Abstract: The application is directed to a power system that may be provided in a portable form and operationally configured for use at a work site as a single source of electric power, hydraulic power and pneumatic power for work site operations. In regard to hydraulic fracturing stimulation of a wellbore, the power system is operationally configured as the source of hydraulic power for transportable pumping units of a fracturing operation and for hydraulic power tools, as the source of pneumatic power for pneumatic power tools and as the source of electric power for electric power tools and electronic equipment at a well site.

Abstract: Downhole tools, including downhole valves, may actuate via a pressure differential created across a shifting element having one or more pressure surfaces isolated from fluid, and fluid pressure, flowing through the interior flowpath. Embodiment downhole tools of the present disclosure may actuate in response to, among other signals, fluid pressure in the interior flowpath of the tool and fluid pressure communicated to a pressure surface of the shifting sleeve from the exterior of the tool. Certain embodiments may also have an outlet connector whereby fluid pressure from the downhole tool may be communicated to its exterior. Isolation of the shifting element from the interior flowpath may be accomplished using a frangible, shiftable, degradable or other members which may be moved from a closed state to an open state in response to fluid conditions in the interior flowpath.

Abstract: A downhole control system can include a pair of drive lines passing through a wellbore member such as a tubing hanger, and a plurality of hydraulic switches, each in communication with the drive lines. Each hydraulic switch can have a unique pressure band, wherein the switch only responds when the pressure in the drive lines is within the unique pressure band. Once the pressure in the drive lines is within the pressure band, the switch can open or close in response to a pressure differential in the drive lines.

Abstract: A method, apparatus and composition are described for safe energy delivery down hole resulting in increased recovery of subterranean hydrocarbons. The method utilizes, for example, the reaction of non-alkane fuels and selective oxidizers which are non-selective toward alkane chemical compounds. The method further utilizes an acid solution reaction with aforementioned reaction for elimination of any insoluble products of reaction permitting flow within formation strata. The energy released in the subterranean reaction is utilized to heat the production tubing, the wellbore, the formation or the formation hydrocarbons thereby lowering fluid viscosity and permitting greater flow especially for heavy oils, asphaltene deposits and/or paraffin deposits.

Abstract: A downhole activation assembly for a wellsite is provided. The wellsite has a downhole tool deployable into a wellbore. The activation assembly includes a ball, a housing, an indexing assembly, and a sleeve valve. The housing is operatively connectable to the downhole tool, and has a housing passage for flow of fluid therethrough. The indexing assembly is positionable in the housing, includes a multiple position indexer and an indexing tube, and is operatively connectable to the downhole tool. The sleeve valve includes a fixed sleeve and a movable sleeve positionable in the housing passage of the housing and defines a ball passage therethrough. The sleeve valve has a valve seat defined therein to receive the ball such that the flow of the fluid is selectively restricted through the ball passage. The movable sleeve is engagable with the indexing tube to selectively shift the indexer between multiple positions whereby the downhole tool is selectively activatable.

Abstract: In one aspect, a system includes a tool, a hanger connected to the tool, and a plurality of tubulars connected to the hanger and adapted to be positioned within a wellbore. The tool, hanger, and tubulars are rotatable in response to at least the application of torsion to the tool, and without transferring torque to the connection between the tool and the hanger. In another aspect, a method includes positioning a tubular string within a wellbore, connecting a hanger to the tubular string, and applying torsion to the tubular string to rotate the tubular string. To apply torsion to rotate, a tool is connected to the hanger, and torsion is applied to the tool without transferring torque to the connection between the tool and the hanger. In another aspect, there is provided an apparatus for rotating a tubular string in a preexisting structure, such as a wellbore.

Abstract: A wellbore machining device is proposed for machining a tubular component of a wellbore. The device includes a control unit at the surface level of the wellbore and a down-hole tool unit connected to the control unit through a wire line. The tool unit includes an elongated guide member, a tool member movably supported on the guide member with respect to at least three axes of motion and a plurality of actuators controlled by the control unit and adapted to move the tool member with respect to the axes of motion. The tool unit further includes two anchor members each mounted to an axial end of the guide member and adapted to releasably clamp the tool unit to the tubular component. The control unit and the tool unit form a computer numerical control device (CNC device) wherein the actuators are electric servo motors controlling an actual position of the tool member with respect to a path and/or a sequence of desired position defined by the control unit.

