Abstract: A method for altering flow conditions in a porous media containing hydrocarbons includes the steps of preparing a mixture of a surfactant, a co-surfactant and a carrier fluid; transporting the mixture to the porous media; and holding the mixture in the porous media in the presence of water for a period of time sufficient to form a water film on the surfaces of the porous media.

Abstract: A beamless mechanic-reversing long stroke pumping unit is provided for petroleum production in diverse types of oil fields. Its mechanic-reversing system consists of differentials, brakes, etc. With two differentials assembled together, taper gears inside them perform revolution and rotation, enabling the pumping unit to achieve direction change and speed change mechanically. The stroke length of the pumping unit can reach 8 meters or longer, and the adjustment process is more convenient than most, by merely tuning the position of the proximity switches. Abrasion of the chains typically caused due to resetting of a motor frequently during operation, is eliminated in this pumping unit. The pumping unit has more reliable operation performance, more convenient maintenance, lower costs, better energy saving effects, and can be applied in land oil fields, offshore oil fields, oil wells with low permeability, etc.

Abstract: A downhole well pumping assembly has a shroud with an upper section and a lower section sealed from one another. A submersible pump and a gas separator are housed within the upper section of the shroud. The gas separator has a liquid outlet in fluid communication with an intake of the pump, and a gas outlet in fluid communication with the gas outlet in the shroud. A motor is housed within the lower section of the shroud, the motor being coupled to the gas separator for rotating the gas separator and the pump. A well fluid lower inlet is in the shroud below the motor and a well fluid lower outlet is in the shroud above the motor.

Abstract: Geothermal energy is recovered from magma via a vent of volcano by a longitudinally displaceable, closed system of one tube for injecting working condensed water and the other production tube for return of heated water, and a number of heating tube members connected to front portions of the tubes. The water may be assisted in its return by a pump. The tubes are capable to be advanced relative to a stationary shelter building by a drive means disposed securely at the vent. The front portions are articulated and/or flexible, and provided with a chassis. The tubes may be in co-axial relation and the outer injection tube is used as the heat economizer and insulator tube, and provided with sank and movable scraper members to remove a scale. A heat exchange means is operable to recover thermal energy from the water.

Abstract: An example flow control device includes a body having an inlet and an outlet and a flow chamber extending therebetween. The flow chamber is configured to convey a fluid composition comprising a desired and an undesired fluid from the inlet to the outlet. A nozzle is arranged at the outlet and in fluid communication with the flow chamber, and at least one helical groove is defined along at least a portion of an axial length of the flow chamber. The at least one helical groove is configured to impart rotational motion to the fluid composition and thereby force at least some of the undesired fluid into the at least one helical groove and slow a progress of the undesired fluid along the axial length of the flow chamber.

Abstract: A method to extract oil for a pool of oil in the ground utilizes an interconnected series of rotating helical blades extending from the surface of the ground through a canted bore to the pool of oil. The blades can be staggered and interconnected with a gear arrangement that moves oil from pool to pool and up to the surface of the ground.

Abstract: A method of gas production from a field containing natural gas processing particularly for transport of stranded gas to conserve resources and reduce emissions includes extracting gas a gas supply from a plurality of individual gas wells in the field and initially at the individual gas wells providing a recovery unit having a production capacity matching that of the well for carrying out liquid recovery from the gas supply and compression of the natural gas. When a production rate of the well declines to a low level, typically to about 20% of the original, the recovery unit is removed for redeployment either at a central plant or at other wells which are still at the high production and is substituted by a dehydration system and gas compressor arranged to fill portable pressure vessels typically on trucks for transporting the compressed natural gas to a main pipe line.

Abstract: Drain wells can be used to direct a fluid to a central production well in a subsurface well system. Subsurface well systems can include a production well extending from the earth's surface, a collection region having a fluid connection to the production well and either being contiguous with the production well or comprising a collection well that intersects or is in fluid communication with the production well, and at least one branched drain well extending laterally from the production well and including one or more branches that extend from the at least one branched drain well, wherein at least one of the one or more branches intersects or is in fluid communication with the collection region.

