At-the-bit mud loss treatment

Abstract

A while drilling mud loss treatment method includes providing a drilling tool main body with a through bore connected to an above arranged wired drill pipe string with a communication line to a topsides monitoring and control system, the drilling tool main body connected to a below arranged one or more drill collar sections with a lower of said drill collar sections connected to a drill bit, and drilling in a well. The main body is provided with an annular tank with a swellable sealant and the annular tank has a valve to an outlet to the through bore. A control system in the main body receives MWD sensor signals from an MWD sensor system and controls the valve having a valve actuator. The control system is, during drilling, running a monitoring and control algorithm using the signals as input for detecting an undesired mud loss state during drilling, and, if a mud loss state is detected, to command said valve actuator to open said valve upon detecting an undesired mud loss state, so as for ejecting said swellable sealant to said through bore.

Claims

1. A mud loss treatment drilling tool, comprising: a main body with a through bore, and an upper tool joint to connect to an above arranged drill pipe string with an associated communication line to and from a topsides monitoring and control system; and a lower tool joint to connect to a below arranged one or more drill collar sections with a lower of said drill collar sections connected to a drill bit with nozzles, wherein said main body is provided with an annular tank with a swellable sealant, wherein said annular tank has an outlet to said through bore, and a valve system having a first valve actuator operable in response to a detection of an undesired mud loss state, and said first valve actuator is operable to allow said annular tank to eject said swellable sealant to said through bore in response to the detection of the undesired mud loss state, and wherein said swellable sealant is arranged, when ejected from said outlet, to contact said drilling mud in said through bore, to start reacting to swell during the time it which said drilling mud with said swellable sealant takes to pass out through the drilling bit nozzles, and continue to swell and set while said drilling mud being placed in a fracture extending from a borehole being drilled by said drill bit.

2. The mud loss treatment tool of claim 1, wherein said valve system comprises a second valve actuator for an inlet valve operable to allow drilling fluid in from the through bore, and wherein said first valve actuator is configured for activating an outlet valve to release said swellable sealant to said main bore.

3. The mud loss treatment drilling tool of claim 2, wherein said annular tank is provided with a piston arranged for driving out said swellable sealant to said valve system.

4. The mud loss treatment drilling tool of claim 2, further comprising at least one sensor selected from the group consisting of: a bore mud pressure sensor; a bore mud flow velocity sensor (ultrasound Doppler); an annulus mud pressure sensor; a mud pressure bore/annulus differential pressure (Pb-Pa) sensor; an annulus mud velocity sensor (ultrasound Doppler); a bore temperature sensor; an annulus temperature sensor; a temperature bore/annulus differential temperature (Ta-Tb) sensor; a bore mud density sensor; and an annulus mud density sensor.

5. The mud loss treatment tool of claim 1, wherein said annular tank has said first valve actuator for a diverter valve arranged near an upper end of said annular tank in said through bore to divert drilling mud to an upper end of said annular tank through an inlet and said outlet is arranged near a lower end of said annular tank back to said through bore, so as for flushing said swellable sealant into said through bore.

6. The mud loss treatment drilling tool of claim 5, further comprising at least one sensor selected from the group consisting of: a bore mud pressure sensor; a bore mud flow velocity sensor (ultrasound Doppler); an annulus mud pressure sensor; a mud pressure bore/annulus differential pressure (Pb-Pa) sensor; an annulus mud velocity sensor (ultrasound Doppler); a bore temperature sensor; an annulus temperature sensor; a temperature bore/annulus differential temperature (Ta-Tb) sensor; a bore mud density sensor; and an annulus mud density sensor.

7. The mud loss treatment drilling tool of claim 1, wherein said annular tank is provided with a piston arranged for driving out said swellable sealant to said valve system.

8. The mud loss treatment drilling tool of claim 7, wherein said annular tank is provided with an inlet valve or pump with a mud balancing pressure inlet from said through bore near an upper end of said annular tank and provided with an inlet valve actuator, said pump or valve contributing to driving said piston.

