Method for determining the extent of subsurface reaction involving acoustic signals
AssigneeDeutsche Texaco Aktiengesellschaft
InventorEike Rietsch
Life of this patent
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Abstract
A method determines the extent of subsurface reactions in which random acoustic signals are radiated from a whole area covered by the reaction or from a boundary region, hereafter termed reaction front, between largely undisturbed rocks and those already covered by the reaction. The signals are recorded by at least two receivers positioned at different locations outside the reaction area. The recorded signals are cross-correlated as a function of a time shift between the recorded signals so that at least one surface confining the reaction area is determined from the cross-correlation.
Claims8
A method for determining the extent of subsurface reactions in an earth formation in which random acoustic signals are radiated from that portion of the earth formation involved in the reaction comprising the steps of recording the acoustic signals by at least two receivers, and cross-correlating the recorded signals in accordance with one of the following equations:
- ##EQU2## where C.sub.AB is a cross-correlation function of a time shift .tau.,s.sub.A corresponds to the signal received by one receiver, s.sub.B corresponds to the signal received by the other receiver, and t is time so that at least one surface containing the reaction area is determined from the cross-correlation;
- and wherein two values of the time shift (.tau..sub.1, .tau..sub.2) are determined from the cross-correlation for which the values of the cross-correlation beginning with small shifts increases and, for the first time, exceeds the general noise level and, respectively, where the increased values of the cross-correlation finally return to the general noise level, and that from the absolute values of these time shifts (.tau..sub.1, .tau..sub.2) two vertex distances (d.sub.1, d.sub.2) are determined by multiplication of these shifts by the propagation velocity of acoustic signals, and that from these vertex distances (d.sub.1, d.sub.2) and the locations of the two receivers at focal points, two sheet hyperboloids of revolution are formed and the position of the reaction area is localized in such a way that, depending on the sign of the time shifts (.tau..sub.1, .tau..sub.2) the reaction area appears either inside or outside of one of the sheets of the hyperboloids of revolution.
Dependencies are inferred from the claim text.