Imaging mining hazards within coalbeds using prestack wave equation migration of in-seam seismic survey data: A feasibility study with synthetic data

Gas and water accumulations in old mine workings, voids and fault zones are threats to safety in coal mining. There are a variety of measures that can be taken to extract fluids prior to, or during mining; therefore, the ability to locate geological structures and old abandoned working and voids which may not have been mapped accurately are the key to overall success. However, current techniques are of limited use because of either high cost or low resolution. We simulate and evaluate use of high-frequency seismic data acquired in an in-seam geometry through the use of synthetic two-component elastic data for 2-D models. Elastic common-source seismic data collected at the mining coalface contain body waves reflected at coalbed interfaces such as faults and old workings. Reverse-time prestack elastic migration is used to image the interfaces. Numerical tests on synthetic data indicate that this approach is expected to be effective to detect abandoned mining workings containing different fluids (such as water or gas/air) and faults. However, the use of this approach is restricted to the nearest in-seam interface from the mine face. The three items that are new in this paper are (1) the application of wave equation migration to in-seam data, (2) use of a multiplicative (data derived) mask to enhance the migrated image, and (3) the demonstrated potential to distinguish fluids in mine voids from seismic data.