US20030029611A1 - System and method for actuating a subterranean valve to terminate a reverse cementing operation - Google Patents

A system and method for closing a subterranean valve (22) to terminate a reverse cementing operation is disclosed. The system comprises an interrogator (44) operably associated with the valve (22) that detects at least one detectable member (52) that is associated with an interface (50) between a first fluid (48) and a cement composition (54) that is pumped through an annulus (26) between a pipe string (20) and a wellbore (18). The detectable member (50) is detectable by the interrogator (44) when the detectable member (50) comes within communicative proximity with the interrogator (44). Once the interrogator (44) detects the detectable member (50), the interrogator (44) sends a signal indicating it is time to close the valve (22), thereby terminating the cementing process and allowing the cement (54) to set in the annulus (26) into a hard, substantially impermeable mass.

TECHNICAL FIELD OF THE INVENTION

• The present invention relates, in general, to controlling the actuation of a subterranean valve and, in particular, to a system and method for actuating a subterranean valve upon confirmation that cement has reached the far end of the annulus between the casing and the wellbore during a reverse cementing operation.

BACKGROUND OF THE INVENTION

• Without limiting the scope of the present invention, its background will be described with reference to cementing a string of casing within a wellbore as an example.

• In primary cementing operations carried out in oil and gas wells, a hydraulic cement composition is disposed between the walls of the wellbore and the exterior of a pipe string, such as a casing string, that is positioned within the wellbore. The cement composition is permitted to set in the annulus thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe in the wellbore and bonds the pipe to the walls of the wellbore whereby the undesirable migration of fluids between zones or formations penetrated by the wellbore is prevented.

• One method of primary cementing involves pumping the cement composition down through the casing and then up through the annulus. In this method, the volume of cement required to fill the annulus must be calculated. Once the calculated volume of cement has been pumped into the casing, a cement plug is placed in the casing. A drilling mud is then pumped behind the cement plug such that the cement is forced into and up the annulus from the far end of the casing string to the surface or other desired depth. When the cement plug reaches a float shoe disposed proximate the far end of the casing, the cement should have filled the entire volume of the annulus. At this point, the cement is allowed to dry in the annulus into the hard, substantially impermeable mass.

• It has been found, however, that due to the high pressure at which the cement must be pumped, at a pressure above the hydrostatic pressure of the cement column in the annulus plus the friction pressure of the system, fluid from the cement composition may leak off into a low pressure zone traversed by the wellbore. When such leak off occurs, the remainder of the cement composition near this low pressure zone flash freezes and sets at that location in the annulus. Once this occurs, additional cement cannot be pumped past this location and all the cement in the system sets. Thereafter, remedial cementing operations, commonly referred to as squeeze cementing, must be used to place cement in the remainder of the annulus. In addition, a large mass of cement that was intended to be placed in the annulus must now be drilled out of the casing.

• Accordingly, prior art attempts have been made to avoid the problems associated with fluid leak off into low pressure zones during cementing operations. One method of avoiding such problems is called reverse cementing wherein the cement composition is pumped directly into the annulus. Using this approach, the pressure required to pump the cement to the far end of the annulus is much lower than that required in conventional cementing operations. Thus, the likelihood of flash freezing the cement in the annulus before the entire annulus is filled with cement is significantly reduced.

• It has been found, however, that with reverse cementing it is necessary to identify when the cement begins to enter the far end of the casing such that the cement pumps may be shut off. Continuing to pump cement into the annulus after cement has reached the far end forces cement into the casing, which in turn may necessitate a drill out operation.

• One method of identifying when the cement has reached the far end of the annulus involves running a neutron density tool down the casing on an electric line. The neutron density tool monitors the density out to a predetermined depth into the formation. When the cement begins to replace the drilling mud in the annulus adjacent to the neutron density tool, the neutron density tool senses the change in density and reports to the surface that it is time to stop pumping additional cement into the annulus. Another method of identifying when the cement has reached the far end of the annulus involves running a resistivity tool and a wireless telemetry system down the casing on a wireline. The resistivity tool monitors the resistivity of the fluid in the casing such that when the cement begins to replace the drilling mud in the casing, a wireless signal is sent to the surface indicating it is time to stop pumping additional cement into the annulus.

• It has been found, however, that use of such retrievable tool systems is prohibitively expensive. In fact, numerous neutron density tools and resistivity tools have been ruined during such operations as a result of the cement entering the far end of the casing and contacting these tools.

