BACKGROUND
Injection wells are used for various purposes in the drilling industry. As one example, injection fluid (e.g., water, CO2) may be injected through the injection well toward a producing well (producing oil, for example) to increase pressure and thereby encourage production. However, once the injection fluid front reaches the production well such that the injection fluid is being produced, the production well is no longer viable. Prior systems to monitor injection fluid have been disposed in the production well or one or more monitor wells (separate from the production well and injection well) or some combination thereof. The systems obtain resistivity or conductivity (inversely proportional to resistivity) measurements around the borehole in which they are located and can determine the boundary between materials that have discernibly different resistivity values (e.g., the boundary between a production fluid like oil and an injection fluid like water). When such a system is located in the production well or in a monitor well in the vicinity of the production well, it indicates when the fluid front from the injection well has reached or nearly reached the production well. However, the information is not timely enough to control the injection process to potentially prolong the use of the production well. Prior methods of monitoring are also problematic because the injected fluid may not necessarily reach the production well due to heterogeneity and/or permeability anisotropy around the injection well. In this case, the direction and flow rate from the injection well is unknown. Another exemplary purpose of an injection well is for the introduction of material into an underground storage reservoir. In this case, the seal on the storage reservoir must be monitored to ensure that the stored material is not leaking into the surrounding area.
SUMMARY
According to an aspect of the invention, a method of monitoring an injection substance injected into an injection well penetrating the earth includes disposing a monitoring system in a borehole, both a transmitting and a receiving portion of the monitoring system being disposed in the borehole; injecting the injection substance into the injection well; and monitoring, using a processor processing the received signal, flow of the injection substance out of the injection well.
According to another aspect of the invention, a method of monitoring an underground reservoir storing a substance introduced through an injection well includes disposing a monitoring system in a borehole, both a transmitting portion and a receiving portion of the monitoring system being disposed in the borehole; injecting the injection substance into the injection well for storage in the underground reservoir; and monitoring, using a processor processing the received signal, boundary conditions surrounding the underground reservoir.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the drawings wherein like elements are numbered alike in the several Figures:
FIG. 1 illustrates a cross-sectional view of an injection substance monitoring system according to an embodiment of the invention;
FIG. 2 illustrates a cross-sectional view of an injection substance monitoring system according to another embodiment of the invention
FIG. 3 depicts the monitoring system in the injection well according to an embodiment of the invention;
FIG. 4 depicts the monitoring system in the injection well and a monitor well according to an embodiment of the invention;
FIG. 5 depicts the monitoring system in the injection well and a monitor well according to another embodiment of the invention
FIG. 6 depicts the monitoring system according to an embodiment of the invention
FIG. 7 illustrates a cross-sectional view of a monitoring system according to an embodiment of the invention;
FIG. 8 illustrates a cross-sectional view of an injection substance monitoring system according to an embodiment of the invention; and
FIG. 9 is a flow diagram of a method of monitoring an injection fluid according to an embodiment of the invention.
DETAILED DESCRIPTION
As noted above, prior injection monitoring systems have been positioned in the production well or in monitor wells near the production well. An exemplary injection arrangement positions a number of injection wells surrounding the production well. The injections wells may even be essentially equidistant from the production well, and each injector may even inject the injection fluid at the same rate. However, inhomogeneity in the reservoir may render the injection system inhomogeneous (injection fluid from each injection well reaches the production well at a different time or not at all). For example, the injection fluid front from a given injection well may be advancing toward the production well faster than the injection fluid front from any of the other wells. If this were determined early in the injection process, the given injection well may be choked off to increase the time until an injection fluid front reaches (and contaminates) the production well. However, a monitoring system in the production well would not be capable of making such a determination in time to prolong the production. This is because the system in the production well would only identify the injection fluid front when it has already approached the production well. Also, if one of the other injection wells' injection fluid had been misdirected away from the production well due to the permeability anisotropy around that injection well, the production well would not detect that fluid front over a length of time but would not provide any information about the directivity of that injection fluid.
Embodiments detailed herein describe a method of monitoring boundary conditions from the injection well itself. By detecting the boundary between the material injected through the injection well and surrounding material, the fluid front advancing toward a production well (or in an unintended direction other than the direction of the production well) or material injected into a storage reservoir may be effectively monitored during its travel into the reservoir and throughout the useful life of the reservoir.
