Borehole-to-Surface EM Survey Separating Near-Surface Anomalies
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Solution Overview
Problem
Existing electromagnetic survey methods face challenges in accurately discriminating between resistivity anomalies at depth and those near the surface, particularly in time-lapse monitoring, due to the influence of weather events and the proximity of sensors to the earth's surface, which complicates the evaluation of subsurface features like hydrocarbon reservoirs.
Innovation Solution
The use of a borehole-to-surface electromagnetic survey apparatus that injects electrical current through strategically positioned electrodes, both within the borehole and at the surface, allows for the separation of near-surface anomalies from subsurface features by processing electromagnetic fields to isolate and remove distortive effects, enabling more accurate measurement of subsurface resistivity variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If electromagnetic sensors are deployed at the surface to measure subsurface resistivity, then the measurement depth can reach deep formations, but the measurement precision deteriorates due to contamination from near-surface resistivity anomalies
Solution Approach 1:
The patent introduces a borehole as an intermediary medium between the surface sensors and deep subsurface formations. The borehole provides a controlled access path that allows electromagnetic fields to penetrate to deep targets while isolating the measurement process from near-surface resistivity anomalies. The borehole environment serves as a mediator that separates the sensor array from harmful surface effects while maintaining connection to deep formations.
Solution Approach 2:
The patent transitions from purely surface-based two-dimensional measurements to three-dimensional measurements by deploying sensors both at the surface and within the borehole at various depths. This dimensional extension allows the system to differentiate between near-surface and deep subsurface resistivity variations, enabling accurate deep formation measurements while accounting for surface effects through multi-level data collection.
2Reliability
If time-lapse monitoring is performed with surface sensors, then temporal changes in subsurface resistivity can be detected, but the reliability deteriorates due to weather events affecting surface measurements
Solution Approach 1:
The borehole serves as a protected intermediary environment that shields the measurement system from weather events during time-lapse monitoring. By positioning sensors within the borehole rather than directly at the surface, the system maintains consistent measurements over time while being isolated from rainfall, temperature variations, and other atmospheric conditions that would otherwise contaminate the data.
3Area of stationary object
If multiple electrode configurations are used to probe different lateral regions, then the survey coverage area increases, but the device complexity increases
Solution Approach 1:
The patent employs a multi-functional electrode system where the same borehole electrode can serve multiple purposes by being paired with different surface electrodes or counter-electrodes. This universal electrode design allows a single downhole electrode to probe different lateral regions when combined with various surface electrode configurations, thereby achieving extensive survey coverage without proportionally increasing the number of downhole components.
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 subsurface feature evaluation by effectively separating near-surface resistivity variations from those of interest at greater depths, improving the reliability of resistivity measurements and reducing errors caused by surface anomalies, thus providing clearer insights into formation properties.
Implementation Method 1
an electrical field produces electrical currents in the earth that have an associated magnetic field, and a time-varying magnetic field induces electrical currents that result in an electrical field
Implementation Method 2
The distribution of electric current flow produced by an EM source is determined by the three dimensional resistivity distribution within the earth
Data Source
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AI summary
Errors produced in a borehole to surface electromagnetic (BSEM) survey by near surface electrical anomalies on the estimates of formation properties are reduced. The effects of variations in subsurface electrical resistivity near the surface are separated from electrical resistivity changes at locations in the formations of interest far from the measurement region. A survey system includes one or more electrodes to inject electrical current at formation depth within a borehole, one or more counter electrodes which collect such current on the surface of the earth, and one or more electrodes to inject current on the surface. A transmitter is selectively connectable to different sets of the electrodes to cause a current to flow between the selected electrode sets. The resultant fields from the current flow are sensed and processed. The effects of near surface anomalies are detectable in the data and removable from the survey data of interest regarding the formations. The survey data more accurately indicates formation features or properties of interest.