SUBSEA FLUID PROCESSING SYSTEM WITH INTERMEDIATE RE-CIRCULATION

Abstract

A fluid processing system is provided containing a pump and a fluid reservoir. The pump includes a casing, one or more pump stages, a pump inlet, and a pump outlet. The casing includes one or more slots, with at least one slot configured to extract at least a portion of a multiphase fluid flowing within the pump. The fluid reservoir encompasses at least a portion of the casing and is configured to receive and separate the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase. The fluid reservoir includes a re-circulation conduit disposed proximate to the pump inlet and a discharge device coupled to the re-circulation conduit. The discharge device regulates re-circulation of at least a portion of the extracted liquid phase to the pump via the pump inlet for reducing a gas volume fraction of the multiphase fluid being fed to the pump.

Description

BACKGROUND

The present invention relates to fluid processing systems for deployment in a subsea environment, and more particularly to subsea systems capable of handling production fluids characterized by high gas volume fraction (GVF).

Fluid processing systems used for hydrocarbon production in subsea environments typically include pumps configured to boost production fluids from a subsea hydrocarbon reservoir to a distant storage facility. Such pumps are typically designed to operate with production fluids having relatively low gas volume fraction (GVF).

Generally, gas slugs occur due to flow instability of multiple phases of the production fluids. Such flow instability may occur in pipelines deployed for moving the production fluids. Eventually, these gas slugs may enter the fluid processing systems and may cause rapid change in the GVF to higher values. Pumps receiving such production fluids with high GVF may be damaged thereby.

To protect the pumps from incoming gas slugs, a portion of a liquid phase of the production fluid may be re-circulated from a downstream separator to the inlet tank, where the liquid phase is mixed with the incoming production fluid before being fed to a pump. However, such re-circulation of the liquid phase may result in overall pressure losses to the system as the liquid phase at high pressure needs to be throttled to lower pressure before being fed to the inlet tank. Further, when the pressure is lowered the liquid phase may tend to flash (i.e. convert from a liquid phase to a gaseous phase) which may reduce efficiency.

Thus, there is a need for an improved fluid processing system for efficiently handling production fluids characterized by high gas volume fraction (GVF) and to regulate the GVF of a production fluid being fed to a processing system pump.

BRIEF DESCRIPTION

In one embodiment, the present invention provides a fluid processing system comprising: (a) a pump including a casing, one or more pump stages, a pump inlet, and a pump outlet, the casing defining one or more slots, wherein at least one of the slots is configured to extract at least a portion of a multiphase fluid flowing within the pump, and wherein each pump stage comprises a diffuser and an impeller; and (b) a fluid reservoir encompassing at least a portion of the casing and configured to receive and separate the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase, wherein the fluid reservoir comprises a re-circulation conduit disposed proximate to the pump inlet, and a discharge device coupled to the re-circulation conduit and configured to regulate re-circulation of at least a portion of the extracted liquid phase to the pump via the pump inlet so as to reduce a gas volume fraction (GVF) of the multiphase fluid being fed to the pump.

In another embodiment, the present invention provides a method for reducing a gas volume fraction of a production fluid comprising: (a) introducing a multiphase fluid into a pump configured to increase pressure of the multiphase fluid, wherein the pump comprises a casing, one or more pump stages, a pump inlet, and a pump outlet, wherein each pump stage comprises a diffuser and an impeller; (b) extracting at least a portion of the multiphase fluid flowing within the pump into a fluid reservoir encompassing at least a portion of the casing via one or more slots defined in the casing, wherein the fluid reservoir comprises a re-circulation conduit disposed proximate to the pump inlet and a discharge device coupled to the re-circulation conduit; (c) separating the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase; (d) re-circulating at least a portion of the extracted liquid phase through the re-circulation conduit into the pump via the pump inlet by regulating a flow of the extracted liquid phase via the discharge device; and (e) mixing the extracted liquid phase with the multiphase fluid at the pump inlet so as to reduce the gas volume fraction (GVF) of the multiphase fluid being fed to the pump.

In another embodiment, the present invention provides a method of transporting a production fluid comprising: (a) receiving a first production fluid in an inlet tank and mixing it with a primer liquid to produce thereby a second production fluid (multiphase fluid) having a reduced gas volume fraction (GVF) relative to the first production fluid; (b) introducing the multiphase fluid from the inlet tank into a pump configured to increase pressure of the multiphase fluid and produce thereby a compressed multiphase fluid, wherein the pump comprises a casing, one or more pump stages, a pump inlet, and a pump outlet, and wherein each pump stage comprises a diffuser and an impeller; (c) extracting at least a portion of the multiphase fluid flowing within the pump into a fluid reservoir encompassing at least a portion of the casing via one or more slots defined in the casing, wherein the fluid reservoir comprises a re-circulation conduit disposed proximate to the pump inlet and a discharge device coupled to the re-circulation conduit; (d) separating the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase; (e) re-circulating at least a portion of the extracted liquid phase through the re-circulation conduit into the pump via the pump inlet by regulating a flow of the extracted liquid phase via the discharge device; (f) mixing the extracted liquid phase with the multiphase fluid at the pump inlet to further reduce the GVF of the multiphase fluid being fed to the pump; and (g) transporting the compressed multiphase fluid from the pump to a fluid storage facility via a fluid conduit.

