Hoa Truong
Mind Map by Hoa Truong, updated more than 1 year ago
Hoa Truong
Created by Hoa Truong over 6 years ago


Seismic reflection survey

Resource summary

    1. minimises subsurface mapping risk away from hard data locations (wells)
      1. acoustic imaging of the subsurface in 2way time
        1. Acoustic pulse is partially transmitted+ reflected at boundaries betw. rocks with different acoustic impedence
          1. complicated extension of echo (water depth) sounder
            1. source emit sound down through earth- interfaces where impedance changes partially reflect sound up-record- reflection strength determined by difference acoustic impedence (Z) across interface.
              1. reflection coefficient determine amplitude of reflected wave
                1. move device in a line produce 2D mapping, in a grid produce 3D mapping. difficult to move device-3D is provide by many closely-space receivers in grid.
                2. Depth resolution
                  1. poor relative to log+other well data (spatial/geographic resolution). typical range: quarter to half wavelenth
                    1. size of smallest distinguishable features in the data
                    2. Steps
                      1. 1. Acquisition
                        1. survey is designed+shot
                          1. compositions
                            1. source of sound
                              1. air guns (marine)
                                1. vibroseis truck (land)
                                  1. frequency range: 8-80Hz
                                2. receiver detect returning echo
                                  1. geophones (land)
                                    1. hydrophones (marine)
                                    2. amplify, digitise, record data instruments
                                    3. Cheaper in sea (equipment loaded on boat, operate day+night) than land (manual load equipments, electric cables)
                                    4. 2. Processing
                                      1. intensive computer processing-image from seismic data
                                        1. data pass through separate processes, different purposes
                                          1. Random noise suppression
                                            1. improve signal:sound
                                              1. Common Midpoint Shooting (CMP)
                                                1. data shot so many reflections record from same point-reflections add together- make stack section- better signal-noise ratio than original data
                                                  1. CMP gathers: raw, recorded shot records. not easy integret
                                                  2. combine CMPs -transform to geologically meaningful display that can be integret
                                                    1. Velocity Analysis for correcting Normal Moveout (NMO)
                                                      1. Stacking (summing) NMO-corrected CMP gathers - attenuate noise- improve S:N ratio
                                                        1. Range of possible S:N improvement
                                                        2. Coherent noice (multiples)
                                                          1. Resolution enhancement
                                                            1. better resolution -more detail image
                                                            2. Migration of received acoustic energy to correct reflector location
                                                              1. migration moves reflection to accurate location
                                                                1. when beds are not horizontal-reflections different from vertical receiver-distorted view of structure on seismic section
                                                                  1. distortion increase with deep, dip, velocity
                                                            3. 3. Intepretation
                                                              1. image is interpreted from seismic data- maps, geological models of subsurface
                                                                1. to define explotation + development well locations
                                                                  1. Good integretation: internally consistent with available well data+ basic geological concepts
                                                                    1. Basic procedures
                                                                      1. picks significant events+ faults in each seismic section
                                                                        1. time+ amplitude of each event is recorded
                                                                        2. mapping stratigraphic features
                                                                          1. predict environments of deposition +rock types from reflection pattern
                                                                          2. mapping reservoir properties
                                                                            1. porosity map (well data)
                                                                              1. seismic event amplitude at reservoir level correlation with porosity
                                                                                1. transform seismic amplitude - more detailed porosity map
                                                                                2. mapping pore fluids
                                                                                  1. dept conversion
                                                                                    1. calculate depth from seismic times. requires velocity from well/seismic data
                                                                                  2. Key intepretable features
                                                                                    1. seismic profile section
                                                                                      1. seismic horizons (coherent reflection events)
                                                                                        1. faults (displaced coherent events
                                                                                          1. 3D better than 2D
                                                                                            1. provide a volume of data
                                                                                              1. view in any orientation
                                                                                                1. able to see channels from origin
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