System and method of petrophysical formation evaluation in heterogeneous formations

A method of estimating the position of beds in a layered geological formation using a plurality of wireline measurement logs obtained from a plurality of wireline tools, comprising the steps of:

• building a response model for each of said wireline tools, where said response model predicts a wireline measurement log based on a description of bed boundary positions in the formation;
• inputting a common description of bed boundary positions to each response model;
• outputting a predicted log from each of said response models based on said common description of bed boundary positions;
• comparing said predicted logs with said measurement logs and determining a difference error between said logs;
• and
• inputting another common bed boundary description and repeating said outputting and comparing steps for said other common bed boundary description.

A geological formation interpretation system comprising a specially programmed computer having:

• memory means for storing a plurality of actual measurement logs of a geological formation;
• memory means for storing one or more tool response models where each response model predicts a measurement log based on a formation description;
• means for inputting a first formation description and a second formation description;
• processor means for
• generating a first predicted log based on the first input formation description and said tool response model,
• for comparing the first predicted log with a corresponding actual measurement log,
• for generating a first difference error from the comparison of the first predicted log and the actual measurement log,
• for generating a second predicted log based on the second input formation description and said tool response model,
• for comparing the second predicted log with a corresponding actual measurement log, for generating a second difference error from the comparison of the second predicted log and the actual measurement log,
• for determining a lesser of the first error difference and the second error difference;
• and
• display means for communicating the formation description which yielded the lesser error difference.

A method of estimating the geometry and properties in a zoned geological formation using one or more measurement logs obtained from one or more tools traversing an oilwell borehole having a number of depth intervals, comprising the steps of:

• building a formation description of homogeneous horizontal layers;
• inputting said formation description for a plurality of depth intervals to a set of linear response models for said tools, where said response model predicts a measurement log based on a description of bed boundary positions in the formation;
• comparing an output predicted log with said measurement log and determining a difference error between said logs;
• repeatedly adjusting said formation description to minimize said difference error;
• for one or more depth intervals, adjusting respective formation descriptions by introducing radial zone boundaries corresponding to the positions of fluid fronts in invaded zones;
• repeatedly adjusting the invaded zone boundaries to minimize said difference error;
• for one or more depth intervals, adjusting respective formation descriptions by evidence of formation dip or inclination based on dip measuring tools.