DRAWINGS

These and other features and aspects of embodiments of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a subsea system in accordance to an embodiment of the invention;

FIG. 2 illustrates a fluid processing system in accordance to an embodiment of the invention;

FIG. 3 illustrates a fluid processing system in accordance to another embodiment of the invention;

FIG. 4 illustrates a pump and a fluid reservoir in accordance to an embodiment of the invention;

FIG. 5 illustrates a pump and a fluid reservoir in accordance to another embodiment of the invention;

FIG. 6 illustrates a portion of a pump in accordance to an embodiment of the invention;

FIG. 7 illustrates a portion of a pump in accordance to another embodiment of the invention;

FIG. 8 illustrates a portion of a pump in accordance to yet another embodiment of the invention;

FIG. 9 illustrates a portion of a pump in accordance to yet another embodiment of the invention;

FIG. 10 illustrates a portion of a pump in accordance to yet another embodiment of the invention;

FIG. 11 illustrates a portion of a pump in accordance to yet another embodiment of the invention;

FIG. 12 illustrates a portion of a fluid processing system in accordance to an embodiment of the invention;

FIG. 13 illustrates a portion of a fluid processing system in accordance to another embodiment of the invention;

FIG. 14 illustrates a portion of a subsea system in accordance to an embodiment of the invention;

FIG. 15 illustrates a portion of a fluid processing system in accordance to an embodiment of the invention; and

FIG. 16 illustrates a portion of a fluid processing system in accordance to another embodiment of the invention.

DETAILED DESCRIPTION

Embodiments discussed herein disclose new subsea systems for efficiently moving production fluids characterized by high gas volume fraction (GVF) from a hydrocarbon reservoir to a distant fluid storage facility. Specifically, the embodiments disclose an improved fluid processing system for effectively managing the GVF of the production fluids. The fluid processing system of the present invention comprises a pump and a fluid reservoir encompassing a portion of the pump. One or more slots defined in a casing of the pump, are configured to extract a portion of a multiphase fluid flowing in the pump at an intermediate pressure. The one or more slots may be defined in one or more regions of the casing and may have optimal shapes to facilitate extraction of a stagnant portion (flow) of the multiphase fluid without affecting a main flow of the multiphase fluid. A discharge device is coupled to a re-circulation conduit of the fluid reservoir. The discharge device may include one among a passive device and an active device to efficiently regulate the quantity of and the pressure at which a liquid phase of the multiphase fluid being fed to the pump for controlling the GVF of the production fluids. Suitable discharge devices include valves and one or more cylinders comprising at least one hole or opening.

FIG. 1 represents a subsea system 100 for handling production fluids deployed in a subsea environment 102 proximate to a hydrocarbon reservoir 104. The hydrocarbon reservoir 104 may produce a production fluid comprising oil, water, and gas. In certain embodiments, the hydrocarbon reservoir 104 may produce a production fluid comprising a dry gas or crude oil and dry gas.

The subsea system 100 includes an inlet tank 106, a fluid processing system 108, a fluid re-circulation loop 110, and a fluid outlet 112. The subsea system 100 further includes a fluid inlet 114 in fluid communication with the inlet tank 106 coupled to the hydrocarbon reservoir 104, and a feed line 118 linking the fluid processing system 108 to the inlet tank 106. In certain other embodiments, the fluid inlet 114 may include a well-head valve (not shown in FIG. 1) for regulating a flow of a first production fluid stream 120 (i.e. production fluid) from the hydrocarbon reservoir 104. The inlet tank 106 is configured to receive the production fluid stream 120 from the hydrocarbon reservoir 104 and a primer liquid stream 123 from a pump outlet 124 of the fluid processing system 108 via the fluid re-circulation loop 110. In one or more embodiments, the pump outlet 124 includes a liquid-gas separator (not shown in FIG. 1) configured to separate the primer liquid 123 from a compressed multiphase fluid 122. The primer liquid stream 123 may be comprised of a liquid stream of the compressed multiphase fluid 122. The inlet tank 106 is configured to mix the production fluid stream 120 and primer liquid stream 123 to produce thereby a second production fluid stream 126 (i.e. multiphase fluid) having a reduced gas volume fraction (GVF) relative to the production fluid 120. In one or more embodiments, the primer liquid 123 may include one or more liquids separated from the multiphase production fluid 126 such as water and crude oil. In alternative embodiment, the primer liquid 123 may comprise an exogenous liquid such as a solvent (e.g. ethanol) or other liquid not derived from the multiphase production fluid 126.