• Therefore, a need has arisen for a system and method for cementing the annulus between the wellbore and the casing that does not require pumping the cement at pressures that allow for leak off into low pressure zones. A need has also arisen for such a system and method that identify when to stop pumping additional cement into the wellbore. Further, a need has arisen for such a system and method that do not require the use of expensive equipment including tools that must be retrieved from the well once the cementing operation is complete.

SUMMARY OF THE INVENTION

• The present invention disclosed herein comprise a system and method for cementing the annulus between the wellbore and the casing that does not require pumping the cement at pressures that allow for leak off into low pressure zones. The system and method of the present invention identify when to stop pumping additional cement into the wellbore and do not require the use of expensive equipment including tools that must be retrieved from the well once the cementing operation is complete.

• Broadly stated, the system of the present invention comprises at least one interrogator that is operably associated with an actuatable device disposed within a wellbore and at least one detectable member disposed within a fluid. The detectable member is detectable by the interrogator when the detectable member comes in communicative proximity with the interrogator causing the interrogator to send a signal to actuate the actuatable device.

• The system of the present invention may be specifically used for closing a subterranean valve to terminate a reverse cementing operation. This system comprises at least one interrogator operably associated with the valve, an interface between a first fluid and a cement composition that is pumped through an annulus between a pipe string and a wellbore and at least one detectable member associated with the interface that is detectable by the interrogator when the detectable member comes in communicative proximity with the interrogator causing the interrogator to send a signal the close the valve.

• In one embodiment, the interrogator is an oscillator that produces a magnetic field and the detectable member is a resonant circuit. In another embodiment, the interrogator comprises a radio-frequency transmitter circuit that produces a radio-frequency signal and the detectable member is a radio-frequency modulator that modulates the radio-frequency signal and returns the modulated radio-frequency signal to the interrogator. In yet another embodiment of the present invention, the interrogator is a gamma ray detector and the detectable member is a gamma ray source.

• In one embodiment of the present invention, the interface is an interface fluid between the first fluid and the cement composition and the detectable member is disposed within the interface fluid. In another embodiment, the interface is a mud-cement interface and the detectable member is disposed proximate the mud-cement interface.

• Broadly stated, the method of the present invention involves the steps of operably associating at least one interrogator with the actuatable device, disposing at least one detectable member within a fluid, detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator and sending a signal from the interrogator to actuate the actuatable device.

• The method of the present invention may be specifically used for closing a subterranean valve to terminate a reverse cementing operation. In this case, the method involves the steps of operably associating at least one interrogator with the valve, disposing at least one detectable member within an interface between a first fluid and a cement composition, pumping the cement composition through an annulus between a pipe string and a wellbore, detecting the detectable member with the interrogator when the detectable member comes in communicative proximity with the interrogator and sending a signal from the interrogator to close the valve.

BRIEF DESCRIPTION OF THE DRAWING

• For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:

• FIG. 1 is a schematic illustration of an onshore oil or gas drilling rig operating a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention;

• FIG. 2 is schematic illustration of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention prior to actuating the valve;

• FIG. 3 is schematic illustration of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention following the actuation of the valve;

• FIG. 4 is a block diagram of one embodiment of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention;

• FIG. 5 is a block diagram of another embodiment of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention;

• FIG. 6 is a block diagram of another embodiment of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention;

• FIG. 7 is a flowchart detailing a method for actuating a subterranean valve to terminate a reverse cementing operation of the present invention;

• FIG. 8 is schematic illustration of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention prior to actuating the valve; and

• FIG. 9 is schematic illustration of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention following the actuation of the valve.

DETAILED DESCRIPTION OF THE INVENTION

• While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

• The present invention provides systems and methods for actuating a subterranean valve. Even though the systems and methods are described as being useful in actuating valves during reverse cementing, it should be understood by one skilled in the art that the systems and methods described herein are equally well-suited for actuating valves during other well operations and actuating downhole equipment other than valves.

• Referring to FIG. 1, an onshore oil or gas drilling rig operating a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention is schematically illustrated and generally designated 10.

  Rig

  12 is centered over a subterranean oil or

  gas formation

  14 located below the earth's

  surface

  16. A

  wellbore

  18 extends through the various earth

  strata including formation

  14.

  Wellbore

  18 is lined with a

  casing string

  20.

  Casing

  20 has a

  valve

  22 that is disposed proximate the far end of

  casing

  20.