Abstract: A method and apparatus for setting a subsurface device in a wellbore is disclosed. A downhole power unit comprises a power rod and a drive shaft. The power rod comprises a hollow interior. The drive shaft is located within the hollow interior, and the power rod is operable to selectively engage a subsurface device to be positioned downhole.

Abstract: A stage tool apparatus is described. In several exemplary embodiments, the stage tool apparatus is part of tubular string or casing positioned within a preexisting structure such as, for example, a wellbore.

Abstract: A well drilling tool has a tubular member connected into a casing string that serves as a drill string. A load shoulder is located within the bore of the tubular member. The load shoulder has a torque transferring portion that extends from a lower terminus to an upper terminus. The load shoulder has an axial force transferring portion that faces upward. A bottom hole assembly is lowered through the casing string and lands on the load shoulder. The bottom hole assembly has a mating profile to the load shoulder so that it will be supported by the load shoulder and will receive torque transferred from the load shoulder.

Abstract: This invention relates to a downhole hydraulic pump for hydrocarbon wells that is installed and operated using coiled tubing. The downhole hydraulic pump is driven by a hydraulic power system positioned at the surface and connected through a closed loop system using multiple channels of the coiled tubing. The coiled tubing is formed of a combination of channels including strength component such as steel and having one channel that is at least lined with a non-metallic corrosion resistant surface where clean hydraulic fluid is carried from the hydraulic power system to the downhole hydraulic pump through the non-metallic corrosion resistant channel so to be less likely to pick up manufacturing and environmental particulates and corrosion by-products within the channel carrying the hydraulic fluid to the downhole hydraulic pump. The non-metallic corrosion resistant lined channel may comprise plastic pipe.

Abstract: A hydraulically balanced multiple drop well completion has a plurality of hydraulic control lines each of which communicates hydraulic inputs and a plurality of hydraulically operated tools numbering greater than or equal to the number of hydraulic control lines. Each of the hydraulic control lines is connected to at least one of the hydraulically operated tools to communicate hydraulic inputs to actuate the hydraulically operated tools. Each of the hydraulically operated tools discharges hydraulic fluid to one of the hydraulic control lines other than the hydraulic control line from which it receives the controlling hydraulic input.

Abstract: A casing mandrel for an independent screwed wellhead includes a seal bore for receiving a fixed-point packoff connected to a high-pressure mandrel of a pressure isolation tool, and a pin thread adapted for engagement with a box thread of a tubing head supported by the casing mandrel.

Abstract: A stage tool apparatus is described. In several exemplary embodiments, the stage tool apparatus is part of tubular string or casing positioned within a preexisting structure such as, for example, a wellbore.

Abstract: This invention relates to a downhole hydraulic pump for hydrocarbon wells that is installed and operated using coiled tubing. The downhole hydraulic pump is driven by a hydraulic power system positioned at the surface and connected through a closed loop system using multiple channels of the coiled tubing. The coiled tubing is formed of a combination of channels including strength component such as steel and having one channel that is at least lined with a non-metallic corrosion resistant surface where clean hydraulic fluid is carried from the hydraulic power system to the downhole hydraulic pump through the non-metallic corrosion resistant channel so to be less likely to pick up manufacturing and environmental particulates and corrosion by-products within the channel carrying the hydraulic fluid to the downhole hydraulic pump. The non-metallic corrosion resistant lined channel may comprise plastic pipe.

Abstract: An embodiment of a valve that is operable from one position to another position upon relief of an applied pressure includes a housing having a bore; a valve member disposed with the housing, wherein the valve member is actuated to one position in response to a certain applied pressure and actuates toward another position upon relief of the certain applied pressure; and a relief system relieving the pressure applied to the valve member when the applied pressure falls below a selected pressure level.

Abstract: A casing mandrel for an independent screwed wellhead includes a seal bore for receiving a fixed-point packoff connected to a high-pressure mandrel of a pressure isolation tool, and a pin thread adapted for engagement with a box thread of a tubing head supported by the casing mandrel.

Abstract: A selectively communicatable hydraulic nipple is provided which includes an upper and lower communications component adapted to communicate with tools landed inside the hydraulic nipple. Each communications component communicates with a control line used by the hydraulic nipple. An operator is allowed to selectively communicate with tools landed inside the nipple via the upper and lower communications components via the nipple control line. As a result, should the TRSCSSV control line loose integrity, the operator has the option of utilizing the nipple control line to continue oil and gas production without the need for well modifications. Alternatively, an operator could land a chemical injection tool, with an injection string suspended therefrom, in the nipple and inject chemicals into the well via the nipple control line.

