Abstract: A clean out sub for use in a drill string having a tool body with a cavity for passage of drilling fluid and annular fluid circulation ports extending through the tool body, a valve spool is positioned within the tool body cavity having a reduced diameter orifice, a compression spring is located within the tool body cavity adjacent the valve spool, wherein a drop in fluid pressure created by the orifice imparts a downhole force on the valve spool and at a predetermined force overcomes a set resistive force of the compression spring thereby moving the valve spool to open the annular fluid circulation ports.

Abstract: A hydraulic fluid control system for controlling pressure fluid supplied to consumers (2, 3, 4) of a rock drilling machine, a regulating valve (6, 7, 8) for each for each consumer and fluid conduits between the regulating valves and the consumers, an electronically controlled auxiliary control unit (11) having an electrically controlled auxiliary valve (14) for connection to a fluid conduit, a sensor for sensing fluid parameter values and sending sensor signals to the auxiliary control unit as sensor input signal actual values, micro-controller (12) having at least one parameter sensor input signal entry (S1-S5, I1-I5) for receiving the sensor input signal actual values and a control signal exit (V1-V6) for signal control of an auxiliary valve, the processor (12) is being arranged to compare the actual and predetermined values and to emit control signals to an auxiliary valve in response to the comparison to adjust fluid flow.

Abstract: The present invention is directed to an automatic drill fluid measurement apparatus. More specifically, the present invention is directed to an apparatus which may automatically measure a weight or volume of a quantity of drill fluid and provide real-time feedback information regarding the drill fluid to a well operator. The automatic drill fluid measurement apparatus may further comprise a variety of sensors and other devices that are used in conjunction with a microprocessor to obtain useful information regarding drill fluid, such as mass flow meters, volume sensors and timers. Together, the apparatus, sensors and microprocessor may work together to control the opening and closing of valves of the measurement apparatus.

Abstract: Diverting flow in a drilling fluid circulation system to regulate drilling fluid pressure. A pump of a drilling fluid pressure regulation system for a well bore can discharge drilling fluid through discharge piping at flow rate. A pressure control device has an inlet connected to the discharge piping and an outlet connected to bypass piping. A processor connected to the pump and the pressure control device can adjust the pressure control device to modify a pressure of the drilling fluid by at least partially opening the pressure control device and releasing drilling fluid into the bypass piping at a selected flow rate. The processor can modify the drilling fluid flow rate in the discharge piping based on the pressure represented by the pressure measurement signals and the selected flow rate in the bypass piping such that the target pressure parameter of the drilling fluid in the discharge piping is satisfied.

Abstract: A closed loop drilling fluids circulation system includes a first drilling fluid circulation system disposed at a first subterranean drill site. The first drilling fluid circulation system includes a supply tank for holding clean drilling fluid and a solids control device configured to separate solids from used drilling fluid. In addition, the system includes a central processing facility disposed at a location remote from the first drill site and configured to receive used drilling fluid from the solids control device and supply clean drilling fluid to the supply tank.

Abstract: A downhole tool includes a downlinking system deployed in a downhole tool body having an internal through bore. The downlinking system includes a differential pressure transducer configured to measured a pressure difference between drilling fluid in the internal through bore and drilling fluid external to the tool (in the borehole annulus). The differential transducer is electrically connected with an electronic controller (deployed substantially anywhere in the drill string) that is configured to receive and decode pressure waveforms.

Abstract: A method and system to aid and/or train well control personnel by measuring the actual hydraulic delay and pressure attenuation of operator choke changes during well control operations or simulations. This provides the choke operator with an anticipated drillpipe pressure as soon as the choke is adjusted, accounting for hydraulic delay, pressure attenuation and prior choke adjustments that are currently travelling through the wellbore as well as reflections of the transient pressure waves against the pumps and choke. The technique that is described utilizes only three inputs, and works without knowledge of or inputting data such as well depth, pipe and hole geometry, mud properties, temperature, water depth, land, offshore platform or floating (subsea BOP's) drilling rigs. Further, the system can detect and warn the operator of potential problems based on the results of the real time analysis.

Abstract: A drilling system includes a drill string extending through a BOP and a drilling fluid discharge coupling mounted to the BOP. In addition, the drilling system includes a drilling fluid control system configured to control a pressure or flow rate of a drilling fluid flowing through the discharge coupling. The drilling fluid control system includes a flow rate and pressure regulating device, a feedback controller system configured to operate the regulating device, and a first sensor configured to measure an actual pressure or flow rate of the drilling fluid flowing through the discharge coupling.