  Valve

  22 is used to selectively permit and prevent the flow of fluids therethrough. For example, during a reverse cementing operation,

  valve

  22 remains open as drilling

  fluids

  24 is forced from

  annulus

  26 into the far end of

  casing

  20 when

  cement

  28 is pumped, via

  cement pump

  30, into the near end of

  annulus

  26. When the leading edge of

  cement

  28 reaches the far end of

  casing

  20,

  valve

  22 is closed to prevent

  cement

  28 from traveling within

  casing

  20. Thereafter,

  cement

  28 is allowed to set in

  annulus

  26 to form a hard, substantially impermeable mass which physically supports and positions casing 20 in

  wellbore

  18 and bonds casing 20 to the walls of

  wellbore

  18.

• Rig

  12 includes a

  work deck

  32 that supports a

  derrick

  34.

  Derrick

  34 supports a hoisting

  apparatus

  36 for raising and lowering pipe strings such as

  casing

  20.

  Pump

  30 on

  work deck

  32 is of conventional construction and is of the type capable of pumping a variety of fluids into the well.

  Pump

  30 includes a pressure measurement device that provides a pressure reading at the pump discharge.

• Referring now to FIG. 2, therein is depicted an enlarged view of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention that is schematically illustrated and generally designated 40. The far end of

  wellbore

  18 is shown with

  casing

  20 disposed therein.

  Valve

  22 is positioned within

  casing

  20 and is in the open position in FIG. 2.

  Valve

  22 may be of any suitable construction that is known in the art such as ball valves, sleeve valves or the like.

  Valve

  22 may be operated mechanically, electrically, electro-mechanically, hydraulically or by other suitable means.

• Valve

  22 has an

  actuator

  42 for operating

  valve

  22 between the open and closed positions. Coupled to

  actuator

  42 is a pair of

  interrogators

  44, 46.

  Interrogators

  44, 46 are used to send a signal to

  actuator

  42 when it is time to operate

  valve

  22. In the illustrated configuration,

  interrogators

  44, 46 are used to send a signal to

  actuator

  42 when it is time to operate

  valve

  22 from the open position to the closed position. It should be noted, however, by those skilled in the art the

  interrogators

  44, 46 could alternatively be used to operate

  valve

  22 from the closed position to the open position or could be used to operate other types of actuatable devices. In addition, even though FIG. 2 depicts two

  interrogators

  44, 46, it should become apparent to those skilled in the art that other numbers of interrogators, either a greater number or a lesser number, may be used to signal

  actuator

  42 to operate without departing from the principles of the present invention.

• Wellbore

  18 is filled with various fluids. As illustrated, the fluids include a

  drilling fluid

  48, an

  interface fluid

  50 including a plurality of

  detectable members

  52 and a

  hydraulic cement composition

  28. Drilling

  fluid

  48 may be any typical drilling fluid such as a water-based or oil-based drilling fluid. Importantly,

  drilling fluid

  48 is used to contain subsurface pressure. Accordingly,

  drilling fluid

  48 is weighted with various additives so that the hydrostatic pressure of

  drilling fluid

  48 is sufficient to contain subsurface pressure along the entire depth of

  wellbore

  18, thereby preventing blowouts.

• Interface fluid

  50 may be any suitably viscous fluid that is capable of maintaining substantial separation between

  drilling fluid

  48 and

  cement composition

  28. In addition,

  interface fluid

  50 is capable of containing and transporting the plurality of

  detectable members

  52 from the surface to the far end of

  wellbore

  18. For example, interface fluid may be a water-based or oil-based fluid.

• Cement composition

  28 may be any typical hydraulic cementitious material including those comprising calcium, aluminum, silicon, oxygen and/or sulfur which set and harden by reaction with water. Such hydraulic materials include Portland cements, pozzolana cements, gypsum cements, high aluminum content cements, silica cements and high alkalinity cements. Portland cements are generally preferred for use in accordance with the present invention. Portland cements of the types defined and described in API Specification for Materials and Testing for Well Cements,

  API Specification

  10, 5th Edition, dated Jul. 1, 1990 of the American Petroleum Institute are particularly suitable. Preferred API Portland cements include classes A, B, C, G and H, with API class H being the most preferred.

• The water used in forming

  cement composition

  28 can be from any source provided it does not contain an excess of compounds that adversely affect other components in

  cement composition

  28. Generally, water is present in a cement slurry composition of this invention in an amount in the range of from about 25% to about 100% by weight of hydraulic material therein and, more preferably, in an amount in the range of from about 30% to about 75% by weight of hydraulic material therein. In addition, various dispersing agents can also be utilized in

  cement composition

  28. The dispersing agent functions to facilitate the dispersal of the solids in the water, and allows the use of smaller amounts of water than is the case without the dispersing agent.

