Patent Grant
8006757
Oil well production can involve pumping a well fluid that is part oil and part water, i.e., an oil/water mixture. As an oil well becomes depleted of oil, a greater percentage of water is present and subsequently produced to the surface. The “produced” water often accounts for at least 80 to 90 percent of a total produced well fluid volume, thereby creating significant operational issues. For example, the produced water may require treatment and/or re-injection into a subterranean reservoir in order to dispose of the water and to help maintain reservoir pressure. Also, treating and disposing produced water can become quite costly.
One way to address those issues is through employment of a downhole device to separate oil and water and to re-inject the separated water, thereby minimizing production of unwanted water to surface. Reducing water produced to surface can allow reduction of required pump power, reduction of hydraulic losses, and simplification of surface equipment. Further, many of the costs associated with water treatment are reduced or eliminated.
However, successfully separating oil/water downhole and re-injecting the water is a relatively involved and sensitive process with many variables and factors that affect the efficiency and feasibility of such an operation. For example, the oil/water ratio can vary from well to well and can change significantly over the life of the well. Further, over time the required injection pressure for the separated water can tend to increase.
In general, the present application provides a system and method for processing well fluid downhole. The system and methodology utilize equipment to separate a well fluid downhole into a water component and an oil component. The water component is injected into a downhole injection zone and the oil component is produced to a desired collection location. The separation of water and oil can be controlled by selecting an appropriately sized flow restrictor for use in limiting the flow of one or both of the water and the oil. Additionally, a sensor system is used to monitor a well characteristic that enables adjustment of the downhole fluid processing based on well characteristic data from the sensor system.
Certain embodiments will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and:
In the following description, numerous details are set forth to provide an understanding of the present application. However, it will be understood by those of ordinary skill in the art that embodiments may be practiced without many of these details and that numerous variations or modifications from the described embodiments may be possible.
An embodiment generally relates to downhole oil/water separation, and more particularly to managing back-pressure to manipulate the oil/water separation. One way to control separation of fluids is by regulating back-pressure applied to the oil stream and/or the water stream. One way to regulate back-pressure is by regulating a flow-restriction (i.e., throttling) of the oil stream and/or the water stream exiting the oil/water separator. Embodiments herein relate to equipment that allows a stream to be throttled, i.e., a back-pressure to be manipulated. The magnitude of throttling can cover a range from completely closed to wide open depending on the oil/water content of the well fluid.
The form and function controlling backpressure and related flow is dependent upon the injection zone orientation relative to the producing zone (injection zone uphole or downhole of the producing zone). Some differences between the two orientations relate to injecting uphole where the device can throttle and vent to a tubing annulus in a single operation, and injecting downhole where the device may need to throttle the flow “in-line”, i.e. receive the injection flow from the tubing, throttle the flow, and then return the flow to another tube headed toward the injection zone. Some or all of these factors can be considered. The diameter of a throttle opening can generally be from 0.125 to 1.0 inches although other diameters may be used in some applications.
In addition, a sensor system can be used to provide feedback and to facilitate the downhole fluid processing, by, for example, improving the control over backpressure which, in turn, optimizes oil and water separation. The sensor system is useful in monitoring a variety of characteristics related to the downhole fluid processing, including pressure, temperature, chemistry, vibration, fluid composition, and other characteristics. Examples of sensors that can be incorporated into the sensor system include oil-in-water sensors, sand-in-water sensors, flow meters, pressure sensors, chemistry sensors, and vibration sensors that enable the system operation to be optimized. In some applications, the sensor system also enables real-time corrections based on data provided by the sensor system to reduce the risk of system failure or damage.
In many applications, the well fluid is separated into oil and water. However the oil component may contain some or much water and, similarly, the water component may contain some oil. Oil-in-water sensing enables an operator to make adjustments to the system to balance the separation process to optimize separation efficiency. For example, a flow-restrictor can be sized to provide the desired backpressure to better optimize separation efficiency. Oil-in-water sensors measure the oil content in the injected water stream and may send the data to a surface location via a suitable communication line, such as a power cable.