Abstract: A method of drilling a subterranean borehole comprising: a) pumping a drilling fluid down a drillstring (12), the drillstring (12) having a bit (14) at an end thereof, b) rotating the drillstring (12) about its longitudinal axis so that the bit forms a borehole (10) in the ground, the method further comprising the steps of: c) determining a desired drilling fluid flow rate range d) determining the desired upper and lower limits of the fluid pressure at the bottom of the wellbore (the BHP); e) determining the viscosity of drilling fluid which will maintain the BHP within the range set by the upper and lower BHP limits over the entire or the majority of the required drilling flow rate range; f) adjusting the composition of a drilling fluid to bring the drilling fluid to the viscosity calculated in step e above.

Abstract: A method of drilling a subsea wellbore includes drilling the subsea wellbore and, while drilling the subsea wellbore: measuring a flow rate of the drilling fluid injected into a tubular string; measuring a flow rate of returns; comparing the returns flow rate to the drilling fluid flow rate to detect a kick by a formation being drilled; and exerting backpressure on the returns using a first variable choke valve. The method further includes, in response to detecting the kick: closing a blowout preventer of a subsea pressure control assembly (PCA) against the tubular string; and diverting the flow of returns from the PCA, through a choke line having a second variable choke valve, and through the first variable choke valve.

Abstract: A method of selectively actuating a downhole tool, wherein the downhole tool includes a tubular body with an axial borehole therethrough and at least one component, includes increasing a flow rate of a circulating fluid in the axial borehole of the downhole tool to reach a specified circulating fluid pressure, detecting an increased circulating fluid pressure in the borehole of the tool with at least one sensor, actuating a motor to operate a pump, and sending a fluid to operate a sliding sleeve. The method further includes operating the sleeve disposed in the axial borehole to open an actuation chamber port in response to the increased circulating fluid pressure in the borehole of the tool, thereby filling an actuation chamber with the drilling fluid, and moving the at least one expandable component radially outward.

Abstract: A system and method for safely controlling a well being drilled or that has been drilled into a subterranean formation in which a conventional blow-out preventer operates to close the well bore to atmosphere upon the detection of a fluid influx event. Fluid pressures as well as fluid flow rates into and out of the well bore are measured and monitored to more accurately and confidently determine the fracture pressure and pore pressure of the formation and perform well control operations in response to a fluid influx event. During a suspected fluid influx event, one or more of the fluid flow and pressure measurements are used to confirm the fluid influx event and to safely regain well control by circulating the fluid influx out of the well through a choke line while maintaining the pressure inside the well between specified, selected limits, such as between the fracture and pore pressures.

Abstract: Processes and apparatus that continuously change the physical state and characteristics of drilling fluids at planned periodic intervals to consistently and correctly compensate for differing geological formation properties, wellbore characteristics, rate of penetration, solids removal efficiency, and other essential factors involved in the drilling process, comprising: initiating a system correction of a Minimum Base Required (“MBR”); and administering a dilutant to a drilling fluid according to the MBR. The system corrections may be performed recursively, adjusting the system's base dilutant and chemical product additions according to MBR. The drilling fluid consistency produced is based upon several drilling-rig specific parameters.

Abstract: A method of controlling pressure in a mud pump system includes generating a pressure limiting factor output using a pressure feedback input and a motor speed input to calculate a fluid conductance estimate, maintaining the pressure limiting factor output at a maximum value based on a pressure set-point, continuously updating a normal fluid conductance value based on the fluid conductance estimate while the pressure limiting factor output remains at the maximum value, freezing the normal fluid conductance value, if the pressure limiting factor output is less than the maximum value, calculating a change in fluid conductance based on the normal fluid conductance value and the fluid conductance estimate, generating at least one adaptive gain based on the change in fluid conductance, and controlling a motor speed of a pump in the mud pump system based on the at least one adaptive gain.

Abstract: An illustrative embodiment of a method is disclosed for assessing image quality of a down hole formation image, the method comprising collecting acquisition system data from a plurality of sensors down hole; applying a set of rules to the acquisition system data to obtain an acquisition quality indicator; and presenting the acquisition quality indicator at a surface location. A system is disclosed for performing the method.

Abstract: A downhole tool includes a downlinking system deployed in a downhole tool body having an internal through bore. The downlinking system includes a differential pressure transducer configured to measured a pressure difference between drilling fluid in the internal through bore and drilling fluid external to the tool (in the borehole annulus). The differential transducer is electrically connected with an electronic controller (deployed substantially anywhere in the drill string) that is configured to receive and decode pressure waveforms.

