Patent Number: 052672743
Section: abstract

A method of analysis of rock samples taken from the bore of a well being drilled or from the Earth's surface and performed upon the apatite grains contained within the samples. The apatite grains are separated from the surrounding rock, polished to expose internal surfaces, and etched with acid to reveal the presence and characteristics of fission tracks within the apatite to determine the geological characteristics of the apatite. The grains containing the apatite are viewed under an optical microscope or other imaging apparatus and apatite crystals or crystal fragments which contain etched fission tracks are selected for analysis. If selected for analysis, measurements may be taken to determine the size and shape of the etched pits intersecting the apatite grain surface. The measurements are taken using a digitizing apparatus interconnected to a computer and containing a point light source superimposed upon the apatite grains viewed through the microscope. The measurements are used to determine the chemical composition of the apatite and in conjunction with data gathered by already existing methods, the fission track age and distribution of perceived track lengths for the fluorine-rich apatite grains are calculated. Determining chemical composition of apatite by this method eliminates procedures which are labor intensive, lengthy, costly, and potentially hazardous. The data derived from the analysis of the etched fission tracks are used as input criteria for existing kinetic modelling programs currently in use to constrain the temperature history of the apatite grains.