Reservoir Parameter Determination Using Resistivity Heterogeneity
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Solution Overview
Problem
Existing methods for interpreting well logging data in carbonate reservoirs are inadequate for accurately predicting hydrocarbon producibility due to the complexity of carbonate rock texture and pore structures, particularly in determining the cementation factor and porosity exponent, which significantly impacts water saturation estimates.
Innovation Solution
A method that determines the effect of formation porosity on resistivity by using resistivity maps to calculate a heterogeneity measure, transforming it into an algebraic term that adjusts the cementation factor, allowing for a depth-dependent log of cementation values and improved saturation calculations using Archie's law.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If fixed values for Archie's exponents (m and n) are used in mathematical relations, then the calculation process is simplified, but the accuracy of water saturation estimates deteriorates due to the heterogeneous pore structure of carbonate rocks
Solution Approach 1:
The patent transforms fixed Archie's exponents into depth-dependent dynamic values by using resistivity maps to calculate heterogeneity measures. The cementation factor m becomes a function of depth, varying with the resistivity heterogeneity of different formation layers, allowing the model to adapt to the heterogeneous pore structure of carbonate rocks while maintaining computational feasibility.
Solution Approach 2:
The patent changes the parameter values of Archie's exponents from fixed constants to variable parameters that depend on resistivity heterogeneity. By calculating heterogeneity measures from resistivity maps and transforming them into algebraic terms, the exponents m and n become depth-dependent parameters that reflect the actual geological conditions at different depths.
2Measurement precision
If laboratory core tests are used to determine Archie's exponents, then the values can be obtained from direct measurements, but the method cannot be applied to downhole formations of similar type and locations without extrapolation
Solution Approach 1:
The patent enables the logging tools themselves to determine the Archie's exponents by using the resistivity maps generated during the logging process. The tools calculate heterogeneity measures directly from the measured resistivity data, eliminating the need for separate laboratory core tests and allowing direct determination of exponents for the specific downhole formation being logged.
Solution Approach 2:
The patent replaces the mechanical/lab-based approach of core tests with an electromagnetic field-based approach using resistivity mapping. By substituting physical core analysis with electromagnetic measurements and image processing, the method can be applied directly to downhole formations without requiring physical core samples.
3Adaptability or versatility
If minor variations in the value of m and n are used, then the calculation is more flexible, but the estimate of water saturation becomes significantly impacted
Solution Approach 1:
The patent introduces a feedback mechanism where the calculated heterogeneity measure from resistivity maps is used to determine the cementation factor m, which then feeds back into the water saturation calculation. This feedback loop ensures that the exponents are consistently determined from the actual resistivity data, providing both flexibility to adapt to different formations and precision through self-consistent calculations.
Data Source
AI summary
A method of determining the effect of formation porosity on formation resistivity and parameters derived from the formation resistivity is described, including the step of determining for a depth interval a heterogeneity measure; and using a pre-defined relation to transform the heterogeneity measure into an algebraic term determining the effect of the formation porosity on the formation resistivity, based for example on Archie's law or similar relations.