Abstract: An apparatus, method, and system described for generating pressure pulses in drilling fluid utilizing a flow throttling device which includes a controllable pulser operating sequentially within a downhole assembly within a drill string of a drill pipe. The system includes drilling fluid, fluid flow, and fluid drilling pump which when combined creates fluid flow into a bore pipe annulus within the downhole assembly creating a base line bore pipe pressure wherein bore pipe pressure is sensed via a sensor and information is sent to a Digital Signal Processor (DSP) that interprets the information. The DSP also receives information from an annulus pressure sensor that senses drilling fluid pressure as it returns to the pump. The DSP recognizes pressure variation input from the annulus pressure sensor and bore pipe pressure sensor and detects pressure variation providing signals as data information to the DSP, determining required action to adjust pulser operation.

Abstract: A tubular body with an axial bore includes an upper connection attached to a drillstring and a lower connection with a drill bit disposed thereon. Primary and backup cutter blocks are coupled to the tubular body and configured to selectively expand radially therefrom. An activation system within the tubular body is configured to selectively expand and collapse the primary and backup cutter blocks in response to changes in weight applied to the primary and backup cutter blocks.

Abstract: An arrangement and a method to control and regulate the bottom hole pressure in a well during subsea drilling at deep waters: The method involves adjustment of a liquid/gas interface level in a drilling riser up or down. The arrangement comprises a high pressure drilling riser and a surface BOP at the upper end of the drilling riser. The surface BOP has a gas bleeding outlet. The riser also comprises a BOP, with a by-pass line. The drilling riser has an outlet at a depth below the water surface, and the outlet is connected to a pumping system with a flow return conduit running back to a drilling vessel/platform.

Abstract: A method to control borehole fluid flow includes detecting a drilling condition and operating at least one valve in the drill string to place an exterior of the drill string in fluid communication with an interior of the drill string in response to detecting the drilling condition.

Abstract: A measurement-while-drilling mud pulser and a method for controlling a measurement-while-drilling mud pulser. The mud pulser includes a brushless DC motor that hydraulically controls a main restrictor valve that the mud pulser uses to generate mud pulses. Back EMF signals generated in the stator windings of the brushless DC motor are monitored and are used as the basis for commutating the brushless DC motor. The phase transitions in the back EMF signals can be used in governing stator energizations of the brushless DC motor to thereby govern its rotation. Relying on back EMF signals for commutation allows commutation to be performed without Hall Effect or other kinds of sensors, which can thereby reduce cost of the mud pulser and further increase reliability of the mud pulser by decreasing the number of high pressure sealings needed due to wires from Hall effect sensors, which are prone to develop leaks.

Abstract: Embodiments of systems, program product, and methods for controlling drilling fluid pressures are provided. These embodiments, for example, can provide dynamic density control with highly adaptive, real-time, process-control and are scalable to any rig, large or small, on land or water. Combined static and dynamic stresses and displacements can be determined continuously at strategic locations in and around the wellbore of a well so that insitu and operational induced pressure window limitations at specific weak-points or other locations of interest are controlled.

Abstract: A downhole tool comprises a body defining a fluid inlet and two or more fluid outlets. A valve arrangement cycles the proportion of fluid directed from the inlet to each of the outlets. One of the outlets may be associated with a fluid pressure responsive device, such as a cleaning blade.

Abstract: A method of controlling pressure in a wellbore can include determining a real time wellbore pressure PwbRT1 at a pressure sensor in the wellbore, calculating hydrostatic pressure Ph1 at the pressure sensor, determining a real time annulus pressure PaRT, calculating friction pressure Pf due at least to circulation of the fluid through the wellbore and depth in the wellbore, calculating a friction pressure correction factor CFPf1 equal to (PwbRT1?Ph1?PaRT)/Pf, and controlling operation of a pressure control device, based on the friction pressure correction factor CFPf1. The method can further include determining a desired wellbore pressure PwbD1 at the pressure sensor, calculating an annulus pressure setpoint PaSP1 equal to PwbD1?Ph1?(Pf*CFPf1), and adjusting the pressure control device as needed to maintain PaRT equal to PaSP1.

Abstract: The method of controlling the load on a drill bit drilling a hole by providing differential pressure across a seal area on a drilling assembly to increase the bit load and providing a relief valve from the annular area above the seal to the bore returning fluid to the surface to limit the maximum differential pressure to limit the maximum load allowed.

