Patent Application
20210246771
In the oil and gas industry, Electric Submersible Pumps (ESPs) are widely used for extracting underground gas and liquid. More specifically, configurations with dual ESPs are common practice, especially when flows rates from a well need to be increased or additional pressure boost is required. Configurations with dual ESPs are also common when some level of redundancy is required. To operate these ESPs simultaneously, each ESP is connected to its own dedicated electric cable which separately delivers power from a power source on the surface to the downhole ESP. At the surface, the power cables are connected to their own Variable Frequency Drives (VFDs) to control each ESP independently.
An ESP system generally includes, among other elements, a centrifugal pump, a protector, an electric cable, a motor, and a sensor such as a monitoring sub/tool. The pump is used to lift well-fluids to the surface or, if at surface, transfer fluid from one location to another. The motor provides the mechanical power required to drive the pump via a shaft. The electric cable provides a means of supplying the motor with the needed electrical power from the surface. The protector absorbs the thrust load from the pump, transmits power from the motor to the pump, equalizes pressure, provides and receives additional motor oil as temperature changes and prevents well-fluid from entering the motor. The pump consists of stages, which are made up of impellers and diffusers. The impeller, which is rotating, adds energy to the fluid to provide kinetic energy, whereas the diffuser, which is stationary, converts the kinetic energy of fluid from the impeller into pressure head. The pump stages are typically stacked in series to form a multi-stage system that is contained within a pump housing. The sum of head generated by each individual stage is summative; hence, the total head developed by the multi-stage system increases linearly from the first to the last stage. The monitoring sub/tool is installed onto the motor to measure parameters such as pump intake and discharge pressures, motor oil and winding temperature, and vibration. Measured downhole data is communicated to the surface via the electric cable.
Dual ESP configurations are common in production operations. Such systems tend to be used when some redundancy is required to operate each ESP separately. The overall economic objective is to reduce the cost of working over a well. This is typically the case for offshore operations or in locations, where the cost of workover is extremely high. In the event that one ESP fails, the other can still be operated to ensure production continues.
The present disclosure relates to a pumping system for pumping downhole fluid.
The pumping system includes: a first electric submersible pump (ESP) and a second ESP, each of the first ESP and the second ESP including a motor, a pump inlet, and a pump outlet; a tubing fluidly coupled to the pump outlet of the first ESP and the pump outlet of the second ESP; a connector coupled to the first ESP; an electric cable coupled between an uphole power source and the connector to deliver electric power to the motor of the first ESP; and an electric cable extension coupled between the connector and the second ESP to deliver electric power to the motor of the second ESP.
In one aspect, the first ESP and the second ESP are fluidly coupled to the tubing in parallel such that the downhole fluid independently enters and exits the first ESP and the second ESP.
In another aspect, the first ESP and the second ESP are fluidly coupled to the tubing in series such that the pump outlet of the second ESP is in fluid communication with the pump inlet of the first ESP.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.
Specific embodiments of the present disclosure will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency. Like elements may not be labeled in all figures for the sake of simplicity.
Numerous specific details are set forth in the following detailed description in order to provide a more thorough understanding of the embodiments of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.
Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as an adjective for an element (i.e., any noun in the application). The use of ordinal numbers does not imply or create a particular ordering of the elements or limit any element to being only a single element unless expressly disclosed, such as by the use of the terms “before,” “after,” “single,” and other such terminology. Rather, the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements.
In the following description of
It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a horizontal beam” includes reference to one or more of such beams.
Terms such as “approximately,” “substantially,” etc., mean that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
Although multiple dependent claims are not introduced, it would be apparent to one of ordinary skill that the subject matter of the dependent claims of one or more embodiments may be combined with other dependent claims.
In conventional configurations where each ESP is driven by its own cable separately and the ESPs are operated simultaneously, additional design considerations may be contemplated to provide the required production or pressure boost. One consideration is the material/equipment quantity and associated cost as a result of running two reels of cable from the surface to the ESPs downhole. Such costs can be significantly higher, especially when the ESPs are set very deep in the well. Other operational problems related to running two cables in the casing may be experienced in slimmer casings, where clearance issues are prominent. These clearance issues can result in cables getting damaged when running in hole during the ESP installation process. With two power cables from the surface to operate both ESPs, two Variable Frequency Drives (VFDs) are required to provide the required speed control to operate the upper and lower ESPs. This results in having a larger surface footprint dedicated to running the ESPs, which can be a challenge for example in offshore operations, where space is a premium.
