1. Introduction
Oil shale in Jinhe Coal Mine was formed in the Mesozoic Jurassic and Middle Jurassic. The main geological problems encountered were faults. Combined with the disclosure, how to further determine the development position and extension length of the faults in the working face is one of the big constraints and problem for safe mining.
2. Treatment solution
In-seam seismic transmission detection method was used to detect the structure of the oil shale. Shot points and geophones were arranged in the oil shale layer. Propagation characteristics of the transmitted seismic waves were used to detect the structure inside the working face.
Figure 1 Schematic diagram of transmitted in-seam wave seismic exploration
3. Work situation
Shot points and geophones were arranged along the head entry, interconnection and tail entry of the working face. Distance between adjacent shot points was 10 m while the distance between the adjacent geophones was 20 m. A total of 60 effective single shot records were obtained.
Fig 2 Layout drawing of in-seam wave detection project (
shot points, geophones)
4. Achieved accomplishment
Fig. 3 CATA imaging of the in-seam seismic exploration in working face16114
Two faults (CF1, CF2) were found in the working face after explaining from the received data. The fault distance was larger than 1/2 oil shale thickness. The strike and extension length of the faults were determined. No other geological anomalies were found. The detection effect was verified by mining.
5.FAQ
Q1: Why is the in-seam seismic exploration suitable for structural detection of the oil shale layers?
A: In oil-bearing shale formations, oil shale has the characteristics of the velocity and the density lower than those of surrounding rock. The upper and the lower interfaces of the oil shale are strong wave impedance interfaces, which form a low-velocity wave-guiding layer with the oil shale as the center. This is conducive to the formation of seismic waves.
Q2: What are the similarities and differences between in-seam wave development in oil shale and coal seam?
A: The development of seismic wave depends on many factors, such as roof and floor lithology, coal seam thickness and its own physical characteristics. Comparing oil shale and coal seams, the physical properties are similar and can be collectively called oily coal seam, so seismic waves are also relatively developed.
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