (7) surrounds a train (2) of rods hollow into which drilling fluid is injected, said drill string (2) and said extension tube (7) defining an annular space (9) into which the drilling fluid rises after passing through a drilling tool mounted at the end of said drill string (2), said method consisting in extracting drilling liquid from the annular space (9) at an adjustable extraction rate and characterized in that it consists in addition of introducing directly into the annular space (9), drilling fluid at an adjustable introduction rate and act on said extraction and introduction rates until the level of liquid in the tube (7)   extender reaches the target value.   2- Method according to claim 1, characterized in that the flow rate Qi of injection of mud into the train (2) of rods being determined by the conditions for carrying out the drilling, the flow rate for introducing drilling liquid directly   in the annular space (9) is between 0.2.Qi and 4.Qi.   3- Method according to claim 1, characterized in that the flow rate Qi of injection of mud into the train (2) of rods being determined by the conditions for carrying out the drilling, the rate of extraction of drilling liquid from the space (9)   ring is between 1.2.Qi and 5.Qi.   4- Method according to any one of claims 1 to 3, characterized in that   that the introduction of drilling liquid directly into the annular space (9) consists in pouring drilling liquid into the upper part of said space   (9) annular, above the drilling liquid contained in said space.   - Method according to any one of claims 1 to 3, characterized in that   that the introduction of drilling liquid directly into the annular space (9) consists in injecting drilling liquid into the part of said annular space (9) containing drilling fluid.   6 - Device for adjusting the level of drilling fluid to an objective value in an extension tube (7) of a well drilling installation, installation in which said extension tube (7) surrounds a train (2) of rods hollow, means for injecting the drilling liquid into said drill string (2), said drill string (2) and said extension tube (7) defining an annular space (9) into which the drilling fluid rises after passage through a drilling tool mounted at the end of said drill string (2), said device comprising means for extracting drilling liquid from the annular space (9) at an adjustable extraction rate and is characterized in that it further comprises means for direct introduction into the annular space (9) of drilling liquid at an adjustable introduction rate, said extraction and introduction means acting on said rates up to 'that the liquid level in the tube (7)   extender reaches the target value.   7- Device according to claim 6, characterized in that the flow rate Qi of injection of mud into the train (2) of rods being determined by the conditions for carrying out the drilling, the rate of introduction of drilling liquid directly   in the annular space (9) is between 0.2.Qi and 4.Qi.   8 - Device according to claim 6, characterized in that the flow rate Qi of injection of mud into the train (2) of rods being determined by the conditions for carrying out the drilling, the rate of extraction of drilling liquid from the space (9)   ring is between 1.2.Qi and 5.Qi.   9 - Device according to any one of claims 6 to 8, characterized in that   the means for directly introducing drilling liquid into the annular space (9) comprises means for pouring the drilling liquid into the upper part of said annular space (9), above the drilling liquid contained in said space.   - Device according to any one of claims 6 to 8, characterized in that   the means for directly introducing drilling liquid into the annular space (9) comprise means for injecting drilling liquid into the part   said annular space (9) containing drilling liquid.