Further, because the two power cables have to pass through the packer, a cable splice may be needed above and below the packer to ensure proper termination of the power cables for electrical continuity. Increasing the number of splices increases the potential for electrical failure. This is especially the case in wells with corrosive gases such as H25 and for splice locations below the packer. The corrosive gas tends to accumulate just below the packer and, due to the high concentration of the gas in this region, the electrical splices are highly susceptible to attack by the gas. This can lead to gas ingress and potential failure of the ESP system. The above limitations show that a more economical method of operation is needed to ensure the shortcomings of current practices are prevented or at least, mitigated, to provide benefit to the field operator.
In general, embodiments disclosed herein relate to an artificial lift system that includes two pumps, wherein the two pumps may be operated simultaneously using a single power cable from the surface. For example, embodiments disclosed herein provide an artificial lift system comprising two ESPs that are operated using a single power cable extending from the surface. In other embodiments, the artificial lift system may include two progressive cavity pumps (PCPs) that are operated using a single power cable. The two pumps of the artificial lift system may be arranged in series or in parallel to provide the necessary pressure boost. Example embodiments are disclosed below including a dual ESP artificial lift system. However, one of ordinary skill in the art will appreciate that these configuration are equally applicable to other artificial lift devices, such as PCPs.
Two configurations of the dual ESP set-up are common: parallel configuration and series configuration. Embodiments having these configurations are described in
The upper ESP 140 may include a pump inlet 141, a pump outlet 142, a pump body 143, a protector 144, and a motor 145. The motor 145 may further include a sensor 146 such as a monitoring sub/tool. Similarly, the lower ESP 150 may include a pump inlet 151, a pump outlet 152, a pump body 153, a protector 154, and a motor 155. The motor 155 may further include a sensor 156 such as a monitoring sub/tool. One of ordinary skill in the art would understand that the elements shown in the figure are only for the purpose of illustration and do not limit the arrangement or structure of these elements. One of ordinary skill in the art would also understand that other structural or functional elements may also be present in each of ESP 140 and ESP 150. Further, one of ordinary skill in the art would understand that ESP 140 and ESP 150 may have the same structures or may have different structures.
When the upper ESP 140 and the lower ESP 150 are in operation, they generate a pressure difference between inside the pump and outside the pump such that fluids around the upper ESP 140 and the lower ESP 150 may flow inwards into pump bodies 143 and 153 through pump inlets 141 and 151, respectively. The pressure difference may further drive the fluids outwards through pump outlets 142 and 152 which are fluidly coupled to the tubing 102. The general principle of pumping operation is well-known in the art and is not described in detail herein.
As shown in
Y-tool 147 and 157 may provide access to bypass the upper ESP 140 and the lower ESP 150 during stimulation and logging, etc. A Y-tool is a component that may be installed on production tubing to provide two separate conduits. A first conduit of the Y-tool is concentric with the tubing 102 and provides access to the reservoir below the ESP, and a second conduit (a bypass leg) of the Y-tool is offset and is coupled to and supports the ESP. To produce well fluid to the surface in this configuration, a plug 158 may be set in the first conduit of the Y-tool 157 of the lower ESP 150. When both ESPs 140 and 150 are turned on, well fluid may flow into the inlet 151 of the lower ESP 150, and the fluid may be pressurized and flow into the Y-tool 157. Because a plug 158 is disposed in the first conduit, the pressurized fluid may flow up the bypass tubing 112. A similar scenario may occur for the upper ESP 140 during production. Since there is higher pressure fluid from the lower ESP 150 flowing up the bypass tubing 112, the pressurized fluid from the upper ESP 140 does not flow down the bypass tubing 112, but instead flows upwards towards the production tubing 122. The combined flows from the ESPs 140 and 150 may commingle just above the Y-tool 147 of the upper ESP 140 and are produced to the surface via the production tubing 122.
Still referring to
An electric cable extension 170 may connect the upper ESP 140 and the lower
ESP 150 such that the electric power may be further delivered to the lower ESP 150. Similar to the electric cable 103, the electric cable extension 170 may deliver control signals to the lower ESP 150 and may receive downhole data measured by the sensor 156.
The electric cable 103 and the electric cable extension 170 may be connected by a connector 160 disposed on the first ESP 140. In the example shown in
Referring now to
An auto flow sub or auto diverter valve 207 may be coupled above the lower ESP 250 (i.e., between the lower ESP 250 and the upper ESP 240) and/or above the upper ESP 240. The valve 207 may be a mechanical opening mechanism that may allow access of fluid either via the tubing 202 or from the tubing casing 299. The valve 207 may operate based on fluid pressure at the lower ESP outlet 252. The valve 207 may include a spring-loaded flapper or sliding sleeve mechanism. In such an embodiment, when an ESP 240, 250 is powered on, pressure of well fluids at the ESP outlet 242, 252 may be high enough to push open the flapper or sliding sleeve mechanism in the valve(s) 207 to allow flow up above the ESP 240, 250 to surface. However, when the ESP 240, 250 is turned off, the flapper or sliding sleeve mechanism of the valve 207 retracts, because no pressure is available to keep the valve 207 open. The valve 207 therefore closes the conduit of the ESP outlet 242, 252 and opens an access to the wellbore annulus to allow fluid to bypass the ESP and flow back down into the well.