Abstract: An acoustic telemetry system includes a piezoelectric stack at least partially disposed within a segment of pipe, and electrical circuitry for controlling the piezoelectric stack. In response to a signal from the electrical circuitry, the piezoelectric stack generates a plurality of acoustic signals for transmission through the pipe at different frequencies spanning multiple regions of a frequency response for the pipe.

Abstract: A control line clearing apparatus has a separation sleeve that positions into a downhole element adjacent the element's control port to which a blocked control line connects. The sleeve separates fluid communication from the control port with the annulus between the sleeve and the downhole element, while still allowing effluents in the well tubing to pass through the interior of the sleeve. A feed line is then lowered into the sleeve, and an automatic coupling on the end of the feed line couples to a coupling member inside the sleeve. Once connected, solvent fed through the feed line communicates with the downhole elements control port via a cross-port in the sleeve. In this way, the solvent can act against the other side of the control line blockage.

Abstract: A communication system for a casing while drilling system is provided. The casing while drilling system is adapted to advance a bottom hole assembly into a subsurface formation via a casing. The communication system comprises a high frequency modulator and a transducer. The modulator is positioned in the bottom hole assembly and adapted to generate a mud pulse by selectively restrict mud flow passing therethrough. The transducer is adapted to detect the mud pulse generated by the modulator.

Abstract: A technique provides a system and method to verify attachment of a fishing tool with a downhole well tool. The fishing tool comprises a latching mechanism that latches onto the well tool to be retrieved. The fishing tool also comprises a detection device to verify connection of the latching mechanism. The detection device provides a signal uphole to verify attachment to the well tool.

Abstract: A method of drilling a well and installing a liner includes assembling concentric inner and outer strings of tubulars. A drill bit is located at the lower end of the inner string and a liner with a liner hanger makes up part of the outer string. The inner and outer strings may be rotated in unison to drill the well. At a selected depth, the operator sets the liner hanger and retrieves the inner string. The operator lowers a packer and a cement retainer on a string of conduit. The packer engages the liner hanger and the cement retainer is conveyed to the lower end of the liner. The cement retainer prevents cement in the outer annulus from flowing back up the string of conduit. The operator manipulates the conduit to set the packer.

Abstract: A liner drilling system employs a bottom hole assembly that may be retrieved before reaching the total liner depth. The system includes an outer string made up of a liner and a profile nipple. An inner string including a running tool, drill pipe, and a drill lock tool are lowered into the outer string and rotationally and axially locked to the outer string. Drilling may be performed by rotating the inner string, which also rotates the outer string. The operator may retrieve the inner string by pulling the inner string and the liner upward until the upper end of the liner is located at the drilling rig floor. While supporting the liner at the drilling rig floor, the operator retrieves the inner string, then re-runs it back into the outer string.

Abstract: A hydraulic actuator connected between a downhole tool and a hydraulic control line for operating the downhole tool through an actuation sequence includes a valve shuttle section having an inlet port in connection with the hydraulic control line, a first function port and a second function port, and a shuttle moveable between positions providing fluid communication between the inlet port and the first function port and the inlet port and the second function port; and a pilot assembly in fluid connection with the hydraulic control line and in operational connection with the shuttle, the pilot assembly movable in response to an actuation cycle comprising applying pressure from the hydraulic control line and bleeding the pressure off.

Abstract: Casing valves for selective well stimulation and control. A well system includes at least one valve interconnected in a casing string operable via at least one line external to the casing string to selectively control fluid flow between an exterior and interior of the casing string, and the casing string, valve and line being cemented in a wellbore. A method of selectively stimulating a subterranean formation includes: positioning a casing string in a wellbore, the casing string including spaced apart valves operable via a line to selectively control fluid flow between an interior and exterior of the casing string; and for each of multiple intervals of the formation in sequence, stimulating the interval by opening a corresponding one of the valves, closing the remainder of the valves, and flowing a stimulation fluid from the casing string into the interval.

Abstract: A safety valve (100) replaces an existing safety valve (102) in order to isolate a production zone from a tubing string when closed. Preferably the safety valve (100) includes a flow interruption device (106) displaced by an operating conduit extending from a surface location to the safety valve (100) through the inside of the production tubing. A by-pass conduit (150) allows communication from a surface location to the production zone through the safety valve (100) without affecting the operation of the safety valve (100).

