Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
  • G01V3/18—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for well-logging
• • E—FIXED CONSTRUCTIONS
  • E21—EARTH OR ROCK DRILLING; MINING
  • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
  • E21B47/00—Survey of boreholes or wells
  • E21B47/02—Determining slope or direction
  • E21B47/022—Determining slope or direction of the borehole, e.g. using geomagnetism
  • E21B47/0236—Determining slope or direction of the borehole, e.g. using geomagnetism using a pendulum
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V7/00—Measuring gravitational fields or waves; Gravimetric prospecting or detecting
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/40—Capture or disposal of greenhouse gases of CO2

Definitions

• Carbon dioxide (CO ? .) is a byproduct of many industrial processes.
• Sequestration of CO? underground is one possibility. Mien sequestering CO? underground, it is sometimes desirable to determine if the C0 2 has migrated from its initial location. For example, it is sometimes desirable to determine whether C0 2 has migrated to underground sources of drinking water.
• a method of monitoring storage of CO? in an underground formation can include establishing underground electrodes configured to monitor an electrical property of ax feast a portion of the formation and establishing underground micro- gravity sensors configured to monitor a density of at least a portion of the formation.
• the method can also include determining a baseline electrical property of at least a portion of the formation and determining a baseline density of at least a portion of the formation.
• the method can further include injecting CO? into the formation.
• the method can further include determining an updated electrical property of at least a portion of the formation and determining an updated density of at least a portion of the formation.
• the method can further include monitoring the underground electrodes and monitoring the underground microgravity sensors.
• the method can further include detecting a change in the electrical property of at least a portion of the formation and a. change in density of at least a portion of the formation, wherein the change in the electrical property and the change in density are indicative of C0 2 migration.
• Fig. I is a schematic diagram representing electrode placement according to an embodiment.
• Fig. 2 is an example chart depicting admittance versus gas saturation according to an embodiment.
• FIG. 3 is a schematic diagram representing micro-gravity sensor placement according to an embodiment.
• Fig. 4 is an example chart depicting depth versus gravitational change according to an embodiment.
• FIG. 5 is a flowchart depicting an example method according to an embodiment.
• C0 2 can be sequestered underground by injecting it into pre-existing boreholes, boreholes drilled specifically for the purpose of CO ? , storage, or both.
• CO? can be sequestered in compressed form at the surface prior to injection.
• CO ? is typically injected into a relatively permeable layer of a geological sub-surface formation that lies beneath one or more relatively impermeable layers.
• CO may be sequestered, for example, 4000-10,000 feet (about 1200-3048 meters) underground. This process is sometimes known as "carbon sequestration" within a technological methodology known as "carbon capture and storage"
• Embodiments allow for monitoring subterranean CO ? storage. In particular, embodiments allow for monitoring whether sequestered CO ? has migrated vertically or horizontally underground subsequent to its injection into a subterranean storase location.
• a combination of electrical and micro- gravity sensors may be used to monitor whether C0 2 sequestered underground has migrated from its initial storage location.
• the combined sensor types provide a synergy that allow for monitoring both vertical and horizontal CO ? displacement. Sensor placement and interpretation of data gathered by the installed sensors are discussed in detail herein as follows.
• Fig. 1 is a schematic diagram representing exemplary electrode placement according to an embodiment. According to certain embodiments, displacement of sequestered CO? is detected by monitoring changes in electrical current flow between sub-surface electrodes.
• Fig. ! illustrates a schematic representation of two electrodes formed by borehole metallic casings 102, 104.
• boreholes 1 12, 1 14, such as those used to extract petroleum and those used to inject C0 2 may be reinforced using metallic casings. Because such casings are typically highly conductive and subterranean, they can provide efficient preexisting electrodes for detecting underground CO? migration.
• borehole casing electrodes 102 are provided.