Abstract: Processes and apparatus that continuously change the physical state and characteristics of drilling fluids at planned periodic intervals to consistently and correctly compensate for differing geological formation properties, wellbore characteristics, rate of penetration, solids removal efficiency, and other essential factors involved in the drilling process. An embodiment of a process of the current invention comprises: initiating a system correction of a Minimum Base Required (“MBR”); and administering a dilutant to a drilling fluid according to the MBR. The system corrections may be performed recursively, adjusting the system's base dilutant and chemical product additions according to MBR. The drilling fluid consistency produced is based upon several drilling-rig specific parameters.

Abstract: A method of downlinking to a downhole tool located in a borehole is provided. The downhole tool detects transitions in the flow velocity of fluid circulating in the borehole at the downhole tool. To provide for the detection of the transitions fluid is pumped into the drillstring so that it circulates in the borehole at the downhole tool and the the pumping rate of fluid into the drillstring is either increased to a rate which overshoots a steady state pumping rate needed to produce a transition or is decreased to a rate which undershoots a steady state pumping rate needed to produce a transition.

Abstract: A drilling tool includes a hydraulically driven device (21) for advancing a drilling head (2) in a bore (5), and a flow limiter (30) arranged in a hydraulic conduit (25) of the advancing device (21) for adjusting an advancing speed of the drilling head (2) in the bore (5), with the flow limiter (30) having a pressure-actuated adjusting member (38) for adjusting flow of a hydraulic fluid in the hydraulic conduit means (25) in accordance with a flow volume of a rinsing fluid (7) for rinsing the bore.

Abstract: A system for reverse circulation in a wellbore includes equipment for supplying drilling fluid into the wellbore bit via at least an annulus of the wellbore and returning the drilling fluid to a surface location via at least a bore of a wellbore tubular. The system also includes devices for controlling the annulus pressure associated with this reverse circulation. An active pressure differential device may increase the pressure wellbore annulus to at least partially offset a circulating pressure loss. Alternatively, the system may include devices for decreasing the pressure in the annulus of the wellbore.

Abstract: A method of controlling pressure in a mud pump system includes generating a pressure limiting factor output using a pressure feedback input and a motor speed input to calculate a fluid conductance estimate, maintaining the pressure limiting factor output at a maximum value based on a pressure set-point, continuously updating a normal fluid conductance value based on the fluid conductance estimate while the pressure limiting factor output remains at the maximum value, freezing the normal fluid conductance value, if the pressure limiting factor output is less than the maximum value, calculating a change in fluid conductance based on the normal fluid conductance value and the fluid conductance estimate, generating at least one adaptive gain based on the change in fluid conductance, and controlling a motor speed of a pump in the mud pump system based on the at least one adaptive gain.

Abstract: An illustrative embodiment of a method is disclosed for assessing image quality of a down hole formation image, the method comprising collecting acquisition system data from a plurality of sensors down hole; applying a set of rules to the acquisition system data to obtain an acquisition quality indicator; and presenting the acquisition quality indicator at a surface location. A system is disclosed for performing the method.

Abstract: A method for determining formation integrity during drilling of a wellbore includes determining an annulus fluid pressure in a wellbore during drilling thereof. The annulus pressure is adjusted by a predetermined amount. Flow rate of drilling fluid into the wellbore is compared to drilling fluid flow rate out of the wellbore. At least one of a formation pore pressure and a formation fracture pressure is determined from the annulus pressure when the compared flow rates differ by a selected amount. The method alternatively to determining pore and/or fracture pressure includes determining a response of the wellbore to the adjusted fluid pressure and determining the optimum annulus fluid pressure from the wellbore response.

Abstract: A method and system of subterranean excavating that estimates a buoyancy force applied to a downhole excavating system from drilling fluid. The estimated buoyancy force is used to derive a true weight on bit (WOB) at the borehole bottom. The derived realized WOB is compared to a target WOB to obtain a change in WOB. Based on the change in WOB, the excavating system is adjusted so the realized WOB approximates the target WOB. The excavating system adjustment includes applying a compensating force to the string. Compensating forces can be produced by manipulating a block assembly or deploying a thruster device in the string.

Abstract: A tubular downhole tool string component having a sidewall with a fluid passageway formed therein between a first end and second end, and a valve mechanism disposed within the fluid passageway adapted to substantially cyclically build-up and release pressure within the fluid passageway such that a pressure build-up results in radial expansion of at least a portion of the sidewall and wherein a pressure release results in a radial contraction of the portion of the sidewall. The valve mechanism disposed within the fluid passageway comprises a spring. Radial expansion and contraction of the portion of the sidewall varies a weight loaded to a drill bit disposed at a drilling end of the drill string.