For a variety of reasons, including local regulations, it may be desirable to limit oil-in-water levels for certain applications. The sensor system enables monitoring to ensure the separated water does not exceed the desired/required level of oil in the water component. The sensor system can be designed to provide an alarm or other indication to an operator to enable adjustment to the downhole fluid processing parameters. For example, adjustments can be made to the backpressure via the flow-restrictor, or adjustments can be made to other components to regulate well head pressure, to adjust speed of an electric submersible pump, or to make other adjustments. Furthermore, monitoring of the oil-in-water content of the water stream injected into an injection zone can be useful in limiting potentially harmful impacts on the injection zone. The sensor system provides operators with advance notice to enable the taking of corrective action, such as scheduling a stimulation procedure before the injection zone becomes severely plugged.
The sensor system also may comprise other sensors that facilitate optimal downhole fluid processing, such as particulate sensors. For example, in applications that produce from sandstone formations, sand can be produced and separated with the water component in the injection stream. For example, the startup procedure utilized in operating electric submersible pumping systems can impact the amount of sand produced. The ability to determine production of sand and the quantity of sand produced enables an operator to adjust the flow of the pumping system. By positioning a sand-in-water sensor in the water injection stream, the sensor can provide data to an operator that enables adjustment to the downhole fluid processing. Producing sand in the injection stream can also plug the injection zone.
In many applications, the volume of fluid injected into the injection zone is monitored and recorded. The sensor system may comprise a variety of sensors that monitor the injection flow rate along with injection pressure and temperature to enable, for example, a real-time or near real-time assessment of injection zone performance. Decreases in flow rate, for example, can be indicative of injection zone plugging or other problems that require remediation. Plugging can result from the injection of solids, scale precipitation in the wellbore or the formation, clay migration, swelling within the injection interval, accumulation of oil in the pore throats near the wellbore, or from other factors. The monitoring and recording of data from the various sensors also enables certain pressure transient analyses that can determine zonal properties, such as permeability, skin damage and reservoir extent.
The sensor system also may utilize chemical sensors for monitoring chemical properties downhole to facilitate a determination as to whether conditions exist for the precipitation of scales or corrosion. For example, measuring pH and/or the presence of certain ions using electrochemical techniques facilitates the development and optimization of scale mitigation strategies, e.g. introduction of scale inhibitor chemicals downhole via a chemical injection line. By way of example, a sensor can be located to measure the injection stream pH and to give an overall indication of the fluid condition. Chemical sensors also can be used to measure or sense the presence of corrosive chemical components, such as H2S and CO2. In these applications, the sensor system incorporates chemical sensors to facilitate the development and optimization of corrosion inhibitor strategies.
Alternately, the flow-restrictor 304 can have a variable size throttle orifice so that replacement of the flow-restrictor is not required to vary orifice size. The orifice size can be varied mechanically in many ways, e.g., at surface by hand, by a wireline tool, a slickline tool, a coil tubing tool, a hydraulic line from the surface, by an electric motor controlled by electrical signals from the surface or from wireless signals from the surface, or by an electrical motor receiving signals from a controller downhole. Check valves 302 can be located in the oil conduit 204 and/or the water conduit 206. The check valves 302 can prevent fluid from moving from the oil conduit 204 and the water conduit 206 down into the oil/water separator 200, thereby causing damage to the device. Packers can be used to isolate parts of the apparatus within the wellbore. For example,
The above noted configurations also can be used to inject stimulation treatments downhole.
The flow-restrictor 304 may have an attachment part 702 that is used to connect to a downhole tool (not shown) to place and remove the flow-restrictor 304 from the flow-restrictor pocket 610. As noted earlier, the downhole tool can be connected to any relay apparatus, e.g., wireline, slickline, or coiled tubing.