9. The mud loss treatment drilling tool of claim 7, further comprising at least one sensor selected from the group consisting of: a bore mud pressure sensor; a bore mud flow velocity sensor (ultrasound Doppler); an annulus mud pressure sensor; a mud pressure bore/annulus differential pressure (Pb-Pa) sensor; an annulus mud velocity sensor (ultrasound Doppler); a bore temperature sensor; an annulus temperature sensor; a temperature bore/annulus differential temperature (Ta-Tb) sensor; a bore mud density sensor; and an annulus mud density sensor.

10. The mud loss treatment drilling tool of claim 1, further comprising at least one sensor selected from the group consisting of: a bore mud pressure sensor; a bore mud flow velocity sensor (ultrasound Doppler); an annulus mud pressure sensor; a mud pressure bore/annulus differential pressure (Pb-Pa) sensor; an annulus mud velocity sensor (ultrasound Doppler); a bore temperature sensor; an annulus temperature sensor; a temperature bore/annulus differential temperature (Ta-Tb) sensor; a bore mud density sensor; and an annulus mud density sensor.

11. The mud loss treatment drilling tool of claim 1, wherein said detection of an undesired mud loss state is based on a signal representing said undesired mud loss state communicated via a downhole modem to a surface modem to a topside monitoring and control system, such that a surface triggering command signal is transmitted to said first valve actuator to open said valve system for ejecting said swellable sealant.

12. The mud loss treatment drilling tool of claim 1, wherein said communication line associated with said drilling pipe string is a wired line of said drilling pipe string, said wired line connected between said tool and a topsides monitoring and control system.

13. The mud loss treatment drilling tool of claim 1, wherein said communication line associated with said drilling pipe string is a mud pulse telemetry system in the annulus of said drilling pipe string, said mud pulse telemetry system signalling between said tool and a topsides monitoring and control system.

14. A while drilling mud loss treatment method comprising: providing a drilling tool main body with a through bore to an above arranged drill pipe string with a communication line to a topsides monitoring and control system, said main body provided with an annular tank, wherein said drilling tool main body is connected to a below arranged one or more drill collar sections with a lower of said drill collar sections connected to a drill bit; and drilling in a well, wherein said annular tank is provided with a swellable sealant, wherein said annular tank has a valve system to an outlet to said through bore, said valve system having a first valve actuator, wherein said first valve actuator is operable to activate said valve system upon detecting an undesired mud loss state, so as for ejecting said swellable sealant to said through bore, and wherein said swellable sealant is arranged for, when ejected from said outlet to said drilling mud, to start reacting with said drilling mud to swell during the time which said drilling mud with a portion of said swellable sealant takes to pass through the drilling bit nozzles, and continue to swell and set while said drilling mud being placed in a fracture extending from a borehole being drilled by said drill bit.

15. The while drilling mud loss treatment method of claim 14, wherein a signal representing said detected undesired mud loss state is transmitted via a downhole modem to a surface modem to said topsides monitoring and control system, and in response, a surface triggering confirmation command signal is transmitted to said first valve actuator to activate said valve system for allowing the tank to eject said swellable sealant.

16. The while drilling mud loss treatment method of claim 14, wherein after having ejected said swellable sealant and said swellable sealant has halted said undesired mud loss, circulating out remaining swellable sealant not having entered into fractures.

17. The while drilling mud loss treatment method of claim 14, further comprising continuing drilling beyond the well depth in which said undesired mud loss state occurred.

18. The while drilling mud loss treatment method according to claim 14, further comprising the steps of: upon detecting the undesired mud loss status, sending said surface triggering confirmation command signal down to said first valve actuator, making a pre-determined series of drill string rotations, selectable among one or more of from the group consisting of: halting rotation and reversing it; conducting a series of RH and LH rotations; conducting a series of RH rotations interrupted by periods of halt of rotations; increasing WOB and decreasing WOB in a predetermined pattern; and running at a predefined rotation speed RPM for a pre-determined period of time.

19. The while drilling mud loss treatment method according to claim 14, comprising upon detecting the undesired mud loss status, also based on measurements conducted on the surface, sending said surface triggering confirmation command signal down to said first valve actuator.