Abstract: A deliquification pump for deliquifying a well comprises a fluid end pump adapted to pump a fluid from a wellbore. In addition, the deliquification pump comprises a hydraulic pump adapted to drive the fluid end pump. The hydraulic pump includes a first internal pump chamber and a first pump assembly disposed in the first chamber. The first pump assembly includes a piston having a first end, a second end, and a throughbore extending between the first end and the second end. In addition, the first pump assembly includes a first wobble plate including a planar end face axially adjacent the second end of the piston and a slot extending axially through the first wobble plate. The first wobble plate is adapted to rotate about the central axis relative to the housing to axially reciprocate the piston and cyclically place the throughbore of the piston in fluid communication with the slot.

Abstract: A flow restrictor device for production tubing comprising an obstructing member. The flow restrictor is arranged for movement between a first position where the obstructing member is located so as to form a seal with an edge of an aperture formed in a wall of said production tubing and is arranged to prevent fluid flow through said aperture, and a second position where the obstructing member is located so that the aperture is unobstructed. The flow restrictor further comprises a retaining arrangement for restricting possible locations of said obstructing member to said first position, second position and positions therebetween. The aperture allows fluid communication between the exterior and interior of the production tubing.

Abstract: A method of drilling and producing from an offshore structure, comprising drilling a first well from the offshore structure with a drilling riser; completing the first well with a first subsurface tree; connecting the first subsurface tree to a manifold; drilling a second well from the offshore structure with a drilling riser; completing the second well with a second subsurface tree; connecting the second subsurface tree to the manifold; and connecting a production riser to the manifold and the offshore structure.

Abstract: Disclosed are systems and methods of producing from multiple production zones with a single trip multi-zone completion system. One method includes arranging an outer completion string within an open hole section of a wellbore, the outer completion string having at least one sand screen disposed thereabout, extending a production tubing within the outer completion string, the production tubing having at least one interval control valve disposed thereon, communicably coupling the production tubing to the completion string at a crossover coupling having one or more control lines coupled thereto, actuating the at least one interval control valve to initiate production into the production tubing at the at least one interval control valve, and measuring one or more fluid and/or well environmental parameters external to the outer completion string with a surveillance line communicably coupled to one or more control lines at the crossover coupling.

Abstract: A method, software, and apparatus for controlling a pump configured to pump liquid out of a well. Such control may involve determining whether a production rate of gas from the well is increasing, decreasing, or steady, and whether to switch the pump between an OFF state and an ON state. Whether the pump is switched may depend upon whether the production rate of the gas is determined to be increasing, decreasing, or steady.

Abstract: A system for use with a well having multiple zones can include multiple well screens which filter fluid flowing between a tubing string and respective ones of the zones, at least one optical waveguide which senses at least one property of the fluid as it flows between the tubing string and at least one of the zones, multiple flow control devices which variably restrict flow of the fluid through respective ones of the well screens, and multiple pressure sensors which sense pressure of the fluid which flows through respective ones of the well screens. A tubing string for use in a subterranean well can include at least one well screen, at least one flow control device which selectively prevents and permits substantially unrestricted flow through the well screen, and at least one other flow control device which is remotely operable, and which variably restricts flow through the well screen.

Abstract: Embodiments described herein provide a system and methods for the production of hydrocarbons. The method includes flowing a stream directly from a hydrocarbon reservoir to a cavern and performing a phase separation of the stream within the cavern to form an aqueous phase and an organic phase. The method also includes flowing at least a portion of the aqueous phase or the organic phase, or both, directly from the cavern to a subsurface location and offloading at least a portion of the organic phase from the cavern to a surface.

Abstract: The present invention relates to a managed pressure and/or temperature drilling system (300) and method. In one embodiment, a method for drilling a wellbore into a gas hydrates formation is disclosed. The method includes drilling the wellbore into the gas hydrates formation; returning gas hydrates cuttings to a surface of the wellbore and/or a drilling rig while controlling a temperature and/or a pressure of the cuttings to prevent or control disassociation of the hydrates cuttings.

Abstract: A motor winding wire. The motor winding wire may be configured for use in, and direct exposure to, a hydrocarbon environment. The motor winding wire may be electrically insulated by one polymer layer, whereas another, outer, polymer layer is employed to provide moisture resistance as well as other contaminant and hydrocarbon environment shielding to the underlying layer. Additionally, this manner of polymer layering over the motor winding wire is achieved in a manner cognizant of the limited dimension of the motor winding wire.

Abstract: Disclosed is a wellbore configuration for use in coal bed gas production comprising tubing and down hole equipment made from non-sparking materials which can be mined out with the coal.

