Induction Log Borehole Correction via Effective Formation Conductivity
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Solution Overview
Problem
Electromagnetic induction well logging instruments face challenges in accurately determining formation conductivities due to the effects of wellbore fluids and conductivity variations, requiring effective borehole correction methods to isolate formation conductivity from wellbore influences.
Innovation Solution
A method to estimate effective formation conductivity using measurements from an induction receiver proximate to the transmitter, allowing for correction of apparent conductivity measurements by subtracting the borehole-related contribution, effectively replacing the wellbore with a homogeneous medium of similar conductivity, using iterative calculations and pseudo-geometrical factors to account for wellbore effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If borehole correction is performed using traditional linear equations or true inversion methods, then measurement precision is improved, but device complexity and calculation complexity increase significantly
Solution Approach 1:
The patent introduces the concept of effective formation conductivity as a simplified parameter that consolidates multiple complex parameters (formation conductivity, wellbore conductivity, tool standoff) into a single equivalent parameter. This parameter change enables the use of simpler linear correction equations while maintaining measurement accuracy, resolving the contradiction between precision and complexity.
Solution Approach 2:
The patent extracts and separates the borehole effect contribution from the total measured conductivity signal. By identifying and removing the specific borehole-related component (σb) from the apparent conductivity measurement, the method isolates the formation conductivity signal while using simplified correction procedures rather than complex full-inversion methods.
2Measurement precision
If iterative calculations are used to determine effective formation conductivity, then measurement precision is improved, but loss of time increases due to multiple calculation steps
Solution Approach 1:
The patent performs preliminary calculations to establish lookup tables containing pre-computed pseudo-geometrical factors for various tool standoffs and formation conductivities. During actual logging operations, the correction process simply requires table lookup and interpolation rather than full iterative calculation, significantly reducing computation time while maintaining precision.
Solution Approach 2:
The patent implements a hybrid approach where a limited number of iterative steps (typically 2-3 iterations) are performed to converge on the effective formation conductivity, rather than performing exhaustive iterative calculations. This partial iteration approach achieves sufficient precision for practical applications while minimizing time loss.
3Ease of operation
If the pseudo-geometrical factor is assumed independent of surrounding media conductivities, then ease of operation is improved, but measurement precision deteriorates
Solution Approach 1:
The patent applies different levels of complexity to different aspects of the correction process. The pseudo-geometrical factor is treated as locally dependent on tool standoff distance but independent of formation and wellbore conductivities for practical purposes. This localized simplification maintains ease of operation while preserving sufficient precision for most logging applications.
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
This approach enhances the accuracy of conductivity measurements by isolating formation conductivity from wellbore influences, providing reliable data for hydrocarbon detection and improving the precision of borehole correction procedures.
Implementation Method 1
Electric current is passed through the transmitter to induce electromagnetic fields in the formations surrounding the wellbore. Voltages are induced in the receiver as a result of the currents induced in the formation.
Data Source
AI summary
A method for correcting induction conductivity well log measurements for conductivity of a wellbore and a formation proximate the wellbore includes estimating an effective formation conductivity for the formation proximate the wellbore from measurements made by an induction receiver proximate an induction transmitter. The effective formation conductivity is used to correct apparent conductivity measurements made by at least one induction receiver on the instrument.