20. The while drilling mud loss treatment method according to claim 14, comprising sending signals from the tools to the surface, or signals representing surface-based measurements, or said surface triggering confirmation command signal on the pipe string.

Description

BRIEF FIGURE CAPTIONS

(1) FIG. 1 is a rough sketch of an embodiment of the invention with a bottom hole assembly comprising, from bottom to top, a drill bit drilling and encountering an induced or natural fracture (F.sub.F) wherein mud loss occurs; a series of drill collars, and a mud loss treatment tool (1) according to the invention. A main bore (101) is arranged through the tool (1). The mud loss treatment tool (1) has a concentric tank (10) arranged about the main bore (101), the tank (10) contains a swellable sealant (5) arranged for being injected to said main bore (101) and to be ejected through the drill bit nozzles together with drilling mud in order to start swelling and “get lost” into said fracture and partly or fully block throats in said fracture.

(2) FIG. 2 is an enlarged detail of an embodiment of the mud loss treatment tool (1). In FIG. 2, the mud loss treatment tool (1) is shown as been designed similar to a drill collar, i.e. with a similar diameter and pin and box connections similar to those of a drill collar. A different diameter may be used. The swellable sealant (5) is released upon the tool's control system (13) having detected an undesired mud loss state, and the swellable sealant (5) is carried along with the drilling mud in the main bore down through the drill collars and out through the nozzles of the drill bit, whereby it will follow the flow out to the fractures where the undesired loss occurs. There it will swell to form a gel and in the throats of the fractures may temporarily or permanently halt and cure the mud loss so as for drilling to continue undisturbed. The embodiment of the invention shown in FIG. 2 has an inlet valve/pump (124) for allowing drilling mud in from the main bore (101) and an outlet valve (12)/pump for releasing the swellable sealant to the main bore (101).

(3) FIGS. 3a and 3b are enlarged details of another embodiment of the mud loss treatment tool (1). In these Figures, the mud loss treatment tool (1) are shown as been designed similar to a drill collar. The embodiment shown here has a diverter valve (127) in the main bore in order to divert drilling mud flow from the main bore (101) into an upper inlet (129) to displace swellable sealant (5) in the tank (10) to be released through a lower outlet (120) back into the main bore (101). In a further embodiment the inlet (129) and the outlet (120) may be provided with a shear membrane rupturing upon a differential pressure across them. FIG. 3a shows the mud loss treatment tool (1) when the diverter is not activated, and FIG. 3b shows the mud loss treatment tool (1) when the diverter is activated.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(4) The invention is a mud loss treatment drilling tool arranged for ejecting a swellable sealant (5) while drilling, if detecting an undesired mud loss state. Thus the invention is also a method of ejecting a swellable sealant (5) to undesired fractures occurring while drilling, for halting undesired mud loss. The inventors have loosely compared the mud loss drilling tool to an airbag, but this tool goes beyond comparison, it may halt and cure the undesired mud loss state, but it also allows continued drilling “as if nothing had happened”. A major advantage of the invention is, that after having controlled an undesired mud loss, i.e. after and during controlling the undesired mud loss using the present invention, without interrupting the drilling or retrieving the drilling string, the drilling may continue essentially uninterrupted by the occurrence of the undesired mud loss. This is a significant advantage over the background art.

(5) The device:

(6) The invention is a mud loss treatment drilling tool comprising a main body (1) with a through bore (101), an upper tooljoint (101U) to an above arranged drill pipe string (0) with a communication line (01) to a topsides monitoring and control system (02), a lower tooljoint (101L) to a below arranged one or more drill collar sections (2) with a lower of said drill collar sections (2) connected to a drill bit (3). The main body (1) is provided with an annular tank (10) with a swellable sealant (5). The annular tank (10) has a valve system (12) allowing the swellable sealant (5) to be released from the tank (10) through an outlet (120) to said through bore (101). The valve system (12) has a valve actuator (121, 128) controlled by a control system (13) receiving MWD sensor signals from an MWD sensor system (11). The control system (13) and said MWD sensor system (11) are powered by an energy source (14), wherein said control system (13) and said MWD sensor system (11) are arranged within said main body (1). The control system (13) has an algorithm (131) arranged for processing at least the MWD sensor signals in order to command the valve actuator (121, 128) to activate the valve system (12) upon having detected an undesired mud loss state, so as for allowing the tank (10) ejecting said swellable sealant (5) to said through bore (101).

