US 4,393,488 AGranted

Exploration system and method of determining elastic parameters and subsurface shape of an earth formation so as to indicate likelihood of the formation being an ore, marker rock, economic mineral or the like

AssigneeChevron Research Company

InventorsGary S. Gassaway, Henry J. Richgels, James I. Foster

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Abstract

The present invention provides for the accurate mapping of shallow crustal earth formations by means for refractive seismic waves to identify structure as well as elastic parameters of the strata undergoing survey to indicate deposits of ore, marker rock, economic minerals and the like. In one aspect of the present invention, a "roll-along" technique is used in the field, such technique being both practical and economical. In accordance with another aspect of the invention, there is a provision for (i) accurate separation and determination of seismic shear and compressional responses using three-dimensional hodographs; (ii) stacking displays that allow for accurate identification of shape of the surveyed strata; and (iii) final depth displays of the refracting bed segments associated with seismic shear and compressional wave velocities as well as Poisson's ratio to indicate presence of ore, marker rocks, economic minerals and the like.

Claims8

Dependent claims

Method of accurately determining shape and elastic parameters of an earth formation to identify ore, marker rocks, economic minerals or the like, using a refraction exploration field system including a series of detectors, positioned along a line or survey at inline positions X.sub.1, X.sub.2, . . . X.sub.n and at least one seismic source located adjacent to said detectors for producing a seismic wave for travel through said formation:

(a) generating a seismic wave at a first sourcepoint location adjacent said series of detectors;
(b) after said wave undergoes refraction, detecting arrival of a refracted wave at said series of detectors at said inline offset positions, to obtain a first set of traces associated with said offset positions X.sub.1, X.sub.2, . . . X.sub.n ;
(c) repeating steps (a) and (b) by generating a second wave at a second sourcepoint adjacent to inline position X.sub.n of said detector positions, and detecting said refracted wave to obtain a second set of traces;
(d) advancing said series of detectors a selected number of inline positions or fractions thereof and repeating steps (a), (b) and (c) above to obtain additional sets of traces, but in which said additional sets of traces are associated with more than two inline positions overlapping common inline positions of said first and second sets of traces;
(e) distinguishing arrival times of shear waves from compressional waves by means of a three-dimensional isometric hodograph generated by a computer-dominated process;
and
(f) depicting representations of arrival times of at least one segment of (i) shear waves and (ii) compressional waves as a function of inline position whereby shape of said earth formation as well as elastic parameters indicative of likelihood of said formation being an ore, marker rock, economic mineral, and the like, are provided.

4 more elements

Dependencies are inferred from the claim text.