FIG. 1 illustrates a cross-sectional view of an injection substance 101 monitoring system 130 according to an embodiment of the invention. While any system that resides within a single injection well and monitors boundary conditions from that injection well may be used, a transient electromagnetic (EM) system including a transmitter 110 and one or more receivers 120 pair in the injection well 100 is discussed as an exemplary monitoring system 130 in the embodiment discussed with reference to FIG. 1 and is detailed with reference to FIG. 2. The production well 150 is shown as another borehole penetrating the earth 160 in an area including a formation 165, which represents any subsurface material of interest in the production. A computer processing system 140 may process the data obtained by the monitoring system 130. The processing may include taking resistivity measurements and finding the fluid boundary, if any, based on the received conductivity. In alternate embodiments, downhole electronics 145 that are part of a downhole tool 105 may execute the processing. FIG. 2 illustrates a cross-sectional view of an injection substance 101 monitoring system 130 according to another embodiment of the invention. FIG. 2 shows a horizontal production well 150 and a horizontal injection well 100. All of the embodiments of the monitoring system 130 discussed herein apply to both vertical wells (see e.g., FIG. 1) and horizontal wells.
FIG. 3 depicts the monitoring system 130 in the injection well 100 according to an embodiment of the invention. As noted above, the exemplary transient EM monitoring system 130 is one embodiment of a system that may be used, but any system that facilitates the monitoring of fluid boundary dynamics from the injection well 100 may be used to implement embodiments of the method and system described herein. For example, a continuous-wave system rather than a transient EM system may be used as the monitoring system 130. The transmitter 110 may be a three component transmitter with antennas oriented in the z, x, and y directions. These directions are parallel to the longitudinal axis of the injection well 100, orthogonal to the longitudinal axis and oriented toward the production well 150, and orthogonal to the longitudinal axis and transverse to the production well 150, respectively. An array of receivers 120a-120n may be disposed in the injection well 100. Each of the receivers 120 may be a three component receiver with antennas oriented in the x, y, and z directions. The transmitter 110 and one or more receivers 120 may be moved along the length of the injection well 100 and may provide information as a function of depth. In other embodiments, the transmitter 110 and one or more receivers 120 may be affixed to a particular position within the injection well 100. In still other embodiments, a number of sets of transmitters 110 and receivers 120 may be positioned and may even be affixed along the length of the injection well 100. FIG. 4 depicts the monitoring system 130 in the injection well 100 and a monitor well 410 according to an embodiment of the invention. According to the alternate embodiment shown in FIG. 4, some of the array of receivers 120b-120n, are disposed in a monitor well 410 while the transmitter 110 and one receiver 120a (or more) are disposed in the injection well 100. FIG. 5 depicts the monitoring system 130 in the injection well 100 and a monitor well 510 according to another embodiment of the invention. According to the alternate embodiment shown in FIG. 5, one or more receivers 120 may be in a monitor well 510 while the transmitter 110 is disposed in the injection well 100. In a transient EM monitoring system 130, this separation of the transmitter 110 and one or more receivers 120 is possible when synchronization of the transmitter 110 and receiver(s) 120 is included. The synchronization (to within a few microseconds) may be achieved, for example, via hardwire or fiber optic connection between the transmitter 110 and receiver(s) 120. In alternate embodiment, wireless synchronization of the transmitter 110 and receiver(s) 120 may be performed.
While each of the various types of transmitter/receiver systems that may be used as the monitoring system 130 may have individual strengths, the exemplary transient EM monitoring system 130 addresses two concerns. First, transient (time-domain) measurements relative to continuous-wave measurements provide improved spatial resolution. Second, signal-to-noise ratio is improved by increasing the strength of the transmitter and receiver magnetic dipoles. The transmitter 110 and receiver 120 of the present embodiment are designed to generate a relatively large switchable dipole (e.g., dipole moment of 1 kAm2) with power consumption that is more than a hundred times less than with a conventional long-coil. The monitoring system 130 measures conductivity. The monitoring system 130 operates by altering the transmitted electromagnetic (EM) field to produce a transient EM signal. The receiver 120 receives a signal based on the transient EM signal transmitted by the transmitter 110. This received signal represents the conductivity of the surrounding material.