The fluid processing system 108 includes a pump 128 and a fluid reservoir 130 encompassing at least a portion of the pump 128. The pump 128 has a pump inlet 132, the pump outlet 124, and one or more slots 134 defined in a casing 158 of the pump. The pump inlet 132 is fluidly coupled to the inlet tank 106 and the pump outlet 124 is fluidly coupled to both the inlet tank 106 and to a distant storage facility 138. In the embodiment shown, the fluid-recirculation loop 110 has a flow-control valve 136 configured to regulate a flow of the primer liquid stream 123 into the inlet tank 106. In certain other embodiments, the system 100 may include a plurality of pumps 128 coupled in a parallel configuration or in a serial configuration. The fluid reservoir 130 has a re-circulation conduit 140 disposed proximate to the pump inlet 132, a re-injection conduit 142 disposed proximate to the one or more slots 134, and a discharge device 144 coupled to the re-circulation conduit 140. Pump 128 and fluid reservoir 130 are discussed in greater detail below.

The system 100 further includes a pipe 116 disposed between the fluid inlet 114 and distant storage facility 138. The pipe 116 has a by-pass valve 154 configured to regulate a flow of the production fluid stream 120 from the hydrocarbon reservoir 104 to the distant storage facility 138 based on one or more pre-determined conditions. In one or more embodiments, the one or more pre-determined conditions may include start-up, shutdown, and maintenance of the subsea system 100.

During operation inlet tank 106 receives and mixes the production fluid stream 120 from the hydrocarbon reservoir 104 with the primer liquid stream 123 from the pump outlet 124 to produce the multiphase fluid 126 having a reduced GVF relative to the production fluid 120. The production fluid stream 120 may include gas slugs 156 which, as noted, may harm system components or affect efficiency. The multiphase fluid 126 is then fed to the fluid processing system 108.

The pump 128 receives the multiphase fluid stream 126 and increases its pressure. A portion of the multiphase fluid stream 126 flowing within the pump 128 at an intermediate pressure is extracted into the fluid reservoir 130 via the one or more slots 134.

In the fluid reservoir 130 the extracted portion of the multiphase fluid 126 settles down and phase separates into an extracted liquid phase 146 and extracted gaseous phase 148. In one or more embodiments, the fluid reservoir 130 itself is configured as a liquid-gas separator. In other embodiments, the fluid reservoir 130 may include a discrete liquid-gas separator. In such embodiments, the liquid-gas separator receives the extracted portion of the multiphase fluid 126 and separates the liquid phase from gaseous phase using, for example, a barrier, a filter, or a vortex flow separator. In one or more embodiments, a suitable liquid-gas separator may include one or more weir separators, filter separators, cyclone separators, sheet metal separators, or a combination of two or more of the foregoing separators.

A portion of the extracted liquid phase 146 is re-circulated as indicated by a reference numeral 150, into the pump inlet 132 through the re-circulation conduit 140. In one or more embodiments, the re-circulation of the extracted liquid phase 146 into the pump inlet 132 is referred as an intermediate re-circulation. The discharge device 144 regulates the flow of the extracted liquid phase 146 into the pump inlet 132 where it is mixed with multiphase fluid 126 to further reduce the GVF of the multiphase fluid 126 being fed to the pump 128. The extracted gaseous phase 148 is re-injected as indicated by reference numeral 152, to the pump 128 through re-injection conduit 142. The re-injection conduit 142 is shown as configured to deliver the gaseous phase 148 upstream of the one or more slots 134. As noted pump 128 produces the compressed multiphase fluid 122, a portion of which may be separated for use as the primer liquid 123.

In one or more embodiments, the subsea system 100 may include a plurality of sensors (not shown in FIG. 1) coupled to an electronic control unit (not shown in FIG. 1) for regulating the flow of the primer liquid stream 123 and/or the extracted liquid phase 146 and/or the production fluid stream 120. The plurality of sensors may include one or more liquid-level indicators, flow meters, and speed sensors. The electronic control unit typically includes at least one data processor. The plurality of sensors may be configured to generate a plurality of input signals based on a plurality of sensed parameters of the subsea system 100. The electronic control unit may be configured to generate one or more control signals based on the plurality of input signals.

In one embodiment, the electronic control unit generates a control signal to regulate feeding of the primer liquid stream 123 to the inlet tank 106 via the flow control valve 136. The control unit may generate a control signal to regulate intermediate re-circulation of the portion of extracted liquid phase 146 into the pump inlet 132 via the discharge device 144. The electronic control unit may be configured to regulate feeding of the production fluid stream 120 to the distant storage facility 138 via the by-pass valve 154.