Abstract: A continuous sucker rod preferably comprising fiberglass or composite material for use in an well is described herein. The continuous sucker rod may be connected at one end to a pump drive, via a polished rod, and at a second end to a downhole pump, via sinker bars or other weights. The continuous sucker rod preferably has at least two end fittings, one at each end of the continuous sucker rod. The end fittings, each having two ends and each being attached, at one end, to a respective end of the continuous sucker rod. The end fittings are preferably configured to enable connection to the polished rod and sinker bars respectively. The end fittings are connected to the continuous sucker rod so as to form wedges which enhance the connectability of the end fitting to the rod, and further, the wedge or wedges approach the rod asymptotically so as to avoid any abrupt discontinuities in the wedge or wedges thus substantially eliminating stress concentration areas and potential failure areas in the rod.

Abstract: Apparatuses and methods to inject chemical stimulants (284) to a production zone (102, 202) through a string of production tubing (110, 210) around a downhole obstruction are disclosed. The apparatuses and methods include deploying an anchor seal assembly (200) to a landing profile (120, 220) located within a string of production tubing (110, 210). The anchor seal assembly (200) is in communication with a surface station through an injection conduit (260, 264) and includes a bypass pathway (262) to inject various fluids to a zone below.

Abstract: An apparatus and methods of electrically controlling downhole well interval inflow and/or injection. The downhole controllable well section having a communications and control module, a sensor, an electrically controllable valve and an induction choke. The electrically controllable valve is adapted to regulate flow between an exterior of the tubing and an interior of the tubing. Power and signal transmission between surface and downhole is carried out via the tubing and/or the casing. When there are multiple downhole controllable well sections, flow inhibitors separate the well sections.

Abstract: A system and method of communicating among devices via a piping structure using at least one induction choke about the piping structure to route a time-varying current carrying communication signals between the devices. A communications system comprises a piping structure, a first communication device, a second communication device, and an induction choke. The piping structure comprises a first location, a second location, and an electrically conductive portion extending between the first and second locations. The first and second locations are distally spaced along the piping structure. The first and second communication devices are each electrically connected to the electrically conductive portion of the piping structure along the first location and second location, respectively, and each is adapted to send and receive communication signals via time-varying current.

Abstract: A petroleum well for producing petroleum products that incorporates a system adapted to controllably route communications and/or electrical power having a time-varying current through a piping structure in the well, and methods of producing petroleum products use such a well, are provided by the present invention. The system comprises a first induction choke, a second induction choke, and a controllable switch. The first induction choke is located about a portion of a first branch of the piping structure. The second induction choke is located about a portion of a second branch of the piping structure. The controllable switch having two switch terminals. A first of the switch terminals I is electrically connected to the piping structure on a junction side of the induction chokes. The first and second branches of the piping structure intersect on the junction side of the induction chokes.

Abstract: A petroleum well having a communication system and a hydraulic system is provided. The petroleum well includes a borehole and a piping structure positioned within the borehole. The communication system supplies a time varying electric current downhole along the piping structure. The hydraulic system, which is positioned downhole proximate the piping structure, receives the time varying current to operate an electric motor. The motor drives a pump which pressurizes hydraulic fluid to selectively drive an actuator. The actuator is operably connected to a downhole device, such as a shutoff valve, and operates the downhole device as the actuator is driven by the pressurized hydraulic fluid.

Abstract: The present invention is a method of transmitting one or more acoustic signals in a drill string using PSK, ASK, FSK or MSFK. The method includes determining one or more stopbands and one or more passbands by testing or modeling the drill string. Two modulating frequencies are selected that are equidistant about a carrier frequency, and which are located within at least one passband. Data representative of downhole measurements or calculations are converted to signals to be transmitted at the modulating frequencies.

Abstract: A technique for facilitating the use of a variety of completion elements in a wellbore environment. The technique utilizes an insertion guide disposed within an open-hole section of a wellbore. The insertion guide may be radially expanded towards the surrounding formation to remove excess annular space. The expansion of the insertion guide further allows the use of a completion element having a greater diameter than would otherwise be afforded.

