Surface Electromagnetic Survey Anisotropy Estimation
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Solution Overview
Problem
Current hydrocarbon exploration techniques, such as electromagnetic and seismic surveys, fail to adequately account for resistive anisotropy in the subsurface, leading to errors in reservoir identification and hydrocarbon saturation determination due to non-uniqueness of inversion models and insufficient consideration of anisotropy in overburden structures.
Innovation Solution
A methodology that estimates macro and intrinsic anisotropy of the overburden during surface electromagnetic surveys, using tools like the PeriScope™ and RtScanner™, to constrain the inversion model and improve the accuracy of resistivity measurements, allowing for better localization of reservoirs and hydrocarbon saturation assessment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electromagnetic survey inversion is performed without accounting for anisotropy, then the survey can be conducted with simpler processing, but the inversion results contain substantial errors due to non-uniqueness and failure to account for resistive anisotropy
Solution Approach 1:
The patent applies preliminary action by estimating macro and intrinsic anisotropy parameters before performing the full electromagnetic inversion. This pre-estimation step provides initial constraints on the inversion model, reducing the non-uniqueness problem and improving convergence to accurate solutions without requiring complex anisotropic modeling throughout the entire inversion process
Solution Approach 2:
The patent changes parameters by introducing anisotropy estimates (macro and intrinsic) as additional constraints in the inversion model. These parameter estimates are derived from the electromagnetic data itself and are used to modify the inversion approach, transforming it from a standard isotropic inversion to one that accounts for anisotropic subsurface properties
2Loss of information
If seismic surveys are used to measure acoustic response, then subsurface structure and layering can be identified, but the surveys cannot discriminate between liquid types or identify gas saturations due to similar acoustic propagation
Solution Approach 1:
The patent merges electromagnetic survey data with seismic survey data to compensate for the limitations of each individual method. While seismic provides structural information, electromagnetic surveys provide resistivity information that varies significantly between fluid types, allowing combined interpretation to distinguish between hydrocarbons, water, and gas saturations that seismic alone cannot differentiate
3Reliability
If other measurement techniques are used to understand subterranean structures, then additional data can be collected, but they also fail to sufficiently account for anisotropy of the overburden
Solution Approach 1:
The patent performs preliminary estimation of macro and intrinsic anisotropy from the electromagnetic data before using these estimates to constrain the inversion. This approach accounts for overburden anisotropy without requiring complex additional measurement systems, as the anisotropy parameters are derived directly from the electromagnetic survey responses
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 precision of hydrocarbon exploration by providing accurate estimates of horizontal and vertical resistivity, layer dip, and anisotropy, reducing errors in reservoir identification and improving the delineation of subterranean structures, thereby increasing the effectiveness of hydrocarbon surveys.
Implementation Method 1
controlled source electromagnetic surveys are used to help confirm the presence of a resistive fluid
Implementation Method 2
the resistivity of reservoirs below the ground surface or seafloor has been detected
Data Source
AI summary
A technique provides a methodology for improving surveys of subterranean regions. The methodology comprises estimating macro anisotropy and an intrinsic or micro anisotropy of an overburden. A surface electromagnetic survey is conducted, and the data from the survey is inverted based on or including information gained from estimating the macro anisotropy and/or intrinsic anisotropy. A processor system can be used to conduct the inversion with the adjustments for anisotropy to improve the information provided by the survey.