By detecting a transition in conductivity of that surrounding material, the fluid front of the injection substance 101 may be detected and its directivity and speed may be monitored. The directivity of the injection substance 101 is based on the permeability anisotropy around the injection well 100. That is, the injection substance 101 will not flow in all directions uniformly from the injection well 100 and, as noted above, may not reach a targeted production well 150 at all within a given period of time. By monitoring the flow of the injection substance 101, the permeability anisotropy around the injection well 100 may be determined. Because the exemplary monitoring system 130 (transient EM) measures conductivity, an injection substance 101 that has a lower conductivity than that of surrounding material (e.g., oil around a production well 150) may be monitored for a longer distance away from the injection well 100 than an injection substance 101 with a higher conductivity than that of surrounding material. For example, CO2 has a lower conductivity than oil. Thus, when CO2 is the injection substance 101 injected into the injection well 100, it may be monitored as it advances toward the oil for a greater distance than if water (with a higher conductivity than oil) were used as the injection substance 101.
FIG. 6 depicts the monitoring system 130 according to an embodiment of the invention. The transient EM monitoring system 130 is again used as an example. In the embodiment shown in FIG. 6, the borehole 330 (e.g., injection well 100 or monitor borehole 410, FIG. 4810, FIG. 8) includes a casing 310. In this case, especially if the casing is conductive (e.g., steel), the magnetic flux going through the casing 610 may result in the production of eddy currents. Thus, in the embodiment shown in FIG. 6, a magnetically permeable or ferrite material 620 surrounds the casing 610. The lower impedance path created by the magnetically permeable or ferrite material 620 reduces the magnetic flux through the casing 610. In this case, the transient EM monitoring system 130 is mounted outside the casing 610 and outside the magnetically permeable or ferrite material 620.
FIG. 7 illustrates a cross-sectional view of a monitoring system 130 according to an embodiment of the invention. In the embodiment shown in FIG. 7, an injection substance 101 is injected into the injection well 100 for storage in an underground reservoir 710. The injection substance 101 may be carbon dioxide, waste water, or natural gas, for example. By using the monitoring system 130, the fluid front of the injection substance 101 into the reservoir 710 as well as any leak from the reservoir 710 may be monitored.
FIG. 8 illustrates a cross-sectional view of an injection substance 101 monitoring system 130 according to an embodiment of the invention. The monitoring system 130 according to the present embodiment resides in a monitor borehole 810 in proximity to the injection well 100. For example, if the distance D from the injection well 100 to the production well 150 is 100 feet, the distance d from the injection well 100 to the monitor borehole 810 may be approximately 5 to approximately 10 feet. Because the monitor borehole 810 includes the monitoring system 130 to monitor the injection substance 101 from the injection well 100 (rather than a fluid front approaching the production well 150) and because the monitor borehole 810 is proximate to the injection well 100, a single monitor borehole 810 is sufficient though two or more monitor boreholes 810 may be used. All of the features discussed with reference to the monitoring system 130 in the injection well 100 above apply, as well, to the monitoring system 130 in the monitor borehole 810. For example, the monitor borehole 810 may include a casing 610 and a permeable or ferrite material 620 (FIG. 6). The monitoring system 130 in the monitor borehole 810 may be a continuous-wave system rather than a transient EM system. The monitor borehole 810 may be used to monitor injection substance 101 intended to encourage production in the production well 150 and to monitor injection substance 101 stored in an underground reservoir 710 (FIG. 7).
FIG. 9 is a flow diagram of a method 900 of monitoring an injection substance according to an embodiment of the invention. The method 900 according to the exemplary embodiment described herein uses the transient EM monitoring system 130 described with reference to FIG. 2. The method 900 includes inserting a monitoring system 130 transmitter 110 and one or more receivers 120 into the injection well 100 (block 910). At block 920, the method 900 includes injecting the injection substance 101 into the injection well 100. At block 930, the method 900 includes altering the transmitted EM field to produce a transient EM signal out of the injection well 100. At block 940, receiving a received signal based on the transient EM signal facilitates determining conductivity. Monitoring the injection substance 101 based on the received signal (block 950) includes monitoring the fluid front based on a difference in conductivity between the injection substance 101 and the surrounding material. This monitoring may include the use of time-lapse measurements to determine the motion of the injection fluid front. This monitoring may include monitoring injection fluid directed to a production well 150 to increase production. The monitoring may also include monitoring a substance injected into an underground reservoir 710 (FIG. 7).
While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.
Patent Application
20140182842
