Abstract:
A method of monitoring an injection substance injected into an injection well penetrating the earth and a method of monitoring an underground reservoir storing a substance introduced through an injection well are described. The methods include disposing a monitoring system in a borehole, both a transmitting and a first receiving portion of the monitoring system being disposed in the borehole. The method of monitoring an injection substance also includes 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. The method of monitoring an underground reservoir includes 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.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a Non-Provisional Application of U.S. Provisional Application No. 61/746,180 filed Dec. 27, 2012, the disclosure of which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    Injection wells are used for various purposes in the drilling industry. As one example, injection fluid (e.g., water, CO 2 ) 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 
       [0003]    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. 
         [0004]    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 
         [0005]    Referring now to the drawings wherein like elements are numbered alike in the several Figures: 
           [0006]      FIG. 1  illustrates a cross-sectional view of an injection substance monitoring system according to an embodiment of the invention; 
           [0007]      FIG. 2  illustrates a cross-sectional view of an injection substance monitoring system according to another embodiment of the invention 
           [0008]      FIG. 3  depicts the monitoring system in the injection well according to an embodiment of the invention; 
           [0009]      FIG. 4  depicts the monitoring system in the injection well and a monitor well according to an embodiment of the invention; 
           [0010]      FIG. 5  depicts the monitoring system in the injection well and a monitor well according to another embodiment of the invention 
           [0011]      FIG. 6  depicts the monitoring system according to an embodiment of the invention 
           [0012]      FIG. 7  illustrates a cross-sectional view of a monitoring system according to an embodiment of the invention; 
           [0013]      FIG. 8  illustrates a cross-sectional view of an injection substance monitoring system according to an embodiment of the invention; and 
           [0014]      FIG. 9  is a flow diagram of a method of monitoring an injection fluid according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    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&#39; 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. 
         [0016]    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. 
         [0017]      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. 
         [0018]      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  120   a - 120   n  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  120   b - 120   n,  are disposed in a monitor well  410  while the transmitter  110  and one receiver  120   a  (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. 
         [0019]    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 kAm 2 ) 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. 
         [0020]    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, CO 2  has a lower conductivity than oil. Thus, when CO 2  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 . 
         [0021]      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. 4   810 ,  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 . 
         [0022]      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. 
         [0023]      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 ). 
         [0024]      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 ). 
         [0025]    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.