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On the use of different methods for estimating magnetic depth

Fugro-LCT, Houston, Texas, U.S.

Corresponding author: xli@fugro.com

The first 20% of the full text of this article appears below.

Magnetic depth estimation plays an important role in magnetic interpretation. A complete quantitative interpretation of potential fields data aims to estimate three types of information about sources of geologic interest: the depth, the dimension, and the contrast in the relevant physical property. Such an interpretation suffers from inherent ambiguity. It is impossible to obtain all three types of information simultaneously without other a priori information. In many applications, we are often interested in depth more than either dimension or physical property contrast. Thus, different quick methods have been developed, over half a century, to estimate the magnetic depth. These methods work for simplified source geometries (dimensions) and are independent of the susceptibility contrast. The depths estimated by some method can be used as the final, quantitative solution in some ideal situations—i.e., the anomaly is well isolated and the noise is insignificant or well removed. It is more often that estimated depths provide a good starting point for a genuine structural interpretation (e.g., an interactive modeling or a constrained inversion).

In petroleum exploration, for example, the structural surface interpreted from magnetic depth estimates is often the best available approximation to the true crystalline (i.e., metamorphic/igneous) basement configuration. Basement depth (or equivalently, sedimentary thickness) is a primary exploration risk parameter. Estimates of basement depth are directly applicable to basin modeling (e.g., source rock volume estimation) and thermal maturity applications (e.g., source-rock burial-depth). Basement structure inferred from magnetic depth estimates provides insight into the evolution of more recent sedimentary features (e.g., sub/minibasin compartmentalization, salt structure distribution/kinesis, localization of reservoir-bearing structures) in areas where the inherited basement fabric/architecture has affected (either continuously or episodically) basin evolution and development. Examples of the latter are the prolific, passive rifted margins of the southern Atlantic Ocean. A basin's "plumbing" often exploits faults and fractures within the sedimentary . . . [Full Text of this Article]