• The plurality of

  detectable members

  52 are suspended in

  interface layer

  50 and circulate with

  interface layer

  50 through

  annulus

  26 and into

  casing

  20 toward

  valve

  22 as

  cement composition

  28 is pumped into

  annulus

  26 at the surface. When one or more of the

  detectable members

  52 come within the communicative proximity of one or both of the

  interrogators

  44, 46,

  interrogators

  44, 46 identify the presence of

  detectable members

  52 and send a signal to

  actuator

  42 to close

  valve

  22.

• As

  detectable members

  52 are associated with

  interface fluid

  50, when

  detectable members

  52 are detected,

  interface fluid

  50 is near

  valve

  22. When

  interface fluid

  50 is near

  valve

  22,

  annulus

  26 is entirely filled with

  cement

  28. Thereafter,

  valve

  22 is closed which sends a pressure signal through the column of

  cement

  28 in

  annulus

  26 indicating that the cement pumps at the surface should be shut off. As best seen in FIG. 3, once

  detectable members

  52 are within the communicative proximity of

  interrogators

  44, 46,

  actuator

  42 closes

  valve

  22 which prevents

  cement

  28 from entering the portion of

  casing string

  20 above

  valve

  22.

• The detailed operation of various embodiments of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention will now be discussed. Referring to FIG. 4,

  interrogator

  60 and

  detectable member

  62, which is disposed within

  interface fluid

  50 between

  drilling fluid

  48 and

  cement

  28, are depicted in communicative proximity to one another.

  Interrogator

  60 is an electronic identification system that utilizes a magnetic field modulation system to monitor for the presence of

  detectable members

  62.

  Interrogator

  60 creates a

  magnetic field

  64 that becomes unbalanced or detuned when one or more

  detectable member

  62 pass through

  magnetic field

  64.

• Several different types of

  detectable members

  62 are suitable for use with

  interrogator

  60. In one type, the functional portion of

  detectable member

  60 consists of either an antenna and diode or an antenna and capacitors forming a resonant circuit. When placed in

  electromagnetic field

  64 generated by

  interrogator

  60, the antenna-diode marker generates harmonics of the interrogating frequency in the receiving antenna. The resonant circuit marker causes an increase in absorption of the transmitted signal so as to reduce the signal in a receiving coil. The detection of the harmonic or signal level change by

  interrogator

  60 indicates the presence of

  detectable member

  62.

• A second type of

  detectable member

  60 includes a first elongated element of high magnetic permeability ferromagnetic material disposed adjacent to at least a second element of ferromagnetic material having higher coercivity than the first element. When subjected to an interrogation frequency of electromagnetic radiation,

  detectable member

  62 causes harmonics of the interrogating frequency to be developed in the receiving coil of

  interrogator

  60. The detection of such harmonics by

  interrogator

  60 indicates the presence of

  detectable member

  62.

• When the

  detectable member

  62 is exposed to a dc magnetic field, the state of magnetization in the second element changes and, depending upon the design of

  detectable member

  62, either the amplitude of the harmonics chosen for detection is significantly reduced, or the amplitude of the even numbered harmonics is significantly changed. Either of these changes can be readily detected by

  interrogator

  60.

• In the illustrated embodiment,

  interrogator

  60 includes an

  oscillator

  66 that applies a sinusoidal current to two substantially identical electromagnetic

  field producing units

  68.

  Field producing units

  68 may be of similarly constructed conducting coils. The lines of the magnetic field produced by the coils are indicated by

  lines

  64.

• Any perturbation in the fields produced by

  detectable member

  62 is detected by a

  field detector unit

  70.

  Detector unit

  70 can be a coil in which the time varying fields induce a voltage. It should be noted that in the absence of a field perturbing object, such as

  detectable member

  62 when it is generally disposed in detectable proximity of the

  field detector unit

  70, the field is balanced.

• The signals produced by

  detector unit

  70 are amplified by an

  amplifier

  72. The output signal of

  amplifier

  72 is filtered by a

  filter

  74.

  Filter

  74 provides a means of eliminating any detected spurious signals at frequencies differing from the electromagnetic field frequency resulting from the interaction of

  detectable member

  62 in

  field

  64 and therefore provides a narrow ban signal of the desired frequency. The output of

  filter

  74 is amplified by an

  amplifier

  76 to provide a sufficient signal level to drive both

  phase comparator

  78 and

  amplitude comparator

  80.