(7) In an embodiment of the invention, the energy source (14) is arranged within the tool body (1). In an embodiment of the invention, the energy source (14), the downhole modem and communication terminal (15) is arranged in the annulus part of the mud loss treatment tool body (1). The components are arranged outside the main central bore (101). In an embodiment of the invention the energy source (14) is a battery. The energy source (14) is arranged adjacent to the control system (13) and the control system is connected to the valve actuators (121, 128) and to the MWD sensor system (11). In an embodiment the MWD sensor system (11) is connected to one or more internal bore sensors (111) and one or more annulus arranged sensors (112), see FIG. 1.

(8) In an embodiment of the invention, mud (m) is allowed into the tank (10) behind a piston (126), which again forces out the swellable sealant, see FIG. 2.

(9) The method:

(10) Analoguely, the corresponding while drilling mud loss treatment method comprises providing a drilling tool main body (1) with a through bore (101) connected to an above arranged drill pipe string (0) with an associated communication line (01) to a topsides monitoring and control system (02), the drilling tool main body (1) connected to a below arranged one or more drill collar sections (2) with a lower of said drill collar sections (2) connected to a drill bit (3), and drilling in a well. The main body (1) is provided with an annular tank (10) with a swellable sealant (5) and the annular tank (10) has a valve system (12) for activating release of the swellable sealant (5) to an outlet (120) to the through bore (101). A control system in the main body (1) receives MWD sensor signals from an MWD sensor system (11) in the main body (1). The control system (13) and MWD sensor system (11) both receives energy from an energy source (14) in said main body. The control system (13) controls the valve system (12) having a valve actuator (121, 128) to release the swellable sealant (5) to the main bore (101). The control system (13) is, during drilling, running a monitoring and control algorithm (131) using the signals as input for detecting an undesired mud loss state during drilling, and, if a mud loss state is detected, to command said valve actuator (121) to activate said valve system (12) upon detecting an undesired mud loss state, so as for ejecting said swellable sealant (5) from the tank (10) to said through bore (101).

(11) The valve system (12) may be controlled by the control system (13) to close after a given dose of the swellable sealant (5) from the tank so as for being prepared to repeat the remedying operation if further mud loss states are detected either at the same depth as the first release of swellable sealant occurs or further down, or it may be designed to go “all in” and eject the entire contents of the tank (10) in one round. This could be pre-programmed in the control system depending on the risk assessment of the well under drilling based on its own and neighbouring wells history. If being emptied the tool should be routinely replenished with new swellable sealant (5) when being retrieved to the surface.

(12) In an embodiment of the invention, the swellable sealant (5) is arranged for, when ejected from said outlet (120) to said drilling mud, to start reacting with said drilling mud to swell during the time it takes said drilling mud with a portion of said swellable sealant (5) to pass through the drilling bit nozzles, and continue to swell and set while said drilling mud being placed in a fracture extending from a borehole being drilled by said drill bit (3). Further, the annular tank (10) may be provided with a piston (126) for driving out said swellable sealant (5) to the outlet valve of said valve system (12).

(13) As an example, the tank (10) may hold 50-200 litres, preferably 100 litres, of swellable agent (5). The swellable agent (5) will start swelling when in contact with water in the drilling mud or in the fracture fluid. The swellable agent (5) may expand about 100 times when in contact with water, and will efficiently block throats in fractures.

(14) In an embodiment of the invention, the annular tank (10) is provided with an inlet valve or pump (124) with a mud balancing pressure inlet (129) from said central bore (101) near an upper end of said annular tank (10) and provided with an inlet valve actuator (123), the pump or valve contributing to driving said piston (126). A small controlled explosively or otherwise expanding charge may also be used to create pressure to make the piston (126) drive out the swellable sealant (5). In this embodiment the piston as such may be optional. Please note that the use of a piston which is displaced by inflowing drilling mud will isolate the incoming drilling mud from the displaced swellable sealant (5) thus preventing reaction of the mud and swellable sealant within the confines of the tank (10) itself, which will safeguard the portioning opion mentioned elsewhere in this description.