Abstract: A safety system controls the activation of one or more downhole tools by providing selective transmission of an activation signal or an energy stream. In a preferred embodiment, transmission of the activation signal or the energy stream is allowed after the tool has passed below a known pre-determined depth. A preferred safety system includes a first device in fixed relationship with the downhole tool and a second device fixed at the stationary location. The first device permits, after reaching the pre-determined depth, either (a) an initiation signal to reach an initiation device associated with a downhole tool upon or (b) the energy stream to reach a downhole tool. The second device positively engages the first device to provide an indication that the specified depth has been reached.

Abstract: A system and method of communicating among devices via a piping structure using at least one induction choke about the piping structure to route a time-varying current carrying communication signals between the devices. A communications system comprises a piping structure, a first communication device, a second communication device, and an induction choke. The piping structure comprises a first location, a second location, and an electrically conductive portion extending between the first and second locations. The first and second locations are distally spaced along the piping structure. The first and second communication devices are each electrically connected to the electrically conductive portion of the piping structure along the first location and second location, respectively, and each is adapted to send and receive communication signals via time-varying current.

Abstract: An apparatus and method for pumping fluids in a wellbore. The apparatus includes a pipe string in the wellbore extending between a wellhead end and a production end, the pipe string defining an interior fluid path. A swivel device is connected into the pipe string so that an upper portion of the pipe string rotates relative to a lower portion thereof. A lower connector connects the lower portion with a stator of a rotary pump such that a fluid pumped by the pump is conducted through the interior fluid path of the pipe string. An upper connector connects the upper portion with a rotor of the rotary pump such that rotation of the upper portion rotates the rotor and thus pumps the fluid. The method includes rotatably supporting the upper portion in the wellbore at the wellhead end, connecting the lower portion with the stator, connecting the upper portion with the rotor, positioning the pump in the wellbore and rotating the upper portion in order to rotate the rotor to pump the fluid.

Abstract: A method is disclosed for installing a tubular member, having an upper end and a closed lower end, axially into and through an over-pressured region of the earth by using a mandrel to drive the tubular member from near the bottom, which results in a significant section of the tubular member being pulled through the over-pressured region. In another embodiment, a filler material is inserted into at least a portion of the tubular member, and the tubular member is driven from the upper end, with the filler material assisting the progression of the tubular member through the over-pressured region.

Abstract: Pipe used in drilling and/or completing wells is stored in long rectilinear segments or strings in the space adjacent a drilling rig being used to construct a well. The pipe is introduced into the well, or extracted from the well, in long segments made up of multiple individual pipe sections. In one embodiment, long rectilinear segments of pipe are bent into a curve that extends from the rig to the space surrounding the rig, where the pipe re-assumes its rectilinear shape. The curve radius is greater than the pipe's yielding bending radius. On a water-based rig, the pipe is received in the water surrounding the rig where it may be stored, tested, inspected, reassembled, treated, and/or otherwise processed. The pipe may be received within a long pipe storage sleeve that is buoyed laterally at or below the water surface or it may be secured to a guy line anchored between the rig and the water bottom.

Abstract: A method is disclosed for installing a tubular member, having an upper end and a closed lower end, axially into and through an over-pressured region of the earth by using a mandrel to drive the tubular member from near the bottom, which results in a significant section of the tubular member being pulled through the over-pressured region. In another embodiment, a filler material is inserted into at least a portion of the tubular member, and the tubular member is driven from the upper end, with the filler material assisting the progression of the tubular member through the over-pressured region.

Abstract: A new cementing system has been developed which includes, in certain embodiments, a plug container with a flow diverter for diverting a portion of flowing fluid away from plugs in the plug container; a plug set system with internal sleeves or dart receivers with shearable parts for shearing to selectively release plugs--all in certain embodiments made of non-metal material and/or plastic; and a swivel equalizer with internal valving to isolate a plug set (or any other item) from torque and to relieve pressure below the swivel equalizer.

Abstract: A crooked, slanted, cased wellbore extends downhole to a pay zone which is produced by a rod actuated downhole pump that lifts fluid from the bottom of the wellbore up through a tubing string to a wellhead. The pump is seated in a pump cavity, and the tubing string is tensioned at opposed ends while it is rotated. The upper end of the tubing string is attached to a fluid conveying swivel and a tubing rotator. A tubing anchor having a fluid conveying rotatable mandrel is attached adjacent to and forms part of the lower end of the tubing string by which the lower end of the tubing string is rotatably tensioned and releasably affixed to the casing in proximity to the lower end of the wellbore. A plurality of radially active slips are actuated in response to manipulation of the tubing string to extend the slips into engagement with the casing wall and to retract the slips in order to remove the tubing string from the borehole.