• A portion of the output signal of

  amplifier

  76 is applied to the

  amplitude comparator circuit

  80. When the output signal of

  amplifier

  76 is between predetermined values, a positive logic signal is applied to

  detection logic circuits

  82. Another portion of the output of

  amplifier

  76 is applied to phase

  comparator circuit

  78. The phase of the amplifier output signal is compared with the phase of

  oscillator

  66. When the phases of the two signals differ by a predetermined value, a positive-logic signal is applied to

  detection logic circuits

  82. The simultaneous presence of the amplitude-related and the phase-related logic signals are necessary to activate the

  detection logic circuits

  82. Upon application of the proper positive logic signals to

  logic circuits

  82, an activate signal is applied to

  actuator

  42.

  Valve actuator

  42 triggers an actuation event such as the closing of

  valve

  22.

• Referring next to FIG. 5, another embodiment a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention is depicted. An

  interrogator

  90 and a

  detectable member

  92, which is disposed within

  interface fluid

  50 between

  drilling fluid

  48 and

  cement

  28, are positioned within communicative proximity of one another. Together,

  interrogator

  90 and

  detectable member

  92 may, for example, form a radio-frequency identification (RFID) system.

  Interrogator

  90 comprises a

  power source

  94, an interrogating

  signal generator

  96 with a sending transducer or

  antenna

  98. In addition,

  interrogator

  90 also comprises an amplifier and

  demodulator

  100 operably connected to a signal receiving transducer or an

  antenna

  102. In the illustrated embodiment, the interrogating

  signal

  104 and the

  response signal

  106 are typically radio-frequency (rf) signals produced by an rf transmitter circuit.

• Detectable member

  92 comprises a signal receiving and reflecting

  antenna

  108 and a

  reflector modulator

  110 for modulating interrogating

  signal

  104 received by the

  antenna

  108 as well as for reflecting the modulated signal,

  response signal

  106, from

  antenna

  108. As can be seen from FIG. 5, the

  power source

  94 powers interrogating

  signal generator

  96 to send interrogating signal 104 from

  antenna

  98. Preferably,

  power source

  94 is four AA batteries. Interrogating

  signal

  104 from

  antenna

  98 passes through the fluid medium and is received by

  antenna

  108 at

  detectable member

  92.

  Modulator

  110 modulates the signal in accordance with information desired and reflects the amplitude modulated signal,

  response signal

  106, from

  antenna

  108 to

  antenna

  102.

  Antenna

  102 send the signal to amplifier and

  demodulator

  100 which processes the signal to determine whether the response is from a

  detectable member

  92. Upon receipt of the proper response signal, amplifier and

  demodulator

  100 sends an activate signal to

  valve actuator

  42.

  Valve actuator

  42 triggers an actuation event such as the closing of

  valve

  22.

• It should be noted that interrogating

  signal

  104 generated by

  interrogator

  90 need not be a continuous wave or constant in amplitude and/or frequency. It may be appropriate in some applications to generate an interrogating

  signal

  104 that is intermittent. This might be done for various reasons such as conserving power. Many combinations and variations are possible as will be readily recognizable to those skilled in the art.

• Referring now to FIG. 6, another embodiment a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention is depicted. An

  interrogator

  120 and a

  detectable member

  122 are shown in communicative proximity to one another.

  Interrogator

  120 is a gamma ray detecting system that detects

  gamma rays

  124 originating close to

  interrogator

  120 from

  detectable member

  122 that is a radioactive source, which is disposed within

  interface fluid

  50 between

  drilling fluid

  48 and

  cement

  28.

  Detectable member

  122 emits

  gamma rays

  124 that travel only a short distance before being scattered or absorbed.

• A variety of gamma-emitting tracer isotopes are suitable for use within

  detectable member

  122, including but not limited to Gold¹⁹⁸, Xenon¹³³, Iodine¹³¹, Rubidium⁸⁶, Chromium⁵¹, Iron59, Antimony¹²⁴, Stontium⁸⁵, Cobalt⁵⁸, Iridium¹⁹², Scandium⁴⁶, Zinc⁶⁵, Siler¹¹⁰, Cobalt⁵⁷, Cobalt⁶⁰ and Krypton⁸⁵. During the cementing treatment,

  detectable member

  122 regularly emits

  gamma rays

  124, which move through the subterranean system in a random direction for a distance of perhaps one meter, and in the process are scattered and/or absorbed by the subterranean formation and steel tubular elements such as

  casing

  20. Since

  gamma rays

  124 from

  detectable member

  122 travel only a short distance before being absorbed, the

  gamma rays

  124 that impinge upon

  interrogator

  120 will have originated from a location close to

  interrogator

  120. In this manner,

  interrogator

  120 is able to detect when

  cement

  28 has progressed to the far end of

  wellbore

  18

  proximate valve

  22. Once detection occurs,

  valve

  22 may be closed and the pumping of

  additional cement

  28 is stopped before the interior of casing 20 is cemented.

