Methods and apparatus for constituent analysis of earth formations

A method for determining a characteristic of a system comprising a geological formation traversed by a well borehole, said method comprising the steps of:

• (a) determining at least one standard energy spectrum having a given resolution;
• (b) measuring by means including a detector in said borehole, an energy spectrum of radiation;
• (c) modifying said standard spectrum in a manner which reduces the effect of the difference between the detector resolution extant during said measuring step and the given resolution of said standard energy spectrum;
• and
• (d) comparing said measuring spectrum and the modified standard spectrum to determine a characteristic of the formation.

A method for investigating the composition of an earth formation traversed by a well bore through comparison of a measured spectrum of detected radiation, resulting from interactions between incident radiation and constituents of the formation, with a composite spectrum made of weighted standard spectra of constituents postulated to have contributed to said measured spectrum, comprising the steps of:

• (a) generating a filter operator and modifying said standard spectrum by said filter operator so as to provide a modified standard spectrum;
• (b) assembling a composite spectrum, one component of which comprises said modified standard spectrum;
• (c) deriving a difference indication corresponding to the fit discrepancy between the measured spectrum and the composite spectrum;
• (d) repeating said generating step, said assembling step, and said deriving step for a plurality of different filter operators to identify an optimum filter operator associated with a minimum difference indication.