Statistical analysis of relations between petrographic and geochemical indices of oil generation potential in organic matter

Abstract

To establish reliable indices for the synthetic assessment of petroleum potential using reworked sediment from mixed datasets, multivariate statistical analysis and cross-plots were used. New guidelines for improved assessment of generative potential and thermal maturity are suggested. Based on statistical analysis and cross-plots of HI, QI and BI versus the vitrinite reflectance (%Ro) and T max (°C), the HI max , QI max and BI max lines are defined between the vertex of the upper and lower limits of the HI-band, QIband and BI-band as defined by a majority of the samples. The constructed HI, QI and BI bands were broad at low maturities and gradually narrowed with increasing thermal maturity. The petroleum generation potential is completely exhausted at a vitrinite reflectance of 2.0-2.2% or a T max of 510-520°C. An increase in HI and QI suggests extra petroleum potential related to changes in the structure of the organic material. A decline in BI signifies the start of the oil expulsion window and occurs within the vitrinite reflectance range 0.75-1.05% or a T max of 440-455°C. Furthermore, petroleum potential can be divided into four different parts based on the cross-plot of HI versus %Ro. The area with the highest petroleum potential is located in section II with %Ro = 0.6-1.0%, and HI [ 100. Oil generation potential is rapidly exhausted at section III with %Ro [ 1.0%. This result is in accordance with the regression curve of HI and QI with %Ro based on 80 samples with %Ro = 1.02-3.43%. The exponential equation of regression can thus be achieved: curve, HI = 994.81e -1.69Ro (R 2 = 0.72) and QI = 1646.2e -2.003Ro (R 2 = 0.72). The worldwide organic material dataset defines two oil expulsion windows represented by the upper and lower limits of the BI band: %Ro * 0.75 to *1.95% or T max * 440 to *525°C, and %Ro * 1.05 to *1.25% or T max * 455 to *465°C, respectively. The start of the oil expulsion window occurs within the %Ro range of *0.75-1.05 %Ro or the T max range *440-455°C and the total oil window extends to %Ro = * 1.25-1.95 or T max = * 465-525°C.

Correlation among Vitrinite Reflectance Ro%, Pyrolysis Parameters, and Atomic H/C Ratio: Implications for Evaluating Petroleum Potential of Coal and Carbonaceous Materials

“…Obtaining geochemical data by heating a small amount of rock powder through pyrolysis process is an important geochemical tool in oil exploration. Nevertheless, the rock itself contains inorganic mineral matrices and the oil pollutants generated in the sampling process will reduce the hydrogen index (HI) value (Udo et al, 1986;Dahl et al, 2004) and affect the assessment for kerogen type and quality (Akinlua et al, 2005;Lee, 2010;Lee, 2011). As a result, when assessing the hydrocarbon potential of kerogens, one should not rely solely on the Rock-Eval pyrolysis parameters from pyrolysis analysis but also graph the atomic H/C ratio, TOC, and Ro% against one another to confirm and double check the results for accurate assessment.…”