• Interrogator

  120 may be a conventional gamma detector comprises, for example, a thallium activated

  sodium iodide crystal

  126 coupled to a

  low noise photomultiplier

  128 having appropriate electronics associated therewith all of which is encased in lead shielding. Upon detection of the proper

  gamma ray signal

  124, an activation signal is sent from

  photomultiplier

  128 to

  valve actuator

  42 such that

  valve

  22 may be closed.

• Referring now to FIG. 7, a flowchart outlining the method for actuating a subterranean valve to terminate a reverse cementing operation of the present invention is depicted. At

  block

  130, the valve equipped with the interrogator and valve actuator is lowered into the wellbore. The valve can be lowered with the casing string as an attachment to the casing string or, the valve could alternatively be lowered into the well after the casing string has been put into place.

• At

  block

  132, detectable members are placed in the interface fluid and the interface fluid is pumped into the annulus. At

  block

  134, cement is pumped into the annulus. While cement is continuously pumped into the annulus, at

  decision

  136, the interrogator is attempting to detect whether the detectable members are proximate the valve. As long as no detectable members are detected, the pumping of additional cement into the annulus continues. When the interrogator detects the detectable member at

  block

  138, the interrogator sends a signal to the valve actuator at

  block

  140.

• At

  block

  142, the actuator closes the valve such that no additional fluid may flow into the casing. This creates a pressure signal that is detected at the hydraulic pump at

  block

  144. The cement pumping is discontinued at

  block

  146. The cement in the annulus is allowed to set and form a hard, substantially impermeable mass which physically supports and positions the casing in the wellbore and bonds the casing to the walls of the wellbore in

  block

  148.

• Referring now to FIG. 8, therein is depicted an enlarged view of a system for actuating a subterranean valve to terminate a reverse cementing operation of the present invention that is schematically illustrated and generally designated 150. The far end of

  wellbore

  18 is shown with

  casing

  20 disposed therein.

  Valve

  22 is positioned within

  casing

  20 and is in the open positioned in FIG. 8.

  Valve

  22 has an

  actuator

  42 for operating

  valve

  22 between the open and closed positions. Coupled to

  actuator

  42 is a pair of

  interrogators

  44, 46.

  Interrogators

  44, 46 are used to send a signal to

  actuator

  42 when it is time to operate

  valve

  22. In the illustrated configuration,

  interrogators

  44, 46 are used to send a signal to

  actuator

  42 when it is time to operate

  valve

  22 from the open position to the closed position.

• In the illustrated embodiment, wellbore 18 is filled with two fluids, namely,

  drilling fluid

  48 and

  hydraulic cement composition

  28 which form a mud-

  cement interface

  152 therebetween. A plurality of

  detectable members

  52 are disposed proximate the mud-

  cement interface

  152 such that

  detectable members

  52 circulate through

  annulus

  26 and into

  casing

  20 toward

  valve

  22 as

  cement composition

  28 is pumped into

  annulus

  26 at the surface. When one or more of the

  detectable members

  52 come within the communicative proximity of one or both of the

  interrogators

  44, 46,

  interrogators

  44, 46 identify the presence of

  detectable members

  52 and send a signal to

  actuator

  42 to close

  valve

  22.

• As

  detectable members

  52 are associated with mud-

  cement interface

  152, when

  detectable members

  52 are detected, mud-

  cement interface

  152 is near

  valve

  22. When mud-

  cement interface

  152 is near

  valve

  22,

  annulus

  26 is entirely filled with

  cement

  28. Thereafter,

  valve

  22 is closed which sends a pressure signal through the column of

  cement

  28 in

  annulus

  26 indicating that the cement pumps at the surface should be shut off. As best seen in FIG. 9, once

  detectable members

  52 are within the communicative proximity of

  interrogators

  44, 46,

  actuator

  42 closes

  valve

  22 which prevents

  cement

  28 from entering the portion of

  casing string

  20 above

  valve

  22.

• While this invention has been described with a reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.