Abstract: A method for preventing the production and formation of loose sand particles during production of a production fluid includes converting in the production zone both a loose sand particle into a magnetized loose sand particle and a cemented sand particle into a magnetized cemented sand particle. The method includes introducing a magnetic source into a wellbore. The method includes operating the magnetic source such that a continuous magnetic field is generated and the continuous repulsive magnetic force is less than the mean cementation strength. The method includes producing the production fluid from the production zone to the wellbore at a production rate. The method includes maintaining the magnetic source and the production rate of the hydrocarbon fluid such that within the distance from the magnetic source the production fluid drag force is less than or equal to the continuous repulsive magnetic force.

Abstract: A method of selecting an injectate for recovering liquid hydrocarbons from a reservoir includes designing a plurality of injectates, calculating a net present value of each injectate, and selecting a candidate injectate based on the net present value. For example, the candidate injectate may be selected to maximize the net present value of a waterflooding operation.

Abstract: The present invention relates to an annular barrier system for expanding an annular barrier in an annulus between a well tubular structure and an inside wall of a borehole downhole. The annular barrier system comprises an annular barrier having a tubular part for mounting as part of the well tubular structure, the annular barrier further comprising an expandable sleeve surrounding the tubular part, at least one end of the expandable sleeve being fastened in a fastening means of a connection part in the tubular part. The annular barrier system also comprises a tool for expanding the expandable sleeve by letting a pressurised fluid through a passage in the tubular part into a space between the expandable sleeve and the tubular part.

Abstract: Systems and methods for thermal recovery of shallow bitumen using increased permeability inclusions. A method of producing hydrocarbons from a subterranean formation includes the steps of: propagating at least one generally planar inclusion outward from a wellbore into the formation; injecting a fluid into the inclusion, thereby heating the hydrocarbons; and during the injecting step, producing the hydrocarbons from the wellbore. A well system includes at least one generally planar inclusion extending outward from a wellbore into a formation; a fluid injected into the inclusion, hydrocarbons being heated as a result of the injected fluid; and a tubular string through which the hydrocarbons are produced, the tubular string extending to a location in the wellbore below the inclusion, and the hydrocarbons being received into the tubular string at that location.

Abstract: An apparatus for controlling the flow of downhole fluids comprises a body having a throughbore and at least one port extending through a sidewall of the body to enable fluid communication between the throughbore and an exterior of the body. The apparatus comprises a flow control device for controlling the flow of fluids through the port. The flow control device is arranged to change configuration between a closed configuration in which fluid flow through the port is restricted and an open configuration in which fluid flow through the port is permitted. The apparatus further comprises an actuator mechanism associated with the flow control device for selective actuation of the flow control device to change the configuration of the flow control device between the closed and open configurations.

Abstract: A top-mounted digital-control tower pumping unit includes a tower frame (1), a power system (2), a drive system, a control system (3), a balance weight box (4), a balance weight positioning cable (5), a driving cable (6), a plurality of cable hangers (7) and a guide wheel mechanism. The guide wheel mechanism is fixed on an operation platform by a rotating shaft, which is convenient for the operator to move the guide wheel mechanism aside during the oil well work-over. The control system, the power system, and the drive system are all mounted closely on an operating platform on the top of the tower frame. The top-mounted digital-control tower pumping unit of the present invention has the advantages of simple structure, convenient maintenance, low cost, stable operation and small noise.

Abstract: Disclosed are systems and methods of producing from multiple production zones with a single trip multi-zone completion system. One method includes arranging an outer completion string within a wellbore adjacent the one or more formation zones, the outer completion string having at least one sand screen arranged thereabout and a flow control device movably disposed within the sand screen, locating an insert string within the outer completion string, the insert string having at least one control and data acquisition module disposed thereon that has one or more mechanical coupling mechanisms, locating the flow control device with the one or more mechanical coupling mechanisms, and moving the flow control device between a closed position and an open position with the one or more mechanical coupling mechanisms.

Abstract: There is disclosed a system adapted to transport two fluids, comprising a nozzle comprising a first nozzle portion comprising the first fluid; and a second nozzle portion comprising the second fluid, wherein the second nozzle portion has a larger diameter than and is about the first nozzle portion; and a tubular fluidly connected to and downstream of the nozzle, the tubular comprising the first fluid in a core, and the second fluid about the core; the first fluid comprising a crude oil having a total acid number greater than 1, and the second fluid comprising a basic solution having a pH greater than 8.

