This disclosure relates to the field of pressure control of wells drilled through subsurface earthen formation. More specifically, the present disclosure relates to maintaining wellbore pressure in the event of certain drilling conditions, such as drilling fluid lost to an exposed subsurface formation and the influx of gas into the well from a formation.
U.S. Pat. No. 7,562,723 shows one example embodiment of a “managed pressure drilling” control system. The system shown in the '723 patent may be used to maintain a selected pressure in a wellbore while drilling fluid pumps (rig mud pumps) are operating and while such pumps are switched off for purposes such as adding or removing a segment (“joint” of “stand”) of a drill string. The system shown in the '723 patent comprises logic operable to detect influx of fluid into the well from a subsurface formation as well as loss of fluid from the well into a subsurface formation. The system shown in the '723 patent may be used with land-based drilling as well as marine drilling (i.e., drilling subsurface formations below the bottom of a body of water).
U.S. Pat. No. 8,413,724 issued to Carbaugh et al. describes a “riser gas handler.” In the event of influx of gas into a well during marine drilling, where a “riser” connects a subsea well control apparatus to a drilling platform on the water surface, the gas expands in volume as it travels upwardly through the liquid column in the riser. As the gas expands in volume, the hydrostatic pressure exerted by the fluid column in the riser is reduced, and the pressure in the well may correspondingly increase. The pressure increase in the riser may at some point exceed the pressure bearing capacity of the riser. The device shown in the '724 patent is intended to divert fluid in the riser that contains gas to flow lines external to the riser. Such flow lines may have a pressure capacity much greater than that of the riser, thus enabling the gas to be removed from the well using known procedures to stop influx of fluid into a well from a subsurface formation.
Because subsurface formation fluid pressures can change substantially and unpredictably, it is desirable to automate systems such as those described above in the Reitsma and Carbaugh et al. patents. More specifically, such automation may be applicable to and coordinated with both such systems as well as with a well pressure control apparatus (blowout preventer—“BOP”) disposed proximate the water bottom and connected to the base of the riser.
The drill string 112 supports a bottom hole assembly (BHA) 113 that may include the drill bit 120, a mud motor 118, a measurement and/or logging-while-drilling (MWD/LWD) sensor suite 119 that may comprise a pressure transducer 116 to determine the annular pressure in the well 106. The drill string 112 may include a check valve (not shown) to prevent backflow of fluid from the annulus 115 into the interior of the drill string 112. The MWD/LWD suite 119 may comprise a telemetry package 122 that is used to transmit pressure data, MWD/LWD sensor data, as well as drilling information to be received at the Earth's surface in the form of modulation of the flow rate and/or pressure of drilling fluid being pumped through the interior of the drill string 112. While
The drilling process may use a drilling fluid 150, which may be stored in a reservoir 136. The reservoir 136 is in fluid communication with one or more rig mud pumps 138 which pump the drilling fluid 150 through a conduit 140. The conduit 140 is connected to the uppermost segment or “joint” of the drill string 112. The uppermost segment of the drill string may pass through a rotating control head or rotating control device (RCD) 142. The RCD 142 internally urges spherically shaped elastomeric sealing elements to rotate upwardly, closing around the drill string 112 and isolating the fluid pressure in the annulus 115, but still enabling drill string rotation and longitudinal motion. The drilling fluid 150 is pumped down through an interior passage in the drill string 112 and the BHA 113 and exits through nozzles or jets in the drill bit 120, whereupon the drilling fluid 150 circulates drill cuttings away from the drill bit 120 and returns the cuttings upwardly through the annulus 115 between the drill string 112 and the well 106 and through the annular space formed between the casing 108 (or riser as will be explained with reference to
Thereafter the drilling fluid 150 may proceed to what is generally referred to herein as a backpressure system 131. The drilling fluid 150 enters the backpressure system 131 and may flow through a flow meter 126. The flow meter 126 may be a mass-balance type or other of sufficiently high-resolution to meter the drilling fluid 150 flow out of the well 106. Using measurements from an inlet flowmeter 152 disposed between the rig mud pumps 138 and the drill string 112, which flow meter 152 may also be a mass-balance type or may be a Coriolis-type flow meter, a system operator will be able to determine how much drilling fluid 150 has been pumped into the well 106 through the drill string 112. The use of a pump stroke counter may also be used in place of the inlet flowmeter 152. Typically the amount of drilling fluid 150 pumped into the well 106 and returned from the well 106 are essentially the same in steady-state conditions when compensated for additional volume of the well 106 that is drilled. In compensating for transient effects and the additional volume of the well 106 being drilled and based on differences between the amount of drilling fluid 150 pumped into the well 106 and drilling fluid 150 returned from the well 106, the system operator is be able to determine whether drilling fluid 150 is being lost to the formation 104, which may indicate that formation fracturing or breakdown has occurred, i.e., a significant negative fluid differential. Likewise, a significant positive differential would be indicative of formation fluid entering into the well 106 from the subsurface formations 104.