There are many ways to determine an oil/water content of a well fluid. Well fluid can be delivered to surface where a determination can be made. Alternately, a sensor can be located downhole to determine the oil/water ratio in the well fluid. That determination can be transmitted uphole in many ways, e.g., electrical signals over a wire, fiber-optic signals, radio signals, acoustic signals, etc. Alternately, the signals can be sent to a processor downhole, the processor instructing a motor to set a certain orifice size for the flow-restrictor 304 based on those signals. The sensor can be located downstream from the well fluid intake of the oil/water separator, inside the oil/water separator, inside the redirector, inside the flow-restrictor, upstream of the oil/water separator, outside the downhole device and downhole of the well fluid intake, outside the downhole device and uphole of the sell fluid intake, or outside the downhole device and at the level of the well fluid intake.
One embodiment shown in
Referring generally to
In operation, well fluid is drawn in through production zone 826 via electric submersible pumping system 100 which may comprise a variety of pumping system components. The well fluid is directed through separator 200 where it is separated into a water component and an oil component. It should be noted that the water component may comprise small amounts of oil and the oil component may comprise small or large amounts of water, and those amounts may be monitored to facilitate optimization of the fluid processing.
The separated fluids are directed into redirector 250 which directs the oil stream up through a tubing 828 while redirecting the water stream back down into the wellbore through tubing 830. In this embodiment, the sensor system 822 is located below the electric submersible pumping system 100. The water stream is directed down past sensor system 822, through a packer 832, and out through a discharge tubing 834 into injection zone 824. The packer 832 isolates the injection zone 824 from the production zone 826 along the wellbore. The sensor system 822 can measure a variety of characteristics related to the water component, but the sensor system 822 also may comprise sensors that detect and/or monitor various other characteristics related to the produced oil stream, the surrounding formation, the operation of well system components, or to other aspects of the fluid processing.
In an alternate embodiment, well system 820 is arranged so the water component is injected into an injection zone 824 located above the production zone 826, as illustrated in
In operation, well fluid is again drawn in through production zone 826 via electric submersible pumping system 100. The well fluid is drawn in through an intake tubing 836 that extends through a packer 838 separating the production zone 826 from the upper injection zone 824. The intake tubing 836 is connected to a shroud 840, and the well fluid from production zone 826 is drawn into the shroud 840. Electric submersible pumping system 100 is located within shroud 840 to intake the well fluid and to direct the well fluid through separator 200 where it is separated into the water component and the oil component.
The separated fluids are then moved past sensor system 822 and into redirector 250 which directs the oil stream up through tubing 828 while discharging the water component into an annulus 842 via appropriate discharge ports 844. Upward movement of the water component is blocked by a packer 845 so that the water is forced downwardly along an exterior of shroud 840. The water component travels downwardly until being directed into injection zone 824.
As illustrated schematically in
Depending on the configuration of the overall well system, a variety of additional or alternate sensors 846 also can be utilized with sensor system 822. For example, an oil-in-water sensor 854 may be used to monitor the oil content in the injected water stream. Additionally, a particulate sensor 856, such as a sand-in-water sensor, can be used to monitor the amount of sand entrained in the water component to enable operational adjustments of well system 820. Other examples of sensors that may be utilized in sensor system 822 include a temperature sensor 858 and a chemical/composition sensor 860. Sensors 858 and 860 are located, for example, along one or both of the water stream and the oil stream to track fluid characteristics for optimization of the fluid downhole processing, as discussed above.
The various sensors detect and/or monitor the desired characteristics and output data to a suitable data relay 862 used to transfer data to, for example, a surface location for analysis and operational adjustment. The data obtained by sensors 846 can be transmitted to the surface in real-time for real-time analysis to enable rapid adjustment of well system operation. In one embodiment, the data relay 862 comprises an electric submersible pumping gauge positioned at a suitable location, such as a base of the submersible motor 110. The electric submersible pumping gauge may be used to communicate data to and/or from the surface through the power cable used to power motor 110. Alternatively, data relay 862 may comprise a cable-to-surface system which transmits data to and/or from a surface location via a separate cable run downhole. However, some or all of the sensors can have dedicated communication lines.