Abstract: Multiple zones of a wellbore are gravel packed and fractured in the same run-in trip into a wellbore. An insert string is subsequently extended into the wellbore in order to regulate and monitor production from each zone. Control lines located within the insert string and also along the sand face allow operators to monitor production operations, including measuring fluid and well environment parameters at each point within the system. One or more control and data acquisition modules included in the insert string are able to locate and move corresponding flow control devices arranged within respective sand screens adjacent each zone. Adjusting the position of the flow control device with a corresponding control and data acquisition module serves to choke or otherwise regulate the production flow rate through the sand screen, thereby allowing for the intelligent production of hydrocarbons from each zone.

Abstract: The present invention relates to recovery of hydrocarbons being released subsea in an uncontrolled manner. More specifically, the invention relates to an apparatus, process and system for the recovery of well stream products being released subsea in an uncontrolled manner, optionally under conditions that are conducive to the formation of gas hydrate crystals.

Abstract: A method of pumping an oilfield fluid from a well surface to a wellbore is provided that includes providing a clean stream; operating one or more clean pumps to pump the clean stream from the well surface to the wellbore; providing a dirty stream including a solid material disposed in a fluid carrier; and operating one or more dirty pumps to pump the dirty stream from the well surface to the wellbore, wherein the clean stream and the dirty stream together form said oilfield fluid.

Abstract: The invention relates to methods for extracting a kerogen-based product from subsurface shale formations. The methods utilize in-situ reactions of kerogen involving liquid phase chemistry at formation temperatures and pressures. These methods rely on chemically modifying the shale-bound kerogen to render it mobile, using chemical oxidants. In one embodiment, an oxidant is provided to the subsurface shale formation comprising kerogen in an inorganic matrix, the oxidant converting the kerogen to form organic acids, and forming a mobile kerogen-based product. The spent oxidant is regenerated in-situ to restore at least some of the original oxidation activity. At least a portion of the mobile kerogen-based product is recovered. The kerogen-derived product can be upgraded to provide commercial products.

Abstract: A surface drivehead drives a downhole pump by rotating a rod string at the surface. The downhole pump can be connected downhole to the rod string via a downhole latching mechanism. The surface drivehead has an assembly that can move the rod string upwards or downwards along an axis to either increase or decrease rod string tension. During rod string rotation, rod tension is monitored. If rod string tension changes during rotation, the surface drivehead can automatically compensate by moving the rod string upwards or downwards along the axis to either recapture or eliminate tension. In this way, the surface drivehead can maintain a substantially constant rod string tension to drive the downhole pump at high speeds.

Abstract: A downhole assembly of an artificial lift system includes: an adapter for connection to production tubing; a receptacle shaft; an up-thrust bearing; a centrifugal pump; and a down-thrust bearing. The receptacle shaft has a latch profile for receiving a latch fastener of a drive coupling and a torsional profile for mating with the coupling to longitudinally and torsionally connect thereto. The up-thrust bearing includes: a thrust driver longitudinally and torsionally connected to the receptacle shaft; and a thrust carrier connected to the adapter. The centrifugal pump includes: a diffuser connected to the adapter; a pump shaft torsionally connected to the receptacle shaft; and an impeller connected to the pump shaft. The down-thrust bearing includes: a thrust driver longitudinally and torsionally connected to the pump shaft; and a thrust carrier connected to the adapter.

Abstract: A downhole apparatus having an upper well stop disposed at the surface of a well and a lower well stop disposed in the well. The apparatus further includes a plunger disposed within the well, wherein the plunger has a first sleeve having an outer diameter and a ball valve disposed on the first sleeve, wherein the ball valve is configured to rotate between an open and a closed position.

Abstract: A sand control device is used for restricting the flow of particles from a subsurface formation into a tubular body within a wellbore during production operations. The sand control device is divided into compartments along its length that provide redundancy for particle filtration. Each compartment first comprises a base pipe. The base pipe defines an elongated tubular body having a permeable section and an impermeable section within each compartment. Each compartment also comprises a first filtering conduit and a second filtering conduit. The filtering conduits comprise filtering media and generally circumscribe the base pipe. The filtering conduits are arranged so that the first filtering conduit is adjacent to the non-permeable section of the base pipe, while the second filtering conduit is adjacent to the permeable section of the base pipe.