The returning drilling fluid 150 may proceed to a wear resistant, controllable orifice choke 130. It will be appreciated that there exists chokes designed to operate in an environment where the drilling fluid 150 contains substantial drill cuttings and other solids. The controllable orifice choke 130 is preferably one such type and is further capable of operating at variable pressures, variable openings or apertures, and through multiple duty cycles. The drilling fluid 150 exits the controllable orifice choke 130 and flows through a first valve arrangement 5. The drilling fluid 150 can then be processed by an optional degasser 1 or directly to a series of filters and shale shakers 129, designed to remove contaminants, including drill cuttings, from the drilling fluid 150. The drilling fluid 150 is then returned to the reservoir 136. A flow loop 119A, is provided in advance of a valve arrangement 125 for conducting drilling fluid 150 directly to the inlet of a backpressure pump 128. In other embodiments, the backpressure pump 128 inlet may be provided with fluid from the reservoir 136 through a conduit 119B, which is in fluid communication with a trip tank 2. The trip tank 2 may be used on a drilling rig to monitor drilling fluid gains and losses during drill string “tripping” operations (i.e., withdrawing and inserting the full drill string 112 or substantial subset thereof from the well 106). In the present example embodiments, the trip tank 2 functionality may be maintained. A second valve arrangement 125 may be used to select flow loop 119A, conduit 119B or to isolate the backpressure system. While the backpressure pump 128 is capable of utilizing returned drilling fluid 150 to create a backpressure by selection of flow loop 119A, it will be appreciated that the returned drilling fluid 150 could have contaminants that would not have been removed by the shale shakers 129. In such case, the wear on backpressure pump 128 may be increased. Therefore, it may be preferable for the drilling fluid supply for the backpressure pump 128 to be from conduit 119B to provide reconditioned drilling fluid to the inlet of the backpressure pump 128.
In operation, the second valve arrangement 125 may be operated to select either flow loop 119A or conduit 119B, and the backpressure pump 128 is then engaged to ensure sufficient fluid flow passes through the upstream side of the controllable orifice choke 130 to be able to maintain a selected fluid pressure in the annulus 115, even when there is no drilling fluid 150 flow from the annulus 115. In the present embodiment, the backpressure pump 128 may be capable of providing up to approximately 2200 psi (15168.5 kPa) of pressure; though higher pressure capability pumps may be selected at the discretion of the system designer. It will be appreciated that the pump 128 would be positioned in any manner such that it is ultimately in fluid communication with the annulus 115, the annulus being the discharge conduit of the well.
By placing a pump 220 in fluid communication with the interior of the liner 214 near the water bottom 208, or making a similar fluid connection to the interior of the drilling riser 212 at a selected elevation, which may be above the water bottom 208, the returning drilling fluid may be pumped out of the annulus 230 and up to the drilling unit 201. The annular volume in the riser 212 above the drilling fluid level may be filled with a riser fluid that is of a different composition than the drilling fluid.
The drilling fluid pressure at the water bottom 208 may be controlled from the drilling unit 201 by selecting the inlet pressure to the pump 220. Inlet pressure to the pump 220 may be selected by controlling an operating rate of the pump, for example and without limitation, controlling a rotation rate of an impeller of a centrifugal pump or controlling a shaft rotation rate of a positive displacement pump.
In order to prevent the drilling fluid pressure from exceeding an acceptable level (e.g., in the case of a pipe trip), the drilling riser 12 may be provided with a dump valve. A dump valve of this type may be set to open at a particular predetermined pressure for outflow of drilling fluid to the body of water (10A in
The following describes a non-limiting example of a method and device illustrated in the accompanying drawings, in which, as noted above,
Reference number 201 denotes a drilling unit comprising a support structure 202, a deck 204 and a derrick 206. The support structure 202 is placed on the water bottom 208 (or the support structure 202 may be affixed to flotation devices as is well known in the art) and projects above the surface 10 of the water. The riser section of the surface casing or liner 214 extends from the water bottom 208 up to the deck 204, while the liner 214 extends further down into the well 125. The riser 212 may be provided with required well head valves, such as a subsea blowout preventer assembly (“BOP”) 204. The BOP 204 may include various devices known in the art to close the borehole 15 hydraulically when the drill string 216 is in the well 215, or when there is no drill string present.
The drill string 216 projects from the deck 204 and down through the liner 214. A first pump pipe 217 in some embodiments may be coupled to the riser section 212 near the water bottom 208 via a valve 218 and the opposite end portion of the pump pipe 217 is coupled to a pump 220 placed near the seabed 208. A second pump pipe 222 extends from the pump 220 to a collection tank 224 for drilling fluid on the deck 204.
A tank 226 for a riser fluid communicates with the riser 212 via a connecting pipe 228 at the deck 204. The connecting pipe 28 may have a volume flow meter (not shown). In some embodiments, the density of the riser fluid is less than that of the drilling fluid. The riser fluid may be a gas in which case the tank 226 and connecting pipe 228 can be omitted.