FIG. 2 represents a fluid processing system 108 in accordance with an exemplary embodiment. The fluid processing system 108 includes a pump 128 and a fluid reservoir 130. In the embodiments shown, the fluid reservoir 130 is an integral component of the pump 128. In certain other embodiments, the fluid reservoir 130 may be a discrete component which may be fluidly coupled to the pump 128 via pipes.

Pump 128 has a shaft 160 disposed at least partially within a casing 158 and coupled to a motor (not shown in FIG. 2), and one or more pump stages 162. Each pump stage 162 has an impeller 164 and a diffuser 166. The pump 128 has one or more slots 134 such as through-holes, defined in the casing 158. The one or more slots 134 are located proximate to a pump inlet 132. In the embodiment shown, the one or more slots 134 are located after a second pump stage 162b from the pump inlet 132. Each slot 134 is positioned at about 20 percent to about 80 percent of a length “L” of the diffuser 166. In one or more embodiments, suitable pumps include rotary pumps, centrifugal pumps, and reciprocating pumps.

The re-injection conduit 142 is disposed between a first opening 174 formed in a top portion 170 of the fluid reservoir 130 and a second opening 176 formed in the casing 158. The re-circulation conduit 140 has an opening 178 disposed proximate to the pump inlet 132. The opening 178 is located at a bottom portion 172 of the fluid reservoir 130. The re-circulation conduit 140 further includes the discharge device 144 disposed at the opening 178. The one or more slots 134 and the discharge device 144 are discussed in greater detail below.

During operation multiphase fluid 126 is compressed at each pump stage 162 via the impeller 164 and guided to a subsequent pump stage 162 via the diffuser 166. The one or more slots 134 extract a portion of the multiphase fluid 126 at an intermediate pressure from the pump 128. In the illustrated embodiment, the extraction of the multiphase fluid 126 is indicated by a reference numeral 180. The extracted multiphase fluid 126 is separated into liquid phase and gaseous phase. As dictated by gravity, the extracted liquid phase 146 is stored at the bottom portion 172 of the fluid reservoir 130 and the extracted gaseous phase 148 is stored at the top portion 170 of the fluid reservoir 130. The extracted gaseous phase 148 is re-injected to the pump 128 through the re-injection conduit 142 wherein a portion of the extracted liquid phase 146 is re-circulated to the pump 128 through the re-circulation conduit 140. The discharge device 144 regulates the flow of the extracted liquid phase 146. In one or more embodiments, the re-circulation may depend on the GVF at the pump inlet 132.

FIG. 3 represents a fluid processing system 108 in accordance with another exemplary embodiment. The illustrated embodiment does not include a separate re-injection conduit 142 as shown in the embodiment of FIG. 2. One or more slots 134 defined in the casing 158 is configured for both extraction (as indicated by reference numeral 180) of the multiphase fluid 126 from the pump 128 and re-injection (as indicated by reference numeral 152) of the extracted gaseous phase 148 into the pump 128. The extraction and re-injection may happen at the same pump stage 162.

FIG. 4 represents a fluid processing system 108 comprising a pump 128 and a fluid reservoir 130 in accordance with an exemplary embodiment. The pump 128 includes a first pump inlet 182 and a first pump outlet 184. The pump 128 has a first set of pump stages 162a and a second set of pump stages 162b disposed within a casing 158. The first set of pump stages 162a is disposed between a pump inlet 132 and the first pump outlet 184. The second set of pump stages 162b is disposed between the first pump inlet 182 and a pump outlet 124. The first pump inlet 184 and first pump outlet 182 are fluidly coupled to each other via a conduit 186. The first and second set of pump stages 162a and 162b are in a serial configuration. The casing 158 further includes one or more slots 134 disposed upstream relative to the first pump outlet 184. The fluid reservoir 130 encompasses the portion of the casing 158 defining the first set of pump stages 162a.

During operation multiphase fluid 126 enters the first set of pump stages 162a where it is compressed to a first pressure. A portion of the multiphase fluid 126 at the first pressure is extracted through the one or more slots 134 into the fluid reservoir 130, as discussed earlier. In one or more embodiments, the first pressure may be an intermediate pressure. A remaining portion of the multiphase fluid 126 substantially above the first pressure exits the first set of pump stages 162a through the first pump outlet 184 and flows in the conduit 186 before being fed to the second set of pump stages 162b via the first pump inlet 182. The multiphase fluid 126 is then compressed along the second set of pump stages 162b to generate the compressed multiphase fluid 122 at a second pressure. The pump outlet 124 discharges the compressed multiphase fluid 122 from the pump 128.