Abstract: An inflow control device controls the rate of fluid flow from a subsurface fluid reservoir into a production tubing string. The inflow control device includes a particulate screen to remove particulate matter from the reservoir fluid, and at least two flow restrictors. The flow restrictors are positioned on circumferentially opposite sides of the inflow control device and are connected by an isolated fluid passage. The flow restrictors limit the flowrate of reservoir fluid when the reservoir fluid has a high water or gas-to-oil ratio. The inflow control device also includes at least one pressure drop device that generates a pressure drop for the reservoir fluid in response to fluid pressure in the reservoir. The inflow control device also includes a choking apparatus that allows the flow of reservoir fluid to be shut off and the particulate screen cleaned while the inflow control device is in place in hole.

Abstract: The present invention discloses apparatuses, systems, and methods for operating a gas well. Some embodiments include a plunger apparatus configured to fall through a continuous water phase (including water slugs) in a gas producing well by overcoming pressure and drag forces from the water by having a sufficient mass, hydrodynamic profile, and sufficiently large area for passage of the continuous water. In one embodiment, a plunger body and plug mechanism are provided, wherein the plug mechanism has open and closed positions, which may be automatically changed or controlled by a surface or other control system, and wherein the plunger body and plug may be a physically integrated one-piece system, or an interoperable two piece system.

Abstract: A production system for producing hydrocarbons from a subterranean reservoir includes a wellhead including a housing and a head. The housing has a central axis, an upper end, a lower end, and an inner surface. The inner surface defines a passage extending axially through the housing. In addition, the inner surface of the housing includes an annular recess positioned between the upper end and the lower end. The housing also includes a first production port extending radially through the housing. Further, the system includes a casing hanger disposed within the housing. The casing hanger has an upper end, a lower end, an outer surface, and a through bore extending from the upper end to the lower end. The casing hanger also includes a plurality of circumferentially-spaced ports extending radially through the casing hanger from the through bore to the annular recess of the housing.

Abstract: Embodiments of the present invention relate to an apparatus and methods for enhanced well control in slim completions. An embodiment can include an electrical submersible pump (“ESP”) positioned within a casing and having at least a portion thereof extending outwardly from a production tubing positioned within the casing. The production tubing terminates adjacent a distal end portion of a pump discharge to thereby provide greater interstitial space between outer surfaces of the portion of the pump disposed to extend outwardly from the production tubing and inner walls of the casing. This increased interstitial space, for example, can assist in cost savings by reducing the rate of erosion damage to the ESP. Embodiments of the present invention can further include a valve connected to inner walls of the casing and positioned distal from the ESP to control the flow of hydrocarbons.

Abstract: A method and apparatus for improving the production efficiency of a well and preventing gas lock. The apparatus is a downhole pump and comprises a barrel, a reciprocating plunger and a body having a plurality of inlet valves. The apparatus does not require outlet valves. The body and inlet valves are positioned above the barrel and plunger, thus eliminating gas lock. Fluids enter the body through the valves and, during upstrokes of the plunger, are forced up the tubing string to the surface equipment. Modularity of the components permits pump components to be changed as the productivity of the well fluctuates and also allows production of more fluids with a smaller casing.

Abstract: A mobile water injection system and method for performing waterflooding in offshore reservoirs, and more particularly to enhance oil recovery in marginal offshore reservoirs is disclosed. The mobile water injection system and method include portable equipment, including a submersible pump to recover water from a body of water, a water storage tank, filtration and chemical treatment equipment to treat the recovered water, and an injection pump to pump the treated water at high pressure into the reservoir such that the residual oil is driven to adjacent production wells to increase oil recovery.

Abstract: A high speed swirling type centrifugal revolving pipeline device, which utilizes a spiral pipeline curling and revolving with different pipe radius and with different radius of curvature, comprising an inlet pipeline, at least two transport pipelines, and at least a pressuring and accelerating pipeline, to serve as transport pipeline for fluid to continue swirling up. At least a driving device is used to drive spiral pipeline. Spiral pipeline design and centrifugal force produced by high speed rotation are used to drive fluid to the highest water level swiftly and stably, to proceed with subsequent conversion of regenerated energy into electrical power.

Abstract: An example method for mobile workflow orchestration and job execution for a hydrocarbon recovery operation may include generating a workflow corresponding to the hydrocarbon recovery operation and providing the workflow to a first information handling system located at the site of the hydrocarbon recovery operation. The workflow may also be provided to a second information handling system remote from the site of the hydrocarbon recovery operation. Information regarding the workflow may be received from the first information handling system, and the workflow at the second information handling system may be updated based, at least in part, on the information received from the first information handling system.