Referring generally to
The sensor package 864 also comprises pressure sensor 848 which can be exposed to pressure in the tubing via a pressure port 870. In this particular example, a differential pressure sensor is used instead of two absolute pressure sensors. It should be noted that a variety of the other sensors 846, discussed above, may be incorporated into the sensor package 864 or can be positioned at other locations along well system 820 to detect and/or monitor desired characteristics related to the downhole fluid processing.
A similar sensor package 864 is illustrated in
Additionally, sensor package 864 and other sensors can be packaged and arranged in a variety of configurations. For example, additional sensors 846 may be mounted in a housing 874 of the sensor package 864/flow meter 866. The housing 874 is made larger, as necessary, to incorporate multiple sampling ports for the various sensors. The various sensors within housing 874 may be connected to data relay 862 to enable transfer of data to the surface via a single connection. In other embodiments, individual sensors or groups of sensors may be mounted in separate electronics housings with, for example, separate communication lines.
In another example, one or more of the sensors 846 is positioned as an integral part of a flow control manifold, e.g. redirector 250 or an injection valve. In this example, the sensor sampling locations may be housed inside the flow control manifold rather than in a separate, stand-alone housing. When water is injected in a lower injection zone, the flow control manifold can be either an upper or a lower manifold. In other applications, the sensors can be installed inside a sensor carrier located in a concentric seal bore with a retrievable injection valve. In this example, the sensor carrier may be retrieved periodically to place new sensors in the completion. Telemetry with the sensor carrier may be accomplished via “short hop” telemetry or through some other contact based telemetry pickup. By way of further example, the sensors may be located inside an injection valve without the addition of a separate sensor carrier.
In addition to remote measurement of flow characteristics with sensors 846, the well system 820 also may utilize systems for taking samples of fluid, such as samples of the injected fluid. As illustrated in
For some embodiments, the sampling chamber 878 may be activated by a wireline or another suitable conveyance that extends to the surface. In one example, a tool 884 is designed to engage the sampling chamber structure 878 to enable placement and retrieval of the sampling chamber structure via a wireline 886 or another suitable mechanism. By way of example, the sampling chamber 878 may comprise a sampling tube that is pulled to the surface from the flow control manifold 880 to allow periodic fluid sampling.
In other embodiments, the sampling chamber 878 is formed as part of the flow control valve 882 which can be retrieved to bring small amounts of injection fluid to the surface via, for example, wireline techniques. In some applications, the sampling chamber 878 may be run downstream in a concentric seal bore to an injection valve. After being installed and after allowing the well system to operate under normal conditions for a period of time, e.g. one to two days, the sample chamber can be retrieved via wireline or other suitable technique.
The sampling chamber 878 also may comprise a variety of internal elements 888 to facilitate sampling and evaluation of the sample fluid. For example, the internal elements may comprise filter material to filter out solids or special electrolytic metals to collect specific ions or to check the pH value of the injection fluid stream. The internal elements 888 also may comprise a filter material to collect oil droplets for facilitating analysis of the oil-in-water concentration. By way of further example, the sample chamber can comprise sensors to provide a live, real-time connection to the surface for fluid sample analysis at the surface.
Referring generally to
The embodiments described above provide examples of well systems that can be used to facilitate downhole fluid processing. The various sensor systems enable a wide variety of data to be obtained on the separation and injection of fluids downhole even when the injection fluid is not pumped to the surface. Furthermore, the sensor system can be designed to enable real-time analysis of downhole characteristics for some or all of the characteristics monitored. Regardless, the data obtained via the sensor system 822 enables improved adjustment to the operation of well system 820 to better optimize the fluid processing. For example, the data can be used to adjust back pressure via flow-restrictor 304 or to perform other actions that limit risk and/or improve the efficiency of operation. Furthermore, a wide variety of components can be utilized in sensor system 822 and in the overall well system 820.
Accordingly, although only a few embodiments have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this application. Such modifications are intended to be included within the scope as defined in the claims.
The following is a continuation-in-part of a prior patent application Ser. No. 11/953,970, filed Dec. 11, 2007, now U.S. Pat. No. 7,814,976, which is based on and claims priority to Provisional Application No. 60/969,066 that was filed on Aug. 30, 2007.
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