FIG. 5 represents a fluid processing system 108 comprising a pump 128 and a fluid reservoir 130 in accordance with an exemplary embodiment. The pump 128 includes a first pump inlet 132a disposed at a first end 188 of the pump 128 and a second pump inlet 132b disposed at a second end 190 opposite to the first end 188, of the pump 128. The pump 128 has a first set of pump stages 162a and a second set of pump stages 162b disposed within a casing 158. The first and second set of pump stages 162a and 162b are in a parallel configuration. The pump outlet 124 is disposed at an exit section of the first and second set of pump stages 162a and 162b. The fluid reservoir 130 encompasses the portion of the casing 158 defining the first set of pump stages 162a. The bottom portion 172 of the fluid reservoir 130 further includes a liquid conduit 192 fluidly coupled to the second fluid inlet 132b. The liquid conduit 192 includes a control valve 194. The top portion 170 of the fluid reservoir 130 includes a gaseous conduit 196 fluidly coupled to a portion of the casing 158 corresponding to the second set of pump stages 162b.

During operation multiphase fluid 126 enters the first and second set of pump stages 162a and 162b of the pump 128. The multiphase fluid 126 is compressed along the one or more stages of the first and second set of pump stages 162a and 162b. A portion of the multiphase fluid 126 flowing along the first set of pump stages 162a is extracted into the fluid reservoir 130 through one or more slots 134 as discussed earlier. A remaining portion of the multiphase fluid 126 flowing along the first set of pump stages 162a and the multiphase fluid 126 flowing along the second set of pump stages 162b are compressed to generate the compressed multiphase fluid 122. The pump outlet 124 discharges the compressed multiphase fluid 122 from the pump 128. In the embodiment shown, a portion of the extracted liquid phase 146 is fed from the fluid reservoir 130 into the second pump inlet 132b via the liquid conduit 192. The control valve 194 may regulate a flow of the portion of the extracted liquid phase 146. Further, a portion of the extracted gaseous phase 148 may be fed from the fluid reservoir 130 into the second set of pump stages 162b via the gaseous conduit 196.

FIG. 6 represents a portion 197 of a pump 128 in accordance with an exemplary embodiment. The portion 197 has a plurality of diffusers 166 and a slot 134 defined in a casing 158. The slot 134 is positioned corresponding to a mid-length of the plurality of diffusers 166 and has a width “W₁”. Further, the slot 134 is a continuous slot having a uniform size along the casing 158. In certain other embodiments, the slot 134 may be positioned anywhere between a leading edge 204 and a trailing edge 206 of the plurality of diffusers 166. Specifically, the slot 134 may be positioned at about 20 percent to about 80 percent of the length “L” of the plurality of diffusers 166. The slot 134 may be configured to extract a portion of the multiphase fluid 126 from the pump 128 and to re-inject an extracted gaseous phase 148 into the pump 128.

FIG. 7 represents a portion 199 of a pump 128 in accordance with another exemplary embodiment. In the illustrated embodiment, a slot 134 defined in a casing 158 has a width “W₂” different than the width “W₁” as shown in the embodiment of FIG. 6. The slot 134 having a smaller width may accurately regulate a quantity of a multiphase fluid 126 extracted into the fluid reservoir 130. Similar to the embodiment of FIG. 6, the slot 134 is a continuous slot having a uniform size along the casing 158 and is positioned at a mid-length of a plurality of diffusers 166.

FIG. 8 represents a portion 201 of a pump 128 in accordance with yet another exemplary embodiment. A slot 134 is located proximate to a leading edge 204 of a plurality of diffusers 166. Similar to the embodiment of FIG. 6, the slot 134 is a continuous slot having a uniform size along a casing 158. FIG. 9 represents a portion 203 of a pump 128 in accordance with yet another exemplary embodiment. A slot 134 is located proximate to a trailing edge 206 of a plurality of diffusers 166. Similar to the embodiment of FIG. 6, the slot 134 is a continuous slot having a uniform size along a casing 158.

FIG. 10 represents a portion of 205 of a pump 128 in accordance with yet another exemplary embodiment. The portion 205 has one or more discrete slots 134 defined in a casing 158. In the illustrated embodiment, each slot 134 is positioned corresponding to a mid-length of a plurality of diffusers 166. Further, each slot 134 has a width “W₁” and covers a portion of a pressure side 202 and a suction side 200 of at least one diffuser 166. As shown in the embodiments of FIGS. 6, 7, 8, and 9, each slot 134 may have different width and may be positioned anywhere between a leading edge 204 and a trailing edge 206 of the plurality of diffusers 166.

