Multi-Transient ElectroMagnetics


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  • Multi Transient ElectroMagnetics. Table of content: (sorry Add 3 to numbers above 9!) 2-5 What MTEM is. Logging Before Drilling 6-9 MTEM applications 10-11 EM techniques 12-21 MTEM method 22-26 – France test and Reciprocity 27-40 RTA 41-46 Processing and Inversion 47-49 Data Examples 49-50 Recording System 51 Conclusion
  • Multi-Transient ElectroMagnetics

    1. 1. Multi-Transient ElectroMagnetics Multi-Transient EM Aug 2007
    2. 2. The need for an EM solution <ul><li>Seismic methods determine structure </li></ul><ul><li>The structure may reveal a potential reservoir (in general a porous rock bounded by a cap) </li></ul><ul><li>The porous rock contains a fluid (water or hydrocarbons, or a mixture) but seismics cannot usually determine the nature of that fluid – drill! </li></ul><ul><li>Resistivity – a physical rock property determined through EM – can make that distinction – drill in the right place! </li></ul>
    3. 3. Resistivities of Rocks Diagram courtesy Henri Brasse
    4. 4. Fluid saturation and rock properties P-wave velocity is affected only slightly by hydrocarbon saturation in a porous rock. Resistivity can vary by more than an order of magnitude. Picture redrawn from Wilt M. and Alumbaugh D. 1998, The Leading Edge 17, 487-492.
    5. 5. Direct Resistivity Indicator Seismic traces Seismic amplitudes and attributes Logging measurements Logging before drilling MTEM Resistivity
    6. 6. MTEM for resistivity <ul><li>MTEM is sensitive to transverse resistance. </li></ul><ul><li>Red is more resistive. </li></ul><ul><li>Stronger resistivity comes from: </li></ul><ul><ul><li>Thicker interval </li></ul></ul><ul><ul><li>Higher saturation </li></ul></ul><ul><ul><li>Higher porosity </li></ul></ul><ul><ul><li>Less clay and shale </li></ul></ul>
    7. 7. <ul><li>Cases </li></ul><ul><li>Gas storage monitoring </li></ul><ul><li>Imaging Heavy Oil </li></ul><ul><li>Imaging in structurally complex subsurface </li></ul><ul><li>Imaging thrust belt. </li></ul><ul><li>Imaging where seismic and drilling is very expensive </li></ul><ul><li>Locating steam flood front in SAGD production monitoring </li></ul><ul><li>Identifying channel sands with low acoustic impedance contrast </li></ul><ul><li>Proving up reserves to increase reserves-production ratio </li></ul><ul><li>De-risking drilling location decisions. </li></ul>MTEM Challenges to date
    8. 8. Gas storage monitoring
    9. 9. Shallow Heavy Oil resistivity scale
    10. 10. Thrust Belt
    11. 11. Thrust belt
    12. 19. MTEM Global Operations Onshore Offshore
    13. 20. Land acquisition <ul><li>Surface conditions successfully operated in </li></ul><ul><ul><li>Farmland </li></ul></ul><ul><ul><li>Desert </li></ul></ul><ul><ul><li>Jungle </li></ul></ul><ul><ul><li>Plantation </li></ul></ul><ul><ul><li>Urban </li></ul></ul><ul><ul><li>Rice paddies </li></ul></ul><ul><ul><li>Muskeg </li></ul></ul><ul><ul><li>Open prairie </li></ul></ul><ul><ul><li>Beach / Littoral </li></ul></ul>
    14. 21. MTEM Hardware
    15. 22. Receiver station and battery Receiver box and battery in the line. Box with acquisition and telemetry electronics. Grounded with earth electrode.
    16. 23. Source Buggy and Unit Source buggy with generator and source unit. Source engineer with Zonge and control electronics.
    17. 24. Source Electrodes An array of 1 to 40 electrodes hammered into 80-100cm into the ground. Fenced off (3m) and manned when source cables are connected.
    18. 25. Source Safety system Source activation and emergency shut off at the source electrode array. Emergency shutoff cuts power to the entire system.
    19. 26. Source electrode transport Source electrode transport buggy. Low ground pressure buggy to transport the 40 electrodes per source pole location.
    20. 27. Land Operations
    21. 28. A Step Change in the use of EM Input Recording (combination of Earth and System Responses) Airwave Earth response
    22. 29. Impulse response - land Offset = 1 km Air Wave Earth Impulse Response
    23. 30. 1D model Source 1A.m Source Receiver (V) x = 1000m 500m 20 Ohm.m 500 Ohm.m Dx 25m
    24. 31. Impulse response Effect of fluid saturation Offset = 1 km
    25. 32. Impulse response – land Convolution with a system response Air Wave
    26. 33. Impulse response measurements Full Waveform Amplitudes Travel Time
    27. 34. Multi-Transient Theoretical PRBS In red Measured Signal In black
    28. 35. Deconvolution Input amps at source Output volts at receiver Deconvolved impulse response (ohms/m 2 /s)
    29. 36. Deconvolved Data – common offset Air Wave High peak amplitude and early arrival time indicate a resistor.
    30. 37. Data Processing Apparent resistivity Step Response Integration Peak picking Impulse Response
    31. 38. Inversion model and response Offset 1000m
    32. 39. Inversion model and response Offset 2000m
    33. 40. Inversion model and response Offset 2500m
    34. 41. Inversion model and response Offset 3000m
    35. 42. Inversion model and response Multi-offsets 2000m, 2500m and 3000m
    36. 43. Results summary 4 ways to detect hydrocarbons 2-D DC resistivity inversion Traveltime to resistivity mapping 1-D Occam Inversion 1800m Common offset section
    37. 44. What does MTEM provide <ul><li>Feasibility study – desktop </li></ul><ul><li>Feasibility study – field assessment </li></ul><ul><li>Survey design </li></ul><ul><li>Acquisition </li></ul><ul><li>Processing </li></ul><ul><li>Inversion </li></ul><ul><li>Technical/interpretation support </li></ul><ul><ul><li>3D modeling, advanced inversions </li></ul></ul>
    38. 45. Well Logs
    39. 46. 1D Modeling <ul><li>% difference in impulse response . </li></ul>
    40. 47. <ul><li>We take a collaborative approach with the client </li></ul><ul><li>Problem solving, asset-based </li></ul><ul><li>Oilfield services contractor </li></ul><ul><li>Support asset team with their interpretation and decisions </li></ul>How do we work? Top Reservoir from seismic
    41. 48. Multi-Transient EM
    42. 49. Inversion model and response Offset 1500m
    43. 50. Inversion model and response Offset 3500m