The power supply to the pump 220 may be via an electrical or hydraulic cable (not shown) from the drilling unit 201. The pump 220 may be electrically driven, or may be driven hydraulically by means of oil that is circulated back to the drilling unit 1 or by means of water that is dumped in the sea from the pump 220 power fluid discharge. The pressure at the inlet to the pump 20 is selected from the drilling unit 201.
The drilling fluid is pumped down through the drill string 216 in a manner that is known in the art, for example, using a mud pump 227 which lifts drilling fluid from a storage tank 224 and discharges drilling fluid (“mud”) under pressure to the interior of the drill string 216. The drilling fluid may be returned to the deck 4 through an annulus 30 between the liner or casing 214 (and the riser 212) and the drill string 216 through a return line 229. When the pump 220 is started, the drilling fluid is returned from the annulus 230 via the pump 220 to the storage tank 224 on the deck 204. Using such a system it is possible to obtain a significant reduction in the pressure of the drilling fluid in the well 215 and consequently a higher mud density may be used creating a different pressure gradient.
The riser 212 may include auxiliary fluid lines 200, 202 that may be in selective hydraulic communication with the borehole 15 below the wellhead and BOP 234. Such lines may be known by names such as “choke line”, “booster line”, “kill line”, etc., depending on the use of the individual line 200, 202.
In order to prevent the drilling fluid pressure from exceeding an acceptable level (e.g., in the case of gas influx into the well), the drilling riser 212 may be provided with a gas handler. An example embodiment of a gas handler is described in U.S. Pat. No. 8,413,724 issued to Carbaugh et al.
While the example embodiment shown in
A riser gas handling/managed pressure drilling control system skid (“control skid”) 422 may be disposed on the drilling platform (204 in
Fluid flow from below and above the components of the subsea wellhead 234 may be communicated through flow lines (in some embodiments clamped onto the exterior of the riser (212 in
A pressure relief valve or pressure control valve 416 may be in fluid communication with the distribution manifold 414. In the event of excessive pressure in any part of the distribution manifold, the pressure relief valve 416 may open to vent the excess pressure. Output of the rig mud pumps may be directed to a standpipe manifold 420 in fluid communication with the distribution manifold. A choke manifold 418 having one or more chokes, including in some embodiments controllable orifice chokes may be in fluid communication between the standpipe manifold 420 and the distribution manifold 414, for example, to implement a backpressure system as described with reference to
A managed pressure drilling/riser gas handling choke (MPD/RGH) manifold 422 may be in fluid communication with the distribution manifold 414 to implement managed pressure drilling or riser gas abatement as drilling conditions may require. The MPD/RGH manifold 422 may also have a PRV 438 in fluid communication therewith to vent fluid in the event pressure in the MPD/RGH manifold 428 exceeds a safe amount.
Drilling fluid return processing components may comprise a rig flow system 434, a flowmeter 440 and mud gas separator 442.
Operating logic 430, which may be stored in a non-transitory computer-readable storage medium may be used to cause a processor, which may be disposed in the control system skid 422, to implement drilling fluid pressure and flow control as will now be explained with reference to
In
When the drilling system operator decides to use managed pressure drilling, an RCD and fluid outlet components may be assembled onto the well, as shown at 511, as explained with reference to
When it is determined from various sensor measurements that fluid is neither entering the well from a formation nor is drilling fluid being lost to any formation, at 500, discharge of returned fluid from the well is directed to the MPD/RGH manifold at 502, and then to the controllable orifice choke at 504 so that selected fluid pressure may be maintained in the well. Fluid leaving the controllable orifice choke (e.g., 130 in
At 514, if a fluid influx into the well is detected, for example and without limitation, measurement of an increase in flow rate of fluid being discharged from the well while the rate of pumping drilling fluid into the well is unchanged, or measurement of a position of a control that operates the controllable orifice choke as described in U.S. Pat. No. 7,562,723 issued to Reitsma. In such event, the MPD/RGH system may automatically change to “riser gas handling” (RGH) mode at 516. In RGH mode, the annular BOP (408 in
If the fluid influx continues, at 521, returned drilling fluid may continue to be processed through the mud gas separator, at 522. Drilling fluid that has had gas removed therefrom may be returned to the fluid flow system at 508.
At 523, the volume of gas that is extracted from the returned fluid is monitored. If the gas volume remains below a selected volume limit, drilling in RGH mode may continue. If the selected volume limit is exceeded, at 523, excess gas may be vented at 527 or otherwise disposed of (e.g., by flaring). The well fluid flow system may remain in RGH mode (return to 516 in
If measurements of fluid flow into the well and fluid flow out of the well indicate that drilling fluid is being lost into a subsurface formation, at 528, the MPD/RGH system (e.g., as determined in the control system skid (422 in
A system and method according to the present disclosure may provide more effective and rapid control over fluid influx and fluid loss events during well drilling.
While the disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of what has been described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.