A spreadsheet program to optimize kinetic parameters of organic matter from laboratory pyrolysis data
Transformation of sedimentary organic matter (OM) to hydrocarbons is best modeled by assuming the total reaction suite consists of parallel degradations of 'i' hypothetical components following the Arrhenius equation and first order kinetics. A kerogen can be defined by characterizing each constituent component by its activation energy (Ei) their initial potentials (Xios) and a single frequency factor (A). We present a user friendly Lotus 1-2-3 program to determine A, Ei and Xio distribution of OMs using a multiple linear regression utility and programmed macros. Rock Eval (RE) S-2 curves Of three heating rates are required. Equally spaced time/temperature and peak height data for S-2 curves of 'n' temperature steps in increasing order of heating rates are the inputs for the program. The fraction of hydrocarbon generated (f) from 19 hypothetical components of Ei 30, 32, 34...78 Kcal/mole for 'n' temperature/time steps, by using frequency factor (A) value and assuming Xios = 1, are calculated and set up in a 'n x 19' matrix (matrix M). The fraction of total hydrocarbon generated (f) at 'n' temperature steps, obtained from the observed peak heights, are set up in a 'n x 1' matrix (matrix L). Matrix M is suitably reduced by the program to 'n x k' matrix (matrix N) where 'k' is a variable, facilitating matrix inversion. Regressing matrix N against matrix L by the program, gives the Xios for 'k' Ei components along with a standard error (ERR) of Y estimates and R-2. Xios and A are then optimized iteratively by varying A values and selecting the solution associated with the lowest ERR value. Results of applying the program on data sets of two widely different types of samples from Indian basins are shown. They match the results obtained from the more sophisticated proprietary software. (C) 2000 Elsevier Science Ltd. All rights reserved.
arrhenius equation lotus 1-2-3 hydrocarbon generation rock-eval kerogen degradation