Electromagnetic Survey Data Segmentation for Reservoir Detection
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Solution Overview
Problem
Current controlled-source electromagnetic (CSEM) survey techniques face challenges in distinguishing between different subterranean reservoir compositions, particularly due to ambiguity in interpreting data from thin resistive layers and large-scale background structures, leading to complex and costly survey methods with limited data quality.
Innovation Solution
The method involves analyzing electromagnetic field data from different source-receiver separations, using a threshold offset to differentiate between TE mode-dominated data for large-scale background strata and TM mode-dominated data for thin resistive/conductive layers, allowing for efficient processing using conventional magnetotelluric techniques for background information and CSEM techniques for layer identification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CSEM survey techniques are used to identify reservoirs, then the presence of hydrocarbon-bearing reservoirs can be detected, but the ability to distinguish between thin resistive layers and large-scale background structures is poor
Solution Approach 1:
The patent segments the electromagnetic field data into two distinct datasets based on source-receiver separation distance: a first dataset for near offsets (less than threshold) sensitive to thin resistive/conductive layers, and a second dataset for far offsets (greater than threshold) sensitive to large-scale background structures. This segmentation allows independent processing and interpretation of each dataset to resolve the ambiguity between thin layers and background structures.
Solution Approach 2:
The patent applies different processing techniques to different portions of the data based on their local characteristics. The first dataset (near offsets) is processed using techniques optimized for detecting thin layers, while the second dataset (far offsets) is processed using techniques optimized for characterizing background structures. This local quality approach ensures that each data portion is analyzed with the most appropriate method.
2Loss of information
If multiple survey techniques are employed to obtain both thin layer and background structure data, then comprehensive information can be obtained, but the survey becomes more complex and costly
Solution Approach 1:
The patent makes the single CSEM survey system multi-functional by showing that one survey collects both types of data needed for comprehensive interpretation. The same electromagnetic survey apparatus collects near-offset data for thin layer detection and far-offset data for background structure characterization simultaneously, eliminating the need for separate survey systems.
Solution Approach 2:
The patent segments the data collection process into two functional components within a single survey: near-offset measurements for thin layer detection and far-offset measurements for background structure analysis. This segmentation is achieved through data processing rather than requiring separate physical surveys, reducing overall system complexity.
3Loss of information
If data from both thin layers and background structures are collected using standard CSEM, then comprehensive information is available, but the signal-to-noise ratio is reduced
Solution Approach 1:
The patent segments the electromagnetic field data into near-offset and far-offset datasets, allowing each segment to be processed with techniques optimized for its specific geological target. This segmentation preserves signal integrity by applying appropriate processing to each data portion, thereby maintaining high signal-to-noise ratios for both thin layer detection and background structure characterization.
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 enables more efficient and cost-effective data collection by providing complementary data sets without the need for complex tow paths or specialized receivers, improving signal-to-noise ratios and allowing for accurate characterization of subterranean resistivity profiles.
Implementation Method 1
CSEM techniques involve transmitting an EM signal into the seafloor, generally using a horizontal electric dipole (HED) source (transmitter), and measuring the response at EM receivers (detectors) for a range of distances from the source
Implementation Method 2
the highly conducting seawater attenuates the component of the EM signal passing through the reservoir more than would be the case if the reservoir contained hydrocarbon
Data Source
AI summary
A method of analysing results from an electromagnetic survey of an area that is thought or known to contain a subterranean resistive or conductive body within a background strata configuration is described. The method comprises providing a set of electromagnetic field data obtained using at least one electromagnetic receiver and at least one electromagnetic source for a range of source-receiver separations, e.g. providing conventional controlled-source electromagnetic survey data. A subset of the electromagnetic field data is identified that comprises data obtained for source-receiver separations greater than a selected threshold offset. The threshold offset is chosen so that data beyond this offset are characteristic of magnetotelluric data. Thus the subset of data is then processed in accordance with a first technique to obtain information on the background strata configuration. Other electromagnetic field data obtained for source-receiver separations less than the threshold offset may then be processed in accordance with a second technique to obtain information on any subterranean resistive or conductive body within the background strata configuration.