• Conductive wires 1 10 may be connected to power source 106 and inserted into boreholes 1 12, 1 14 such that they make electrical contact with metallic casings 102, 104 at a depth interval at feast as great as the borehole separation L, That is, the distance from the surface to the electrical contact may be at least as great as the distance between boreholes 1 12, 1 14,
• Fig. 2 include the following. Sequestration target zone 108 has height h w and a fluidic conductivity denoted by ⁇ « ,. The z-axis runs vertically in Fig. 1. The formation layer 116 above sequestration target zone 108 has a conductivity denoted by & b ⁇ , and the formation layer 118 below sequestration target zone 108 has a conductivity denoted by ⁇ ' , [0016]
• Fig, 2 is an example chart depicting electrical admittance (i.e., the reciprocal of the electrical impedance) versus gas saturation according to an embodiment. The chart depicted in Fig. 2 may represent inter-electrode admittance of the system depicted schematically in Fig, 1.
• conductivity of sedimentary rocks may be represented according to, by way of non-limiting example: a ⁇ aa w S ⁇ m Equation 1
• Equation 1 the term ⁇ represents conductivity, represents rock porosity, S w ⁇ ⁇ ⁇ S G , where So represents gas saturation, parameter a and cementation factor m vary from 0.6 to 1.5 and from 1 .3 to 3, respectively, and saturation exponent n is close to 2.
• rock conductivity of rock is highly sensitive to gas saturation. For example, if gas saturation were to vary from 0.0 to 0.95, rock conductivity may vary by as much as a factor of 400.
• Equation 2 the first and last terms represent contributions of the half-spaces above and below sequestration target zone 108, respectively.
• the second term represents admittance of the sequestration target zone itself, which may be estimated according to, by way of non-limiting example:
• Equation 4 the term ⁇ , ⁇ (r,z) may be defined according to, by way of non-limiting example:
• ⁇ command( ⁇ ) is the modified Bessel function of the second kind and of the n-th order.
• Fig. 2 plots gas saturation 202 against inter-casing admittance 204 for the system described schematically in Fig. 1.
• the curves represented in Fig. 2 represent inter-casing separations L of 10 meters, 50 meters, 100 meters, 200 meters, 300 meters, 400 meters and 500 meters.
• one of ordinary skill in the art can place electrodes in borehole casings and be able to estimate the corresponding gas saturation in sequestration target zone 108 based on observed inter- casing admittance.
• a component of certain embodiments includes estimating gas saturation based on density measurements made by micro-gravity sensors. This second component is discussed presently in reference to Figs. 3 and 4,
• Fig. 3 is a schematic diagram representing micro-gravity sensor placement according to an embodiment.
• Fig. 3 depicts borehole 302 below surface 304.
• Micro-gravity sensors 306 can be spaced along borehole 302 at 10 meter intervals.
• micro-gravity sensors 306 can be spaced at 5 meter intervals within the sequestration target zone, and at 25 meter intervals above and below the sequestration target zone.
• a single micro- gravity sensor is positioned in each borehole in the sequestration target zone (e.g., 108 of Fig. 1); in other embodiments, multiple (e.g., up to several dozen) can be placed both in and out of the sequestration target zone.
• Micro-gravity sensors 306 can be placed in a network of multiple boreholes.
• the boreholes are positioned in a square grid arrangement. Boreholes may be spaced at, by way of non-limiting example, 20 meter intervals, 100 meter intervals, or at other intervals.
• micro-gravity sensor placement parameters discussed herein are representative but non-limiting; other micro-gravity sensor placements are contemplated.
• Micro-gravity sensors 306 are communicatively coupled to computing device 308.
• Computing device 308 may detect and store readings from micro-gravity sensors 306 continuously, at periodic intervals, or upon command.
• Example periodic intervals include daily, weekly, monthly, and quarterly.
• An exemplary micro-gravity sensor is the Deep Density Borehole
• micro-gravity sensors 306 may be capable of resolutions on the order of 1 ⁇ iGai.
• Fig. 4 is an example chart depicting depth 404 versus gravitational change 402 according to an embodiment.
• the chart depicted in Fig. 4 illustrates changes in gravity subsequent to C0 2 injection into the sequestration zone as compared to gravity prior to injection.
• the presence of C0 2 in a fluid alters the density of the fluid.
• the density may decrease.
• supercritical CO ? replaces hydrocarbons in a formation, the density may increase.
• FIG. 4 Two different boreholes are represented in Fig. 4: an existing borehole and a nearby borehole used as the CO? injection well.
