Patent ID: 6091669
Filing Date: 2000-07-18
Classification: G01V

Abstract:
A method for determining, displaying and utilizing the relative changes of elastic moduli and that of density of geologic formations, said relative changes of elastic moduli being the relative change of Lame constant .DELTA..lambda.(.lambda.+2 .mu.), the relative changes of shear modulus .DELTA..mu.(.lambda.+2 .mu.) and/or .DELTA..mu./[.kappa.+(4/3).mu.], the relative changes of bulk modulus .DELTA..kappa./[.kappa.+(4/3).mu.], and said relative change of density being .DELTA..rho./.rho., comprising the steps of:(a) collecting multiple coverage common-mid-point or common-depth-point seismic data using propriety surface detector- and shot-point spreads, the maximum of the incidence angles of seismic waves impinging at the reflection boundary of geologic formations of exploration target being within 30.degree..about.45.degree. and being smaller than critical angle in case critical reflection occurring;(b) Pre-processing the seismic data to obtain the post-processed and corrected common-reflection-point gathers so that the amplitude-versus-incidence-angle-variation of which at the same reflection time represents the reflection-coefficient-versus-incidence-angle-variation;(c) estimating incidence angles of the same sampling time, i.e. the incidence angles from the same reflection point but with different offsets;(d) fitting the reflection amplitudes and corresponding incidence angles of the same reflection point with a variety of offsets into the first approximate linear relations:R(.theta.).tbd.A(1+sin.sup.2 .theta.+sin.sup.2 .theta.tg .sup.2 .theta.)/4+B(1-3sin.sup.2 .theta.+sin .sup.2 .theta.tg.sup.2 .theta.)/2 +C(1-sin.sup.2 .theta.-sin.sup.2 .theta.tg.sup.2 .theta.)/4and/or the second approximate linear relationsR(.theta.).ident.D(1+sin.sup.2 .theta.+sin.sup.2 .theta.tg.sup.2 .theta.)/4+E(1-5sin.sup.2 .theta.+sin.sup.2 .theta.tg.sup.2 .theta.)/3 +C(1-sin.sup.2 .theta.-sin.sup.2 .theta.tg.sup.2 .theta.)/4which results in two over-determined linear equation groups; where A=.DELTA..lambda./(.lambda.+2 .mu.), B=.DELTA..mu./(.lambda.+2 .mu.), C=.DELTA..rho./.rho., D=.DELTA..kappa./[.kappa.+(4/3).mu.], and E=.DELTA..mu./[.kappa.+(4/3).mu.];(e) solving the said over-determined linear equation groups to determine coefficient A, B, C and/or D, E, C;(f) repeating steps (c), (d) and (e) for each sampling time of a common-reflection-point gather,(g) repeating steps (c), (d), (e) and (f) for each common-reflection-point gather of a line,(h) displaying said coefficients determined above of each over-determined linear equation group by three plotting methods of which are the single relative change profile, the comprehensive direct hydrocarbon detection profile and the crossplot; for the single relative change profile plotting method, one relative change, i.e. one coefficient, is plotted in one figure; for the comprehensive direct hydrocarbon detection profile plotting method, the three coefficients of one over-determined linear equation group being specially combined into one figure, according to their signs of value (i.e. positive or negative) or according to that they are bigger or smaller than their thresholds, being represented by different colors or symbols; for the plotting method of 2-dimensional crossplot, one coefficient from the three coefficients of one over-determined linear equation group being selected as reference variable while the other two coefficients as the abscissa and ordinate variable respectively, and different symbols or colors being used for representing positive or negative of the reference variable; for the plotting method of 3-dimensional crossplot, the three coefficients of one over-determined linear equation group being selected as X-, Y- and Z-variable, respectively.