Method and system for detecting hydrocarbon reservoirs using amplitude versus offset analysis of seismic signals

A computer-readable memory having a storage medium configured so that, when read and used by a computer, the computer is directed to analyze seismic survey signals comprising a plurality of series of time-based signals obtained at a plurality of detectors at the earth responsive to seismic energy imparted to the earth and gathered into gathers of seismic survey signals, each gather representative of energy reflected from depth points below a corresponding one of a plurality of surface locations at a plurality of angles of incidence, said computer directed by a plurality of operations comprising:

• retrieving, from a memory, digital data corresponding to a plurality of gathers;
• determining, for each depth point represented by each of the gathers, an AVO intercept value and an AVO gradient value;
• for each of a plurality of analysis depth points, operating the computer to perform the steps of:
• selecting a plurality of surrounding depth points that surround, in space and in time, the analysis depth point;
• deriving a background trend of the AVO intercept values and AVO gradient values for the plurality of surrounding depth points;
• determining an indicator corresponding to the rate of change of the product of the AVO intercept value and the AVO gradient value for the analysis depth point, along the direction of a deviation vector of the AVO intercept value and the AVO gradient value from the background trend;
• and
• storing the indicator in memory;
• and
• displaying the values of the indicators for the plurality of analysis depth points on an output device.

A digital computing system for analyzing seismic survey signals to distinguish the presence of hydrocarbon-bearing formations in a region of the earth corresponding to the seismic survey signals, comprising:

• a memory for storing data corresponding to a plurality of series of time-based signals obtained at a plurality of detectors at the earth responsive to seismic energy imparted to the earth and gathered into gathers of seismic survey signals, each gather representative of energy reflected from depth points below a corresponding one of a plurality of surface locations at a plurality of angles of incidence;
• a graphics display output device;
• and
• a programmed computer, coupled to the memory and to the graphics display output device, for:
• retrieving, from the memory, digital data corresponding to a plurality of gathers;
• determining, for each depth point represented by each of the gathers, an AVO intercept value and an AVO gradient value;
• for each of a plurality of analysis depth points, performing the operations of:
• selecting a plurality of surrounding depth points that surround, in space and in time, the analysis depth point;
• deriving a background trend of the AVO intercept values and AVO gradient values for the plurality of surrounding depth points;
• determining an indicator corresponding to the rate of change of the product of the AVO intercept value and the AVO gradient value for the analysis depth point, along the direction of a deviation vector of the AVO intercept value and the AVO gradient value from the background trend;
• storing the indicator in the memory;
• and
• forwarding, to the graphics display output device, the values of the indicators for the plurality of analysis depth points for display.