• the CO? plume corresponding to the existing borehole lies at approximately 1990-2000 meters belo the surface as shown at portion 406 of the graph, and the CO ? plume corresponding to the injection well lies at approximately 2050-2085 meters below the surface as shown at portion 408 of the graph.
• the curves represent the difference in vertical attraction due to gravity by subtracting the gravitational response as observed before and after injection of the CO ? .
• a decrease in vertical gravity is observed at the top of the reservoir. This is because the net density in the reservoir is negative since CO ? is less dense than the water it has replaced, so the vertical gravitational force is negative.
• An increase in net gravity acceleration is observed below the reservoir. This is because the net density is negative above the sensor giving rise to a polarity change in acceleration measured.
• Fig. 5 is a flowchart depicting an example method according to an embodiment.
• an initial model is obtained.
• the model under discussion represents the subterranean structure of the sequestration target zone and surroundings. It typically depicts the various sedimentation and other layers of geological or sequestration significance and their associated electrical and density properties.
• the initial mode! may be obtained using, by way of non-limiting example, seismic surveys employing reflective seismology and the electrical and density properties can be obtained by well log or core measurements from nearby wells.
• Electrodes are established. This step is discussed in detail above in reference to Figs, 1 and 2.
• gravity sensors are established. This step is discussed above in reference to Figs. 3 and 4.
• a baseline electrical property is established. This step occurs prior to CO? injection.
• the electrodes discussed in reference to block 502 may ⁇ be used to that end.
• the electrical property may be, by way of non-limiting example, a measure of resistivity or admittance.
• a baseline density is established. Again, this step occurs prior to C0 2 injection.
• the micro-gravity sensors discussed above in reference to block 508 may be used for that purpose.
• the baseline density may reflect or be derived from micro-gravity readings.
• the initial model is revised.
• the revision may take into account the baseline electrical property and density readings obtained at blocks 506 and 508.
• the initial model is revised by performing an inversion of the model, known to those of skill in the art.
• empirical data may be used to back-calculate parameters of the model.
• the inversion may utilize the baseline density data, the baseline electrical property data, or both (e.g., a braid or "joint" inversion).
• other types of sensors for example seismic sensors, can be utilized in the readings obtained. For example, readings including one or more of seismic electrical and seismic density. Then, electrical density and seismic electrical and density joint inversions can be performed,
• CO ? is injected. This process may proceed over a time period that may span days or months.
• An exemplary, non-limiting injection rate is two kilograms per second. Other injection rates are also contemplated.
• an updated electrical property is obtained.
• the updated electrical property may be obtained as discussed above in reference to block 506.
• an updated density is determined.
• the updated density may be obtained as discussed above in reference to block 508.
• the model is revised.
• the model may be revised based on the updated electrical property obtained at block 514 and the updated density obtained at block 516.
• the updated model may be generated by way of inversion based on one or both of the updated electrical and density determinations.
• the revised model is intended to reflect the presence of sequestered CO ?
• the revised model may be compared to the model obtained at block 510 in order to determine the geological differences caused by the new presence of sequestered CO?. For example, the graph of Fig. 4 reflects such differences with respect to gravity.
• electrode readings are monitored, and at block 522 readings from the micro -gravity sensors are monitored.
• the monitoring may occur continuously, periodically, or on command. If periodically, the monitoring may occur daily, weekly, monthly, quarterly, or yearly.
• the data detected by the respective sensors may be stored electronically in persistent memory of a computer.
• CO? migration is detected. This may be performed by comparing the revised model obtained at block 51 8 to ars inversion model based on the data obtained at blocks 520 and 522. Alternately, or in addition, the migration may be detected by detecting changes in the parameters themselves. Using both electrical properties and micro-gravity readings, the lateral and vertical extent of such migration may be ascertained.

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• 2012
  • 2012-10-03 CN CN201280076277.1A patent/CN104704394A/zh active Pending
  • 2012-10-03 WO PCT/US2012/058530 patent/WO2014055071A1/fr not_active Ceased
  • 2012-10-03 CA CA2883932A patent/CA2883932A1/fr active Pending

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