Method and system for detecting hydrocarbon reservoirs using statistical normalization of amplitude-versus-offset indicators based upon seismic signals

A digital computing system for analyzing seismic survey signals to identify 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 gathers of seismic signals, each seismic survey signal obtained from a detector located at the earth responsive to seismic energy imparted to the earth, each gather corresponding to a plurality of seismic signals reflected from depth points below one of a plurality of surface locations at varying angles of incidence;
• a graphics output device;
• and
• a programmed computer, coupled to the memory and to the graphics output device, for:
• retrieving, from the memory, digital data corresponding to a plurality of gathers;
• determining, for each depth point represented in each of the gathers, an AVO intercept value and an AVO gradient value;
• selecting a plurality of surrounding depth points surrounding an analysis depth point in space and in time;
• deriving a background trend of the AVO intercept values and AVO gradient values for the plurality of surrounding depth points;
• determining a raw indicator corresponding to the AVO intercept value and the AVO gradient value for the analysis depth point;
• evaluating a probability function for the background trend of the AVO intercept values and AVO gradient values for the plurality of surrounding depth points;
• modifying the raw indicator for the analysis depth point using the results of the step of evaluating a probability function to produce a modified indicator;
• storing the modified indicator in memory for the analysis depth point;
• repeating the selecting, deriving, determining, evaluating, modifying, and storing steps for a plurality of analysis depth points;
• and
• communicating the values of the modified indicators for the plurality of analysis depth points to the output device.

A computer-readable memory having a storage medium configured so that, when read and used by a computer, the computer is directed to distinguish the presence of hydrocarbon-bearing formations in a region of the earth corresponding to the seismic survey signals, wherein the seismic survey signals comprise a plurality of gathers of time-based seismic survey signals obtained at a plurality of detectors at the earth responsive to seismic energy imparted to the earth, 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 the analysis depth point in space and in time;
• deriving a background trend of the AVO intercept values and AVO gradient values for the plurality of surrounding depth points;
• determining a raw indicator corresponding to the AVO intercept value and the AVO gradient value for the analysis depth point;
• evaluating a probability function for the background trend of the AVO intercept values and AVO gradient values for the plurality of surrounding depth points;
• modifying the raw indicator for the analysis depth point using the results of the step of evaluating a probability function to produce a modified indicator;
• and
• storing the modified indicator in memory;
• and
• displaying the values of the modified indicators for the plurality of analysis depth points on an output device.