Method and apparatus for determining the thermal neutron capture cross-section of a subsurface formation from a borehole
AssigneeBaker Hughes Incorporated
InventorsW. Allen Gilchrist, Randolph J. Walser
Life of this patent
Estimating the term…
Abstract
Data acquired using a pulsed nuclear source are susceptible to two sources of error. One error is due to large statistical noise towards the end of an acquisition window. Another source of error is the contamination of the early portion of the data by borehole and other effects. The beginning of the processing window is adjusted based on the signal level at the end of the processing window for the preceding pulsing of the source. The end of the processing window is derived from statistical considerations.
Claims23
A method for estimating a parameter of interest of an earth formation with a tool having a nuclear radiation source and a nuclear radiation detector spaced apart from the nuclear radiation source, the method comprising:
- (a) activating the nuclear radiation source;
- (b) defining a starting time for a processing time window at which a measurement made by the nuclear radiation detector is responsive primarily to the parameter of interest and has a predetermined relationship to an estimated value of the parameter of interest at an ending time of a processing time window for an earlier operation of the source;
- (c) processing the measurements for determining a length of the processing time window at the end of which the measurements are substantially uncontaminated by noise;
- and
- (d) analyzing the measurements within the processing time window for estimating the parameter of interest.
(canceled)
An apparatus for use within a borehole penetrating an earth formation for estimating a parameter of interest of said earth formation, comprising:
- (a) a nuclear radiation source configured to irradiate the earth formation;
- (b) a nuclear radiation detector spaced apart from said nuclear radiation source;
- (c) a processor configured to:
- (i) define a starting time for a processing time window at which a measurement made by the nuclear radiation detector is responsive primarily to the parameter of interest and has a predetermined relation to an estimated value of the parameter of interest at an end of a processing time window for an earlier operation of the nuclear radiation source;
- and
- (ii) process the measurements to determine a length of the processing time window at the end of which the measurements made by the nuclear radiation detector are substantially uncontaminated by noise.
(canceled)
Dependencies are inferred from the claim text.