Seismic Reflection Processing and DHIs Quiz

Seismic Reflection Processing

• Filtering data is a common method used to remove noise and enhance the vertical resolution of seismic data.

• Seismic data is often contaminated by noise from various sources, including wind, traffic, and cultural noise, electrical signals, ocean waves, and motion.

• Frequency domain filters, such as high pass, low pass, band pass, and notch filters, are commonly used to remove noise from seismic data.

• Stacking seismic traces is another method used to reduce random noise and increase the signal-to-noise ratio.

• Common-mid(depth)-point (CMP) stacking is a method of summing signals from similar input channels to improve the signal-to-noise ratio.

• CMP stacking can be vertical or horizontal, with the fold (number of times the same point on a reflector is sampled) determined by the number of geophones and array spacing.

• Reflectivity and convolution are two factors that determine the seismic trace recorded in the field.

• Deconvolution (inverse filtering) is a method used to further remove noise from seismic traces and increase vertical resolution.

• Travel time curve is a hyperbola, but asymmetric where the axial plane is at x = -2hsinθ.

• Determining dip angle θ requires solving for travel time values from different geophone positions and distances.

• NMO correction is a method used to correct for the different travel times of reflected events for different geophone positions.

• Migration is a process used to move reflections back to their point of origin and restore seismic reflectors to their proper x-y position.Introduction to Seismic Surveying and Direct Hydrocarbon Indicators (DHIs)

• Dipping layers can be estimated using the formula Δtd = t2 - t1 ~ to (s sinθ /h) ~ 2s sinθ /V, where Δtd is dip moveout, s is distance, h is thickness, and θ is dip angle.

• Seismic surveying involves pre-migration, migrated stack, and seismic migration techniques to improve data/image quality.

• Seismic interpretation involves working from the top of the section towards the bottom to distinguish major reflectors and geometries of seismic sequences.

• DHIs (Direct Hydrocarbon Indicators) are anomalous seismic responses related to the presence of hydrocarbons, caused by the acoustic impedance of porous rock decreasing as hydrocarbon replaces brine in pore spaces.

• DHIs include amplitude anomaly, fluid contact reflection, and fit to structural contours.

• Oil sands have lower impedance than water sands and shales, and gas sands have lower impedance than oil sands.

• The larger the impedance difference between the HC sand and its encasing shale, the greater the anomaly.

• DHIs can be detected through techniques such as Amplitude Variation with Offset (AVO), which uses pre-stack seismic data to determine thickness, porosity, density, velocity, lithology, and fluid content of rocks.

• AVO analysis helps unravel lithology and fluid effects, especially at the top of a reservoir, by examining variations in amplitude with angle or offset.

• Maps or crossplots of AVO responses can be used to detect pore-fill anomalies, i.e. hydrocarbons, and map their lateral extent.

• AVO response is quantified in terms of two parameters: intercept (A) and slope (B).

• Seismic data can be used to estimate A and B, and to map the extent of gas-filled reservoirs using DHIs.

Seismic Reflection Processing

• Filtering data is a common method used to remove noise and enhance the vertical resolution of seismic data.

• Seismic data is often contaminated by noise from various sources, including wind, traffic, and cultural noise, electrical signals, ocean waves, and motion.

• Frequency domain filters, such as high pass, low pass, band pass, and notch filters, are commonly used to remove noise from seismic data.

• Stacking seismic traces is another method used to reduce random noise and increase the signal-to-noise ratio.

• Common-mid(depth)-point (CMP) stacking is a method of summing signals from similar input channels to improve the signal-to-noise ratio.

• CMP stacking can be vertical or horizontal, with the fold (number of times the same point on a reflector is sampled) determined by the number of geophones and array spacing.

• Reflectivity and convolution are two factors that determine the seismic trace recorded in the field.

• Deconvolution (inverse filtering) is a method used to further remove noise from seismic traces and increase vertical resolution.

• Travel time curve is a hyperbola, but asymmetric where the axial plane is at x = -2hsinθ.

• Determining dip angle θ requires solving for travel time values from different geophone positions and distances.

• NMO correction is a method used to correct for the different travel times of reflected events for different geophone positions.

• Migration is a process used to move reflections back to their point of origin and restore seismic reflectors to their proper x-y position.Introduction to Seismic Surveying and Direct Hydrocarbon Indicators (DHIs)

• Dipping layers can be estimated using the formula Δtd = t2 - t1 ~ to (s sinθ /h) ~ 2s sinθ /V, where Δtd is dip moveout, s is distance, h is thickness, and θ is dip angle.

• Seismic surveying involves pre-migration, migrated stack, and seismic migration techniques to improve data/image quality.

• Seismic interpretation involves working from the top of the section towards the bottom to distinguish major reflectors and geometries of seismic sequences.

• DHIs (Direct Hydrocarbon Indicators) are anomalous seismic responses related to the presence of hydrocarbons, caused by the acoustic impedance of porous rock decreasing as hydrocarbon replaces brine in pore spaces.

• DHIs include amplitude anomaly, fluid contact reflection, and fit to structural contours.

• Oil sands have lower impedance than water sands and shales, and gas sands have lower impedance than oil sands.

• The larger the impedance difference between the HC sand and its encasing shale, the greater the anomaly.

• DHIs can be detected through techniques such as Amplitude Variation with Offset (AVO), which uses pre-stack seismic data to determine thickness, porosity, density, velocity, lithology, and fluid content of rocks.

• AVO analysis helps unravel lithology and fluid effects, especially at the top of a reservoir, by examining variations in amplitude with angle or offset.

• Maps or crossplots of AVO responses can be used to detect pore-fill anomalies, i.e. hydrocarbons, and map their lateral extent.

• AVO response is quantified in terms of two parameters: intercept (A) and slope (B).

• Seismic data can be used to estimate A and B, and to map the extent of gas-filled reservoirs using DHIs.