(15) The MWD sensor system (11) is provided with one or more of internal bore sensors (111) and/or annulus sensors (112), such as: bore mud pressure (111Pb) sensor bore mud flow velocity (111Vb) sensor (ultrasonic Doppler) annulus mud pressure (112Pa) sensor, mud pressure bore/annulus differential pressure (Pb-Pa) sensor annulus mud velocity (112Va) sensor (ultrasonic Doppler) bore temperature (111Tb) sensor annulus temperature (112Ta) sensor, temperature bore/annulus differential temperature (Ta-Tb) sensor bore mud density (111Rho b) sensor annulus mud density (112Rho a) sensor.

(16) With the above sensors it is possible to detect a sudden loss of mud to a fracture. A fracture may occur naturally or be induced due to overbalanced pressure. Anyway, the drill bit suddenly comes in communication with a fracture, and the desired circulation of drilling mud (F1) down the drill pipe string, the drill collars and out through nozzles in the drill bit, further with the drilling mud carrying away heat and cuttings up along the drill collar annulus, is reduced, and part of the drilling mud is lost to the fracture. The annulus mud pressure (112Pa) may drop or may drop relative to the bore mud pressure (111Pb). The annulus velocity (112Va) (which may be measured using an ultrasonic Doppler) of the return drilling mud may drop due to the reduced flow of drilling mud. The reduced return of drilling mud may incur an increased annulus temperature (112Ta) while drilling. All or some of these parameters may be used in an algorithm for detecting an undesired mud loss state during drilling.

(17) In an embodiment of the invention the control system (13) is arranged for communicating a signal representing said undesired mud loss state via a communication terminal or downhole modem (15) to a surface modem (415) to a surface control system, so as for receiving a surface triggering command signal to said valve actuator (121) to open said valve (12) for ejecting said swellable sealant (5). This may give the driller a choice to assess the situation, possibly considering surface measurements such as circulation rate and return flow volume, before eventually releasing the trigger for ejecting the swelling sealing agent (5) into the assumed arising fractures.

(18) In an embodiment of the invention the drill pipe string (0) is wired, for example with wired signal transmission or otherwise signal transmission. This provides two advantages: firstly, one is always able to communicate with the tool from the surface even when a severe mud loss is occurring; otherwise the mud signal path is discontinued. Secondly, a wired pipe allows a distributed sensor arrangement along the drill pipe string (0) in addition to the sensor arrangement in the tool.

(19) The main body (1) of the mud loss treatment drilling tool does not necessarily have to be the top section of the borehole assembly BHA. The main body (1) may in an embodiment have its upper tooljoint (101U) connected not directly to an above arranged wired or otherwise signalling drill pipe string (0) with a communication line (01) to a topsides monitoring and control system (02), but connected via a drill collar (2) which is also a wired pipe or otherwise signalling system provided with said communication line (01).

(20) The control system (13) algorithm (131) receives the MWD sensor signals during drilling in order to determine an undesired mud loss state. When having determined whether an undesired mud loss state has occurred, the algorithm (131) issues a command signal to said valve actuator (121) to activate the valve system (12) to release the swellable sealant (5) from the tank (10).

(21) In case of the drill bit arriving at a depth of which the borehole comes into contact with a natural fracture, or a fracture is induced from the borehole due to the mud pressure involved in the drilling process, or a combination of the two, an undesired and significant mud loss may suddenly occur. Such a sudden drilling mud loss may be detected as a sudden reduction in the annulus mud pressure (Pa) due to the leakage of drilling mud into the surrounding fractures.

(22) When the valve system (12) opens the outlet (120) of the annular tank (10) the swellable sealant (5) comes in contact with the drilling mud.

