By: Maggie Baber, NEOS Geoscientist
Magnetic interpretation is an integral component of NEOS’s multi-measurement interpretation methodology (MMI). Magnetic data measures changes in a rock’s magnetic susceptibility, or the degree of magnetization in response to earth’s magnetic field. Rocks or materials with high magnetite content have a high magnetic susceptibility.
Magnetics, along with gravity and other MMI measurements, is used to better understand subsurface geology and can assist in mapping faults, folds, lithology changes, intrusions, and mineral deposits in the Earth’s upper crust. NEOS also uses magnetic data to observe changes in basement composition that may be linked to production in overlying shales.
But the application of magnetic data isn’t restricted to subsurface investigation: NEOS takes our magnetic interpretation one step further by interpreting surface and near-surface magnetics to find abandoned wellbores.
Abandoned wellbores, many of which are not logged in public records, pose a serious environmental threat: Wells that have not been properly sealed can leak methane to the surface and damage vegetation, contaminate water, and/or trigger explosions. The EPA estimates there are 1.2 million abandoned wellbores in the United States, many of which are decades old. Of those, 200,000 exist in Pennsylvania alone.
NEOS reduces the impact of abandoned wells on current drilling operations and supports environmentally sound operations by identifying, mapping, and characterizing these features for our clients. This method is especially useful in areas of high well density, where a wellbore may be forgotten in years since operation, as well as in densely forested areas, where wellbores may be hidden by trees.
To locate abandoned wells the NEOS methodology uses airborne acquired high resolution magnetic data. Via data processing, NEOS separates the magnetic signal into two products. The first is a low frequency ‘geologic magnetic’ grid or magnetic signal sourced from the geology alone. It is used to map subsurface geology and observe changes in basement lithology, but it is not useful in determining locations of objects on or near the surface.
The second product, the high frequency ‘cultural magnetic’ grid, is magnetic signature sourced solely from near surface objects. We use this grid to locate and categorize surface or near surface objects with high susceptibility, including abandoned wells.
Most magnetic anomalies we see on this ‘cultural’ grid are associated with known features, such as wells, pipelines, bridges, houses, and other mapped sources of magnetic susceptibility. We check each anomaly using mapped cultural data and satellite images and separate each anomaly into categories.
All remaining, unidentifiable point-sources we categorize as unknown magnetic material and potentially may be abandoned wells.
In a roughly 2000 square mile neoBASIN study of the Appalachian Basin in northwestern Pennsylvania, NEOS identified 9 untagged wells and 21 unknown sources, assumed to be abandoned wells or abandoned magnetic material, for our client.