Locating Abandoned Mines Using the Active Mining Operation as the Seismic Energy Source – Demonstration of a New Method
This study demonstrates a new method for detecting the margin of old mine works using the seismic energy generated by active mining in the coal seam. As the first test of this new concept, the method should not be viewed as a proven, off-the-shelf technology, but rather a demonstration of the fundamental concept which has promise for detecting the margins of old mine works. For the primary method a linear spread of vertical 4.5Hz geophones on the earth’s surface was distributed across the margin of old mine works (both flooded and air-filled locations) and to a position over the active mining nearby. The seismic vibrations associated with the underground mining were passively recorded across this spread, with individual records as long as 32 seconds. Through a process of crosscorrelation, using each seismic trace sequentially as the pilot sweep for correlation with each other trace in the recording, two distinct seismic wave arrival patterns emerged from the data. The direct arrival from the mining operation to the surface through the rock overlying the coal seam was distinct and well represented in
Seismic‐while‐drilling by using dual sensors in drill strings
Drill-string waves can be successfully used as reference pilot signals for drill-bit seismic-while-drilling (SWD) purposes. The seismic signals obtained by correlating pilot and geophone measurements are disturbed by the drill-string reverberations because the pilot waves are reflected at each interface between string sections with different acoustic impedances. Inverse filtering of these reflections, using a reference-pilot deconvolution calculated in the presence of additional noise, may cause signal distortion. To overcome this problem, we consider using dual-sensor measurements in the drill string to remove the reflections of the drill-bit waves in the acquisition phase and to improve pilot deconvolution. We measure acceleration and strain of drill-string dual fields, which have opposite reflection coefficients and, in a string of constant elastic properties, the same transmission coefficients. These quantities are scaled to fit the amplitude of the direct arrivals, summed to remove the reflections in the drill string and in the rig, and may be deconvolved by Einstein deconvolution to characterize the reflection coefficient between the drill bit and the formation. Synthetic numerical examples and real measurements acquired downhole in a location close to the bit show that upgoing and downgoing drill-string pilots can be separated using dual fields and jointly used to improve the SWD seismograms.
Predicting the gas resource potential in reservoir C-sand interval of Lower Goru Formation, Middle Indus Basin, Pakistan
Abstract The integrated study of seismic attributes and inversion analysis can provide a better understanding for predicting the hydrocarbon-bearing zones even in extreme heterogeneous reservoirs. This study aims to delineate and characterize the gas saturated zone within the reservoir (Cretaceous C-sand) interval of Sawan gas field, Middle Indus Basin, Pakistan. The hydrocarbon bearing zone is well identified through the seismic attribute analysis along a sand channel. The sparse-spike inversion analysis has efficiently captured the variations in reservoir parameter (P-impedance) for gas prospect. Inversion results indicated that the relatively lower P-impedance values are encountered along the predicted sand channel. To further characterize the reservoir, geostatistical techniques comprising multiattribute regression and probabilistic neural network (PNN) analysis are applied to predict the effective porosity of reservoir. Comparatively, the PNN analysis predicted the targeted property more efficiently and applied its estimations on entire seismic volume. Furthermore, the geostatistical estimations of PNN analysis significantly predicted the gas-bearing zones and confirmed the sand channel as a major contributor of gas accumulation in the area. These estimates are in appropriate agreement with each other, and the workflow adopted here can be applied to various South Asian regions and in other parts of the world for improved characterization of gas reservoirs.