Method and system of determining elemental content of an earth formation

摘要

Determining elemental content of an earth formation. At least some of the illustrative embodiments are methods including: irradiating a portion of a formation that surrounds a borehole; counting gammas to obtain a spectrum of counted gammas; finding a solution to a system of equations based on the spectrum of counted gammas, which system of equations has a plurality of solutions, the solution being indicative of a plurality of weight percentages for a respective plurality of elements within the formation; determining whether the solution meets a predetermined constraint; repeating the finding and determining until a solution is found that is determined to meet the predetermined constraint; and producing an indication of the elemental content of the formation using the solution that meets the predetermined constraint.

主权项

1. A method comprising:
irradiating with neutrons a portion of a formation that surrounds a borehole with a source of neutrons from a tool positioned in the borehole; counting gammas of different energy levels in response to the irradiation to obtain a spectrum of counted gammas with a gamma detector positioned in the borehole; finding a solution to a system of equations based on the spectrum of counted gammas, which system of equations has a plurality of solutions, the solution being indicative of a plurality of weight percentages for a respective plurality of elements within the formation; determining whether the solution meets a predetermined constraint on the relative weight percentages indicated for at least two of the elements within the formulation; repeating the finding and determining until a solution is found that is determined to meet the predetermined constraint; and outputting an indication of the elemental content of the formation using the solution that meets the predetermined constraint.