Abstract: A system and method is described for use and return of drilling fluid/cuttings from a well, which is drilled on the ocean floor, in connection with offshore related oil production and gas production, where, from a drilling rig or drilling vessel (10), a drill stem (12) runs down into the bore hole and where a blowout preventer (BOP) is placed on said well, without mounting a riser between the rig or the vessel and said blowout preventer. A sealing and pressure-regulating device (16) is arranged on the blowout preventer (14) arranged to regulate the level of the drilling fluid, and thus the outlet pressure of the drilling fluid in said sealing and pressure-regulating device, and a pump module (18) is set up at a suitable distance adjacent said sealing and pressure-regulating device, where the pump module is arranged to pump said drilling fluid up to the ocean surface via an external return pipe.

Abstract: A method for detecting a change in a wellbore fluid includes estimating at least two pressure differences in the wellbore fluid and estimating a change in a density of the fluid using the at least two pressure differences. The density change may be estimated by the equation, ??=(?Pbefore—influx??Pafter—influx)/(g×?TVD), wherein ?P is a fluid pressure difference between two points along the wellbore, ? is a mean value of density of the fluid between the two points, g is gravity and ?TVD is a vertical distance between the two points. The method may include estimating a density change using an estimated inclination of the wellbore. An apparatus for estimating density changes includes at least two axially spaced apart pressure sensors. The sensor positions may be switched to estimate a correction term to reduce a relative offset between the two pressure sensors.

Abstract: A riserless mud recovery system including a mud return line secured by an anchor is disclosed. Some system embodiments for drilling a well bore in an offshore location having a water surface and a subsea formation include an offshore structure positioned on a platform at a water surface, a drill string for forming the well bore suspended from the offshore structure, a drilling fluid source on the platform for supplying drilling fluid through the drill string, a suction module for collecting the drilling fluid emerging from the well bore, a return pipe coupled to the suction module, a pump for receiving the drilling fluid from the suction module and pumping the drilling fluid through the return pipe to a location at the water surface, and an anchor for securing the return pipe, where the anchor is coupled to the return pipe and the subsea formation.

Abstract: Embodiments of systems, program products, and methods for controlling drilling fluid parameters are provided. These embodiments, for example, provide dynamic density control with highly adaptive, real-time, process-control and are scalable to any rig, large or small, on land or water. Combined static and dynamic stresses and displacements can be determined continuously at strategic locations in and around the wellbore of a well so that insitu and operational induced pressure window limitations at specific weak-points or other locations of interest are controlled.

Abstract: A bottom hole assembly in a casing-while-drilling operation is retrieved by reducing the density of the fluid in the casing string above the bottom hole assembly, creating an upward force on the bottom hole assembly. As the bottom hole assembly moves upward in the casing string, fluid is pumped into the upper end of the annulus and displaced fluid flows out of the upper end of the casing string. The flow rate of the fluid flowing into the upper end of the annulus and the flow rate of the displaced fluid flowing out of the casing string are monitored and compared.

Abstract: A method of controlling operation of a rock drilling rig, and a rock drilling rig. A rate of flow of a flushing medium of the rock drilling rig is determined, and the operation of the rock drilling rig is controlled on the basis of the determined rate of flow by influencing pressure of the flushing medium.

Abstract: A method of drilling a bore hole in a fractured formation. A drill pipe is deployed into the borehole, whereby an annular space is formed between the drill pipe and the borehole wall. A drilling fluid is pumped, by means of primary pumps, into the borehole via an internal conduit of the drill pipe and a drill pipe fluid outlet present in the vicinity of a distal end of the drill pipe. The annular space is pressure sealed using a pressure seal such as a rotating head on a BOP. A well control fluid is pumped into the annular space via a well control conduit that fluidly connects the annular space, in a location between the pressure seal and the drill pipe fluid outlet, to a backpressure system. The well control fluid is pressure-balanced against the pressure seal and the backpressure system.

Abstract: A method for controlling a peripheral drilling operation involves obtaining a first property of a first drilling operation component associated with the peripheral drilling operation, via a wireless network, obtaining a second property of a second drilling operation component associated with the peripheral drilling operation, generating a control signal for the first drilling operation component, based on the first property and the second property, and communicating the control signal to the first drilling operation component, via the wireless network, where the first drilling operation component is adjusted, based on the control signal, to control the peripheral drilling operation.