FIG. 11 represents a portion of 207 of a pump 128 in accordance with yet another exemplary embodiment. The portion 207 includes one or more discrete slots 134 defined in a casing 158. In one embodiment, each slot 134 is positioned proximate to a trailing edge 206. Each slot 134 has a non-uniform size along the casing 158 and is disposed between a suction side 200 of a diffuser 166 and a pressure side 202 of a mutually adjacent diffuser 166. The shape and position of each slot 134 may be chosen such that an extraction of the multiphase fluid 126 happens from an area of the diffuser 166 where the multiphase fluid 126 tends to re-circulate (or have more turbulence or is a stagnant flow) within the pump 128. Each slot 134 removes the stagnant flow (i.e. low quality flow) from such area of the diffuser 166 to improvise an aero dynamic effect of the multiphase fluid 126 within the pump 128.

FIG. 12 represents a portion 208 of a fluid processing system 108 in accordance with an exemplary embodiment. The portion 208 illustrates a discharge device 144 in accordance to the exemplary embodiment.

The discharge device 144 is an active device including a plurality of concentric cylinders 210 disposed at an opening 178 of the re-circulation conduit 140. An outer concentric cylinder 210a among the plurality of concentric cylinders 210 has a side wall 212 rotatably engaged with an outer wall 214 of the re-circulation conduit 140. Similarly, an inner concentric cylinder 210b among the plurality of concentric cylinders 210 has a side wall 216 coupled to a casing 158 of a pump 128. The side walls 212 and 216 are inclined at a pre-determined angle “a” relative to a wall 219 of a pump inlet 132. In one or more embodiments, the pre-determined angle “a” may be a negative angle, a positive angle, zero, or combination thereof depending on an application and design criteria. The plurality of concentric cylinders 210 is a hollow cylinder with each cylinder 210 having one or more holes 218 spaced apart from each other and disposed along a circumference of each cylinder 210. The outer concentric cylinder 210a is coupled to an actuator (not shown in FIG. 12) for rotating (as designated by a reference number 217) the cylinder 210a about an axis of the shaft 160. The inner concentric cylinder 210b is a stationary cylinder. In certain other embodiments, the outer concentric cylinder 210a may be stationary and the inner concentric cylinder 210b may be rotatable about the axis of the shaft 160.

During operation actuator may rotate the outer concentric cylinder 210a for aligning one or more holes 218a with one or more holes 218b of inner concentric cylinder 210b. Such alignment of holes 218a and 218b allows the extracted liquid phase 146 to flow through the discharge device 144 into the pump inlet 132. The outer concentric cylinder 210a may be regulated via the actuator by an electronic control unit as discussed in the embodiment of FIG. 1. The concentric cylinders 210 may control a pressure and a quantity of the extracted liquid phase 146 being re-circulated into the pump 128. In one or more embodiments, suitable actuators may include motors.

FIG. 13 represents a portion 209 of a fluid processing system 108 in accordance with another exemplary embodiment. The portion 209 illustrates a discharge device 144 in accordance to the exemplary embodiment. The discharge device 144 is an active device including a valve 220 disposed in a pipe 222 which is coupled between a re-circulation conduit 140 and a pump inlet 132. As discussed in the embodiment of FIG. 12, the valve 220 may be driven by an actuator to regulate intermediate re-circulation of an extracted liquid phase 146 into the pump inlet 132.

FIG. 14 represents a portion 211 of a subsea system 100 in accordance to an exemplary embodiment. The portion 211 illustrates a discharge device 144 and an actuator 225. The discharge device 144 is a passive device including a valve 224 disposed in a pipe 222 coupled to a re-circulation conduit 140 and a pump inlet 132. The actuator 225 is disposed in a conduit 232 coupled to a fluid outlet 112 and the pipe 222 via an opening 230. The actuator 225 is further coupled to the valve 224. In the embodiment shown, the actuator 225 is a first piston including a spring 234 disposed between a piston head (not labeled) and the opening 230.

During operation a portion of a compressed multiphase fluid 122 flows in the conduit 232 and a portion of an extracted liquid phase 146 flows in the pipe 222. The first piston 225 is configured to reciprocate along the opening 230 to either engage or disengage the valve 224 based on a pressure difference between the pipe 222 and conduit 232. For example, when a pressure applied by the compressed multiphase fluid 122 in the conduit 232 is significantly greater than a pressure applied by the extracted liquid phase 146 in the pipe 222, the first piston 225 engages the valve 224 and obstructs a flow of the extracted liquid phase 146 into the pump inlet 132. Similarly, when the pressure applied by the extracted liquid phase 146 in the pipe 222 is significantly greater than the pressure applied by the compressed multiphase fluid 122 in the conduit 232, the first piston 225 disengages the valve 224 and allows the flow of the liquid phase 146 into the pump inlet 132.

In certain embodiments, the conduit 232 may further include a second piston (not shown in FIG. 14) disposed at an opening 113 formed in the fluid outlet 112. In such embodiments, the conduit 232 may be filled with a fluid such as oil and water, different than the compressed fluid 112. The second piston may compress the fluid based on the pressure of the compressed multiphase fluid 122 flowing in the fluid outlet 112 and thereby increase the pressure across the first piston 225 to engage the valve 224.