(23) In an embodiment of the invention the swellable sealant (5) is arranged for, when ejected from said outlet (120) to said drilling mud, to start reacting with said drilling mud to swell during the time it takes said drilling mud with a portion of said swellable sealant (5) to pass through the drilling bit nozzles, and continue to swell and set while said drilling mud being placed in a fracture extending from a borehole being drilled by said drill bit (3).

(24) In an embodiment the control system may (13) act autonomously, said local downhole control system (13) receiving signals from its local sensors such as the above mentioned sensed by the MWD sensor system (11) with the internal bore sensors (111) and/or annulus sensors (112), such as: bore mud pressure (111Pb) sensor bore mud flow velocity (111Vb) sensor (ultrasonic Doppler) annulus mud pressure (112Pa) sensor, mud pressure bore/annulus differential pressure (Pb-Pa) sensor annulus mud velocity (112Va) sensor (ultrasonic Doppler) bore temperature (111Tb) sensor annulus temperature (112Ta) sensor, temperature bore/annulus differential temperature (Ta-Tb) sensor bore mud density (111Rho b) sensor annulus mud density (112Rho a) sensor.

(25) and determines that an undesired mud loss state is occurring. Then the control system (13) may send a triggering command signal (ST) to said valve actuator (121) to activate said valve system (12) for ejecting said swellable sealant (5).

(26) However, such an autonomous control system may be undesirable for several reasons: it may trigger falsely or prematurely based on un-anticipated mud flow states mis-interpreted by the local algorithm.

(27) Moreover, a downhole autonomous control system (13) could advantageously have mud flow signals input also as measured at topside, such as Stand pipe pressure, bar Flow rate in, Ipm Flow rate out, Ipm Traveling block position.

(28) Therefore, in an embodiment of the invention, the control system (13) sends a mud loss state signal (SL) representing said detected undesired mud loss state via a downhole modem (15) (optical, electrical or acoustic) to a surface modem (415) to a surface control system, and awaits receiving a surface triggering confirmation command signal (SC) to said valve actuator (121) to activate said valve system (12) for allowing ejecting said swellable sealant (5).

(29) In case of a loss of mud to the formation or the fractures, there is a risk of losing mud signalling contact with the bottomhole assembly. Therefore, in an embodiment of the invention, when having determined at the surface that a loss of mud situation is occurring, regardless of the downhole control system is able to send the mud loss state signal (SL) representing said detected undesired mud loss state via a downhole modem (15) to a surface modem (415) to a surface control system or not (the mud signal path may have been temporarily lost) one may send signals down to the bottomhole assembly by making a pre-determined series of rotations, selectable among one or more of the following: halting rotation and reversing it, conducting a series of RH and LH rotations conducting a series of RH rotations interrupted by periods of halt of rotations increasing WOB and decreasing WOB in a predetermined pattern. running at a predefined rotation speed RPM for a pre-determined period of time.

(30) This will enable the driller to command or trigger the bottomhole assembly regardless of the possible absence of other communication channels.

(31) In an embodiment of the invention, after having ejected said swellable sealant (5) and said swellable sealant (5) has halted said undesired mud loss, one may circulate out remaining swellable sealant (5) not having entered into fractures.

(32) The swellable sealant (5) is arranged for swelling and setting within the undesired fractures in the rock formations being drilled through, in order to prevent further outflux of drilling mud from the borehole to the fractures. It may even be designed for hardening after setting in the fractures. However, the resulting shear resistance may develop gradually so as for allowing the swelled agent (5) mixed with drilling mud and rock fluids to set and block the apertures in the fractures, while the shear resistance of the swelling agent (5) mixed with drilling mud around the drill bit, the drill collars and the drilling string will not be high enough to prevent continued rotation and circulation out of such remaining swelling agent. Otherwise the drill string would get stuck.

(33) In an embodiment of the invention one may continue drilling beyond the well depth in which said undesired mud loss state occurred. This is a major advantage of the invention: after having controlled the undesired mud loss, i.e. after and during controlling the undesired mud loss using the present invention, without interrupting the rotation of the drilling string, the drilling may continue essentially uninterrupted by the occurrence of the undesired mud loss.