Abstract: An oil shale formation may be treated using an in situ thermal process. Heat may be applied to the formation to raise a temperature of a portion of the formation to a pyrolysis temperature. Heat input into the formation may be controlled to raise the temperature of portion at a selected rate during pyrolysis of hydrocarbons within the formation. A mixture of hydrocarbons, H2, and/or other formation fluids may be produced from the formation.

Abstract: The system and method for steam production for extraction of heavy bitumen includes a method of mixing fuel and oxidizing gases, combusting the mixture, mixing combustion gas with water containing solids and organics, separating solids, using heat from the separated gas to produce distilled water, recycling the distillation facility brine with the combustion gas and removing solids thereof, generating steam from the distilled water and injecting the steam through an injection well or using it above ground for oil recovery. The system includes a combustion boiler, a direct contact steam generator, a gas-solids separator, and a heat exchanger with a water treatment facility like a distillation facility. The water feed of the present invention can be water separated from produced oil and/or low quality water salvaged from industrial plants, such as refineries and tailings as make-up water.

Abstract: A method for extracting bitumen from a subterranean oil sand deposit including: drilling a portion of the deposit; fragmenting the drilled deposit; drilling of the fragmented deposit to allow for flooding, wherein one or more wells are drilled to provide access to the deposit and retrieval of extracted bitumen, to form a drilled fragmented deposit; flooding the drilled fragmented deposit with a first flood volume of fluid to permit the first flood volume of fluid to admix with the fragmented first portion, to re lease heavy oil from any inert material so that the heavy oil floats within the first flood volume of fluid in the drilled fragmented deposit to form a flooded first portion; recovering the heavy oil; and repeating the above for each additional portions.

Abstract: The present invention is directed to methods for harnessing flow-induced electrostatic energy in a tubular length and using this energy to power electrical devices (e.g., flowmeters, electrically-actuated valves, etc.). The present invention is also directed to corresponding systems through which such methods are implemented.

Abstract: A hydraulic oil well pumping arrangement employs a compensating type hydraulic pump, a directional valving arrangement and a proportioning valving arrangement. When the directional valve is energized, oil is directed to the rod end of the hydraulic cylinder. In one embodiment, a time delay halts the movement of the sucker rod or pumping string to allow accumulation of oil in a slow following well. In another embodiment, the pumping string rapidly falls to the bottom of the stroke in order to shake or jar debris from the string.

Abstract: A latch system configured to permit one-way automatic passing of a swabbing tool. The latch system having a housing in communication with a well bore and a latch assembly housing a latch member with a latch. The latch is configured to selectively translate through an aperture in the housing. The latch assembly utilizes a biasing member to selectively control the location of the latch. The biasing member is sealingly separated from exposure to discharge fluids within the housing. While in an extended position, the latch allows the removal of the swabbing tool from the well bore but prevents the passing of the swabbing tool from a swab tube.

Abstract: A process for controlling the production of loose sand particles within an underground formation through the use of magnetic forces is provided. The loose sand particles are magnetized and then subjected to a magnetic field of sufficient strength such that the operator can control the movement of the loose sand particles within the underground formation. In some instances, the present invention can provide an efficient process for keeping the loose sand particles within the formation, and thereby prolonging the useful life of the downhole equipment. In other instances, the present invention can provide an efficient process for sweeping the loose sand particles out of the underground formation in a controlled fashion. The present invention includes at least three embodiments for magnetizing the loose sand particles, including direct magnetization, contacting the sand particles with a magnetizing reagent, and contacting the sand particles with paramagnetic nanoparticles.

Abstract: An offshore universal riser system may include a valve module which selectively permits and prevents fluid flow through a flow passage extending longitudinally through a riser string. An anchoring device may releasably secure the valve module in the passage. A method of constructing a riser system may include the steps of installing the valve module in the passage, and installing at least one annular seal module in the passage. The annular seal module may prevent fluid flow through an annular space between the riser string and a tubular string positioned in the passage. Drilling methods may include injecting relatively low density fluid compositions into the annular space, and selectively varying a restriction to flow through a subsea choke in a drilling fluid return line. The riser string, including housings for the various modules and external control systems, may be dimensioned for installation through a rotary table.