FIG. 15 represents a portion 213 of a fluid processing system 108 in accordance with yet another exemplary embodiment. The portion 213 illustrates a discharge device 144 in accordance to the exemplary embodiment. The discharge device 144 is a passive device including a cylinder 236 disposed at an opening 178 of a re-circulation conduit 140. The cylinder 236 includes a side wall 240 coupled to a casing 158 and an outer wall 214 of a fluid reservoir 130. The side wall 240 is inclined at a pre-determined angle “a” relative to a wall 219 of a pump inlet 132. The cylinder 236 is a hollow cylinder with one or more holes 238 spaced apart from each other and disposed along a circumference of the cylinder 236. In the embodiment shown, the cylinder 236 is a stationary cylinder. During operation an extracted liquid phase 146 is re-circulated continuously from the re-circulation conduit 140 into the pump inlet 132 via the one or more holes 238.

In certain embodiments, the side wall 240 is inclined at a zero angle relative to the wall 219 i.e. the side wall 240 is disposed substantially parallel to the wall 219. In such embodiments, the cylinder 236 may move up and/or down via an actuator, to either open and/or close a portion of the holes 238 for selectively allowing the extracted liquid phase 146 to flow into the pump inlet 132.

FIG. 16 represents a portion 215 of a fluid processing system 108 in accordance with yet another exemplary embodiment. The portion 215 illustrates a discharge device 144 in accordance to the exemplary embodiment. The discharge device 144 is a passive device including a cylinder 242 disposed at an opening 178 of a fluid reservoir 130. The cylinder 242 includes a hole 244 such as a slit, defined along a circumference of the cylinder 242. In the illustrated embodiment, the hole 244 is substantially perpendicular relative to a wall 219 of a pump inlet 132. During operation an extracted liquid phase 146 is re-circulated from a re-circulation conduit 140 into the pump inlet 132 via the hole 244.

Similar to the embodiment discussed in FIG. 15, the cylinder 242 may move up and/or down via an actuator, to either open and/or close a portion of the slit 244 for selectively allowing the liquid phase 146 to flow into the pump inlet 132.

In accordance with certain embodiments discussed herein, a subsea system facilitates an efficient way of transporting a production fluid characterized by high gas volume fraction (gas slugs) from a subsea hydrocarbon reservoir to a distant storage facility. In doing so, the subsea system mixes a primer liquid with the production fluid primarily within an inlet tank to reduce a gas volume fraction (GVF) of the production fluid entering a pump and causing damage to the pump. Further, a fluid processing system of the present invention allows extraction of a portion of the multiphase fluid at an intermediate pressure from the pump, separation of a gaseous phase from a liquid phase, and intermediate re-circulation of the extracted liquid phase into the pump to further reduce the GVF of the multiphase fluid at the pump inlet thereby avoiding the further damage to the pump. The process of re-circulation of the primer liquid and the intermediate re-circulation of the extracted liquid phase may be automated by having a plurality of sensors and an electronic control unit.

While only certain features of embodiments have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended embodiments are intended to cover all such modifications and changes as falling within the spirit of the invention.

Claims

1. A fluid processing system comprising: a pump including a casing, one or more pump stages, a pump inlet, and a pump outlet, the casing defining one or more slots, wherein at least one of the slots is configured to extract at least a portion of a multiphase fluid flowing within the pump, wherein each pump stage comprises a diffuser and an impeller; anda fluid reservoir encompassing at least a portion of the casing and configured to receive and separate the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase,wherein the fluid reservoir comprises a re-circulation conduit disposed proximate to the pump inlet, and a discharge device coupled to the re-circulation conduit and configured to regulate re-circulation of at least a portion of the extracted liquid phase to the pump via the pump inlet so as to reduce a gas volume fraction (GVF) of the multiphase fluid being fed to the pump.

2. The system according to claim 1, wherein the fluid reservoir further comprises a re-injection conduit coupled to the one or more pump stages upstream relative to the slots and configured to regulate re-injection of the extracted gaseous phase into the pump.

3. The system according to claim 1, wherein the pump stages are arranged in a serial configuration.

4. The system according to claim 1, wherein the pump stages are arranged in a parallel configuration.

5. The system according to claim 1, wherein the one or more slots are located at about 20 percent to about 80 percent of a length of the diffuser.

6. The system according to claim 1, wherein the one or more slots comprises at least one of a continuous slot, a discrete slot, a non-uniform slot.

7. The system according to claim 6, wherein the one or more slots are positioned along at least one of a mid-chord length of the diffuser, a leading edge of the diffuser, and a trailing edge of the diffuser.