Abstract: A method for monitoring drilling mud properties, the drilling mud being transported through a well drilling system and stored in a mud pit includes directing the flow of drilling mud in the well drilling system from the mud pit to a sampling unit. A sample of the drilling mud from the mud pit is obtained. At least one mud property of the sampled drilling mud is sensed automatically and in real time to obtain a condition value. If the condition value is within a set point range for the mud property the drilling mud is returned to the mud pit. The drilling mud is directed to a centrifuge for adjustment of the mud property if the condition value is outside the set point range. The drilling mud from the centrifuge is returned to the mud pit after the mud property has been adjusted.

Abstract: An APD Device provides a pressure differential in a wellbore to control dynamic pressure loss while drilling fluid is continuously circulated in the wellbore. A continuous circulation system circulates fluid both during drilling of the wellbore and when the drilling is stopped. Operating the APD Device allows wellbore pressure control during continuous circulation without substantially changing density of the fluid. The APD Device can maintain wellbore pressure below the combined pressure caused by weight of the fluid and pressure losses created due to circulation of the fluid in the wellbore, maintain the wellbore at or near a balanced pressure condition, maintain the wellbore at an underbalanced condition, reduce the swab effect in the wellbore, and/or reduce the surge effect in the wellbore. A flow restriction device that creates a backpressure in the wellbore annulus provides surface control of wellbore pressure.

Abstract: In one aspect of the invention, a downhole tool string component comprises a fluid passageway formed between a first and second end. A valve mechanism is disposed within the fluid passageway adapted to substantially cyclically build-up and release pressure within the fluid passageway such that a pressure build-up results in radial expansion of at least a portion of the fluid passageway and wherein a pressure release results in a contraction of the portion of the fluid passageway. The valve mechanism disposed within the fluid passageway comprises a spring. Expansion and contraction of the portion of the fluid passageway varies a weight loaded to a drill bit disposed at a drilling end of the drill string.

Abstract: A steering tool configured for making azimuthal and non-azimuthal formation evaluation measurements is disclosed. In one embodiment a rotary steerable tool includes at least one formation evaluation sensor deployed in the steering tool housing. The steering tool may include, for example, first and second circumferentially opposed formation evaluation sensors or first, second, and third formation evaluation sensors, each of which is radially offset and circumferentially aligned with a corresponding one of the steering tool blades. The invention further includes methods for geosteering in which a rotation rate of the steering tool housing in the borehole (and therefore the rotation rate of the formation evaluation sensors) is controlled. Steering decisions may be made utilizing the formation evaluation measurements and/or derived borehole images.

Abstract: A downhole tool includes a tubular body having an upper connection and a lower connection and an axial borehole therethrough, wherein the upper and lower connections are configured to connect to a drilling assembly. The downhole tool further includes at least one expandable component coupled to the tubular body and configured to selectively extend radially therefrom and an actuation mechanism configured to selectively extend the at least one component in response to a change in a circulating fluid pressure in the axial borehole.

Abstract: A method of controlling one or more operating pressures within a subterranean borehole that includes a choke assembly is disclosed. The choke assembly may include a housing having an inlet passage, an axial bore, and a chamber, wherein a portion of the axial bore forms an outlet passage, and a choke member adapted for movement in the housing to control the flow of a fluid from the inlet passage to the outlet passage. The method may include applying a closing force to move the choke member toward a closed position, and applying a bias force to the choke member when in the closed position to reduce an overpressure required to initiate movement of the choke member from the closed position.

Abstract: A method of reducing drilling fluid pressure during subsea drilling, where drilling fluid is pumped down into a borehole and then flows back to a drilling rig via the lined and/or unlined sections of the borehole and a liner, wherein the drilling fluid pressure is controlled by pumping drilling fluid out of the liner at the seabed, and where the liner annulus above the drilling fluid is filled with a riser fluid having a density different from that of the drilling fluid.

Abstract: An arrangement and a method to control and regulate the bottom hole pressure in a well during subsea drilling at deep waters: The method involves adjustment of a liquid/gas interface level in a drilling riser up or down. The arrangement comprises a high pressure drilling riser and a surface BOP at the upper end of the drilling riser. The surface BOP havs a gas bleeding outlet. The riser also comprises a BOP, with a by-pass line. The drilling riser has an outlet at a depth below the water surface, and the outlet is connected to a pumping system with a flow return conduit running back to a drilling vessel/platform.