Patent Document ID: 4841490
Application ID: 07208183
Patent Flag: 1

Claim One:
1. A method of identifying underground geological strata from a plurality of seismic traces Sk(t) recorded in a borehole at different levels k of depth Zk, wherein each trace Sk(t) includes n discrete sample values sampled as a function of time t at a constant time interval .DELTA.t, the method determining the series R={r.sub.i, for i=1,n} representative of seismic reflection coefficients at the interfaces formed between successive geological strata, wherein i is an index relating to the sampling depth on a time scale at the constant interval .DELTA.t, said method including the steps of: establishing the time-depth curve relating the depth Zk to the transit time Tk recorded on the trace Sk(t) for each level k; extracting the upgoing wavefield Uk(t) and the downgoing wavefield Dk(t) from the traces Sk(t); and calculating U.sup.mean (t), U.sup.min (t), and U.sup.max (t) representative of mean value, minimum value, and maximum value, respectively, of the upgoing wavefield Uk(t-Tk), and calculating D.sup.mean (t), representative of mean value of the downgoing wavefield Dk(t+Tk); said method further including the steps of: (a) determining a series R.sup.o ={r.sup.o.sub.i }, representative of an approximation to the series R, by minimizing the function EQU H(R)=.SIGMA.f(r.sub.i) wherein f(r.sub.i) is an increasing function of .vertline.r.sub.i .vertline., which is symmetrical on the X axis, concave, and satisfies the constraint EQU R*D.sup.mean (t)=U.sup.mean (t) wherein the operator * represents a convolution product; (b) determining a series .DELTA.R={.delta.r.sub.i } representative of a value for correcting the series R.sup.o, and minimizing a function J(.DELTA.R) which is linear in .vertline..delta.r.sub.i .vertline. under the constraints: EQU U.sup.min (t)&lt;[(R.sup.o +.DELTA.R)*D.sup.mean (t)]&lt;U.sup.max (t) and EQU .vertline.Zk-Zks(R.sup.o +.DELTA.R).vertline.&lt;.epsilon.k wherein Zks(R.sup.o +.DELTA.R) is a linearized function in .DELTA.R representative of the depth Zks calculated synthetically at level k from the initial solution R.sup.o and the magnitude .epsilon.k is representative of the uncertainty in the magnitudes of Zk and Tk; and (c) calculating the series R=R.sup.o +.DELTA.R{R.sub.i =r.sup.o.sub.i +.delta.r.sub.i } representative of seismic reflection coefficients.