8. The system according to claim 1, wherein the discharge device comprises a plurality of concentric cylinders with each cylinder having one or more holes for allowing the extracted liquid phase to flow through the discharge device.

9. The system according to claim 8, wherein each cylinder comprises a side wall inclined at a pre-determined angle relative to the pump inlet, to regulate at least one a pressure and a quantity of extracted liquid phase being fed to the pump.

10. The system according to claim 1, wherein the discharge device comprises a valve disposed in a pipe coupled between the re-circulation conduit and the pump inlet, for regulating a flow of the extracted liquid phase into the pump.

11. The system according to claim 1, wherein the discharge device comprises a valve disposed in a pipe and coupled to an actuator disposed in a conduit, wherein the pipe is coupled to the re-circulation conduit and the pump inlet, and the conduit is coupled to the pipe and the fluid outlet, wherein the valve is configured to regulate a flow of the extracted liquid phase into the pump based on a pressure difference across the pump.

12. The system according to claim 1, wherein the discharge device comprises a cylinder including one or more holes for allowing the extracted liquid phase to flow into the pump inlet.

13. The system according to claim 1, wherein the discharge device comprises at least one of an active device and a passive device and configured to regulate a flow of the extracted liquid phase into the pump.

14. A method comprising: introducing a multiphase fluid into a pump configured to increase pressure of the multiphase fluid, wherein the pump comprises a casing, one or more pump stages, a pump inlet, and a pump outlet, wherein each pump stage comprises a diffuser and an impeller;extracting at least a portion of the multiphase fluid flowing within the pump into a fluid reservoir encompassing at least a portion of the casing via one or more slots defined in the casing, wherein the fluid reservoir comprises a re-circulation conduit disposed proximate to the pump inlet and a discharge device coupled to the re-circulation conduit;separating the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase;re-circulating at least a portion of the extracted liquid phase through the re-circulation conduit into the pump via the pump inlet by regulating a flow of the extracted liquid phase via the discharge device; andmixing the extracted liquid phase with the multiphase fluid at the pump inlet so as to reduce the gas volume fraction (GVF) of the multiphase fluid being fed to the pump.

15. The method of claim 14, further comprising re-injecting the extracted gaseous phase into the one or more pump stages upstream relative to the slots via the re-injection conduit coupled to the fluid reservoir.

16. The method of claim 14, wherein the regulating comprises controlling the discharge device having a plurality of concentric cylinders and one or more holes disposed on each cylinder, for allowing a flow of the extracted liquid phase into the pump.

17. The method of claim 14, wherein the regulating comprises controlling the discharge device having a valve disposed in a pipe coupled between the re-circulation conduit and the pump inlet, for allowing a flow of the extracted liquid phase into the pump.

18. The method of claim 14, wherein the regulating comprises controlling the discharge device having a valve coupled to an actuator, for allowing a flow of the extracted liquid phase into the pump based on a pressure difference across the pump, wherein the valve is disposed in a pipe and the actuator is disposed in a conduit, wherein the pipe is coupled to the re-circulation conduit and the pump inlet, and the conduit is coupled to the pipe and the fluid outlet.

19. A method comprising: receiving a first production fluid in an inlet tank and mixing it with a primer liquid to produce thereby a second production fluid (multiphase fluid) having a reduced gas volume fraction (GVF) relative to the first production fluid;introducing the multiphase fluid from the inlet tank into a pump configured to increase pressure of the multiphase fluid and produce thereby a compressed multiphase fluid, wherein the pump comprises a casing, one or more pump stages, a pump inlet, and a pump outlet, wherein each pump stage comprises a diffuser and an impeller;extracting at least a portion of the multiphase fluid flowing within the pump into a fluid reservoir encompassing at least a portion of the casing via one or more slots defined in the casing, wherein the fluid reservoir comprises a re-circulation conduit disposed proximate to the pump inlet and a discharge device coupled to the re-circulation conduit;separating the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase;re-circulating at least a portion of the extracted liquid phase through the re-circulation conduit into the pump via the pump inlet by regulating a flow of the extracted liquid phase via the discharge device;mixing the extracted liquid phase with the multiphase fluid at the pump inlet to further reduce the GVF of the multiphase fluid being fed to the pump; andtransporting the compressed multiphase fluid from the pump to a fluid storage facility via a fluid conduit.

20. The method according to claim 19, further comprising re-injecting the extracted gaseous phase into the one or more pump stages upstream relative to the one or more slots via the re-injection conduit coupled to the fluid reservoir.

21. The method according to claim 19, wherein the primer liquid comprises a liquid stream of the compressed multiphase fluid, which is delivered to the inlet tank via a re-circulation loop coupled to the fluid conduit, wherein the re-circulation loop comprises a control valve configured to regulate a flow of the liquid stream.