Abstract: There is disclosed a tool for enhancing the impact of a jar delivered to an object stuck in a well bore during both upward and downward jars to the stuck object. The tool includes a first tubular member having an lower end connectible to the tubular member of the jar on which the hammer is mounted and a second tubular member connectible to a well pipe string above it and arranged for reciprocation with respect to the first member to form an annular space between them. The space is divided into upper and lower chambers by means of seal rings disposed between the members and the spaces are filled with a compressible fluid which is compressed as the second tubular member is moved in either upward or downward directions.

Abstract: A cased wellbore extends downhole to a pay zone which is produced by a rod actuated downhole pump that lifts fluid from the bottom of the wellbore up through a tubing string to a wellhead. The pump is seated in a pump cavity, and the tubing string is tensioned and is rotated. The upper end of the tubing string is attached to a fluid conveying swivel and a tubing rotator. A combination tubing anchor having a fluid conveying rotatable mandrel is attached adjacent to and forms part of the lower end of the tubing string by which the lower end of the tubing string is rotatably and releasably affixed to the casing in proximity to the lower end of the wellbore. A plurality of radially active slips are actuated in response to manipulation of the tubing string to extend the slips into engagement with the casing wall and to retract the slips in order to remove the tubing string from the borehole.

Abstract: A new pump or injection apparatus is adapted to be connected between a pipe and a valve and is adapted to either pump well fluids from a wellbore or inject fluids into a formation traversed by the wellbore. The valve includes a full bore passage and a surrounding inlet flow channel.

Abstract: The present invention provides a preperforated casing for a well bore and a method of installing a preperforated casing in a well bore. The inventive casing comprises (a) a conduit having a plurality of apertures extending through the wall thereof and (b) a liner fixed adjacent at least a portion of the interior surface of the conduit such that the liner is positioned adjacent the apertures and is operable for preventing fluid flow through the apertures. The liner is removable from the conduit by drilling. Additionally, the liner comprises a material which, upon drilling, will break up into pieces which can be readily circulated out of the well. The inventive method comprises the steps of running the inventive casing into a well bore and then drilling the liner such that the liner is broken up into pieces and the above-mentioned apertures are open for fluid flow.

Abstract: A cased wellbore extends downhole to a pay zone which is produced by a rod actuated downhole pump that lifts fluid from the bottom of the wellbore up through a tubing string to a wellhead. The pump is seated in a pump cavity. The tubing string is tensioned and is rotated. The upper end of the tubing string is attached to a fluid conveying swivel means and a tubing rotator. A combination tubing anchor and fluid conveying swivel is attached adjacent the lower end of the tubing string by which the lower end of the tubing string is rotatably and releasably affixed to the casing in proximity to the lower end of the wellbore. The lower swivel is located adjacent the anchor and enables the tubing string to rotate respective to the anchor while conveying fluid through the rotating tensioned production tubing string.

Abstract: An apparatus 10 for removing underground contaminants from a contaminated subsurface area 16 is provided. The apparatus 10 includes a wellbore 12 aligned in the contaminated subsurface area for releasing predetermined substances into selected areas of the contaminated subsurface area so that the substances and contaminates are intermixed and for recovering the intermixture of substances and contaminates from selected areas of the contaminated subsurface area. A driving apparatus 83 is provided for rotating and sliding an inner housing 68 of the wellbore 12 along first and second predetermined paths respectively. An injection system 22 injects the predetermined substances into the wellbore 12 and recovery system 26 applies pressure to the wellbore so that the intermixture of substances and contaminants can be extracted from the contaminated area. The intermixture of substances and contaminates are then collected and stored for subsequent removal in a vacuum tank 28.

Abstract: The invention is an apparatus for measuring pressure, which comprises a pressure communicating device (3) for location at a point (4) at which pressure is to be measured, a primary tube (1) containing a fluid for linking the pressure communicating device (3) to a control point (9) where the pressure information is required, a sealing device for sealing the primary tube (1) so as to form a closed system when the pressure communicating device (3) is closed, a pressure control device (6) for changing the pressure of the fluid within the primary tube (1), a volume measuring device (8) for measuring changes in the volume of the fluid within the primary tube (1) as the pressure of the fluid is varied, a pressure measuring device (7) for measuring the pressure of the fluid at some point within the fluid, and device remote from the control point (9), and a transmitter device for transmitting pressure information from the pressure measuring device to the control point (9).