Patent ID: 7520166

Claim:
A method for analyzing a hydrocarbon composition of homogeneous geological strata of a first drilling well through which a well drilling system extends, the drilling producing an effluent, the method comprising: determining, at successive depths, contents of a plurality of gaseous hydrocarbons in the effluent; establishing, at a substantially identical depth, a plurality of gaseous hydrocarbon content ratios, in pairs, for at least one first depth range, the establishing comprising plotting on a plot the content of a first of the gaseous hydrocarbons in the effluent at a given depth versus the content of a second of the gaseous hydrocarbons at the given depth for the successive depths in the at least one first depth range, each data point of the plot corresponding to one of the gaseous hydrocarbon content ratios; selecting, within the plot, from the plurality of gaseous hydrocarbon content ratios, a sub-group of reference ratios constituting a signature that is representative of a gaseous hydrocarbon composition of the effluent in the at least one first depth range, the signature being formed by at least one straight line which is taken from a group of straight lines, each of the straight lines having a given inclination value representing the content of the first gaseous hydrocarbon as a function of the content of the second gaseous hydrocarbon; and comparing the signature with at least one reference signature in order to determine the hydrocarbon composition of the geological strata corresponding to the at least one first depth range.