In the example shown in
As further shown in
Still referring to
An electric cable extension 270 may connect the upper ESP 240 and the lower ESP 250 such that electric power may be further delivered to the lower ESP 250. Similar to the electric cable 203, the electric cable extension 270 may deliver control signals to the lower ESP 250 and may receive downhole data measured by the sensor 256.
In the example shown in
As can be seen in
Apart from the variations shown in
In one or more of the embodiments disclosed herein, when the upper ESP is enclosed by a pod, the connector that connects the electric cable 203 and/or electric cable extension 270 to one or more ESPs 240, 250 may be disposed on the pod of the upper ESP, instead of on the motor of the upper ESP. Further, as shown in
The casing 299, packer 205, tubing 202, and the ESPs 240 and 250 in
When the dual ESPs are configured in series, there may be scenarios where it is desired to impose a delay between the start of the upper ESP 240 and the start of the lower ESP 250. Accordingly, a delay starter 280 may be coupled to the connector 260 to impose the delay. For example, a delay starter 280 may be mounted at the location of the electric cable 203 feedthrough of the pod 206 (
Referring now to
According to one or more embodiments, voltage may be supplied to both of the ESP motors by the electric power and the power cable extension. Due to the voltage drop along the power extension cable, the voltage reaching the lower ESP motor may be less than that received by the upper ESP motor. To ensure that the voltage at the lower ESP motor is greater than the minimum voltage required to start the motor, a general rule is that the voltage reaching the motor should be at least 50% of the motor nameplate voltage for the motor to start. In practice, proper conductor sizing and soft starters or variable speed frequency controllers may be used to provide low currents during the start of the lower ESP and to reduce the voltage drop along the cable.
While not shown in the figures, the electric cable that runs from the power source may have the same structure and materials as the electric cable extension.
In
In
By using the connector and the electric cable extension, electric power and control signals may be delivered to the lower ESP via the electric cable and the electric cable extension. Likewise, downhole data measured by, e.g., the sensor may be transmitted uphole via the electric cable extension and the electric cable.
Factors to consider in selecting the design and/or configuration of the structure of the connector may include the following: toughness and rigidity of the connector to prevent the connection between the electric cable and the cable extension from breaking down, because the connector is close to a connection point of the electric and the electric cable extension; minimum bending of the electric cable at the connection point to reduce stresses; erosion and abrasion resistant surface to ensure structural integrity; resistance to chemical, mechanical attacks from wellbore liquids and gases such as H2S and CO2; sealing capabilities around the electric cable and the cable extension to prevent ingress of wellbore fluids into the motor; and overall protection of the electrical and mechanical integrity of the cable connections.
The power switch 589 may be connected to the electric cable 581 and/or the electric cable extension 582. The power switch 589 may be a mechanical switch. For example, the power switch 589 may include copper that contacts with an electromechanical actuator. The power switch 589 may also be an electronic switch. For example, the power switch 589 may be a solid state power electronics such as a silicon controlled rectifier. The power switch 589 may also be a metal-oxide-semiconductor field-effect transistor (MOSFET) or any other suitable electronic component. An electronic power switch 589 may provide soft start to the motor to reduce the voltage drop in the system.
The delay starter 580 may be controlled from the surface to impose the delay. In this case, there may be a signal from the surface that expressly instructs the delay starter to switch the lower motor on after the upper motor has started. Alternatively, the delay starter 580 may operate in an automatic mode based on the sensed downhole data and a pre-programmed amount of delay. In this mode, once the delay starter determines it is time to start, e.g., the lower ESP, the control circuit 588 sends a signal to the power switch to allow electric current to flow to the lower ESP.
As discussed above, the present disclosure provides a pumping system with dual ESPs operating simultaneously without two separate power cables to drive both the upper ESP and the lower ESP. In other words, a pumping system in accordance with embodiments disclosed herein drives dual ESPs simultaneously with a single power cable extending from the surface. The cost and complexity of a pumping system in accordance with embodiments disclosed herein may, therefore, advantageously be reduced. Further, with the reduction of the number of cables running from the power source to downhole, the number of splices above or below the packer may be reduced. This may advantageously result in a lesser susceptibility of ESP failure due to electrical failure at the splice caused by concentrated corrosive gas that accumulates just under the packer
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 the disclosure. Accordingly, the scope of the disclosure should be limited only by the attached claims.
