Core Sample Resistivity Measurement for Rapid Exponent Calibration
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Solution Overview
Problem
Conventional methods for determining the cementation and saturation exponents of core samples from petroleum reservoirs are time-consuming, typically taking 4-6 weeks, which delays the evaluation of oilfield reservoir properties.
Innovation Solution
A method involving the preparation of brine, flushing the core sample, and determining resistivity indices to establish a function describing the dependency of true resistivity on saturation, allowing for the estimation of saturation and cementation exponents, thereby accelerating the calibration of electrical logs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional methods are used to determine cementation and saturation exponents, then measurement precision is maintained, but time consumption increases significantly (4-6 weeks)
Solution Approach 1:
The patent performs preliminary flushing of the core sample with brine to establish initial saturation conditions before measurements begin. This preliminary action prepares the sample in a controlled state, enabling faster subsequent measurements while maintaining accuracy by ensuring consistent starting conditions for the resistivity-saturation relationship determination
Solution Approach 2:
The conventional 4-6 week process is segmented into distinct phases: brine preparation and flushing, initial resistivity measurement at known saturation, functional relationship determination, and exponent calculation. By segmenting the process and identifying which steps are essential for precision versus those that can be expedited, the patent reduces overall time while preserving measurement accuracy
2Productivity
If rapid determination methods are implemented, then productivity increases, but measurement precision may deteriorate
Solution Approach 1:
The method uses the core sample itself to provide the brine saturation through flushing, eliminating the need for external saturation equipment or complex saturation procedures. The sample's own pore structure facilitates the brine displacement, and the electrical resistivity measurements automatically provide the data needed for exponent calculation, making the process self-contained and rapid while maintaining precision
Solution Approach 2:
The patent changes the saturation parameter by flushing the core sample with brine to achieve known saturation levels (Sw1, Sw2, etc.), then measures corresponding resistivity values. By systematically varying saturation and measuring resistivity, the method rapidly establishes the functional relationship Rt=f(Sw) and calculates exponents without requiring lengthy conventional procedures, thus increasing productivity while preserving measurement precision through controlled parameter variation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables rapid determination of essential exponents for calibrating electrical logs, providing data even before wellbore completion and allowing comparison with post-cleaning electrical properties to assess wettability effects.
Implementation Method 1
flushing the core sample with the brine
Implementation Method 2
determining a first true resistivity Rt1 at a first saturation Sw1... determining a function Rt=f(Sw) describing the dependency of the true resistivity Rt of the core sample and the saturation Sw
Data Source
AI summary
A method for determining the electrical properties of a core sample having an initial saturation Sw0, an initial true resistivity Rt0, and a porosity ϕ, including the steps: preparing a brine having a resistivity Rw, flushing the core sample with the brine, determining a first true resistivity Rt1 at a first saturation Sw1, once the resistivity Rw of the brine going into the core sample is the same as the resistivity Rw of the brine going out of the core sample, determining a function Rt=f(Sw) describing the dependency of the true resistivity Rt of the core sample and the saturation Sw in the core sample, based on the initial saturation Sw0, initial true resistivity Rt0, first true resistivity Rt1, and first saturation Sw1, second true resistivity Rt2, and first saturation Sw2, determining the resistivity Ro of the fully saturated core sample by estimating the function Rt=f(Sw) to full saturation of the core sample at Sw=100%, determining a resistivity indexIR=RtRoat the Sw, Sw1, Sw2 determining a saturation exponent n using linear regression of the log-log plot of IR vs. Sw.