Correcting T_max Suppression: A Numerical Model for Removing Adsorbed Heavy Oil and Bitumen from Upper Ordovician Source Rocks, Arctic Canada

Abstract

A Rock-Eval 6 dataset of 66 samples from the Cape Phillips Formation in the Canadian Arctic region was studied to investigate source rock characteristics and petroleum generation potential. Bulk geochemical characteristics and thermal decomposition behavior of the samples indicate an initial generation potential close to 700 mg HC/g TOC and show an unusually low onset T max temperature for petroleum generation. This led to an examination of possible T max suppression due to a large amount of high-molecular-weight heavy oil and bitumen derived from the early breakdown of kerogen in the samples. Application of a numerical method based on kerogen decomposition kinetics allows for the numerical removal of thermal evaporative products of oil and bitumen adsorbed in the sample without requiring additional pyrolysis experiments or solvent extraction treatments of sample replicates. The removal of the adsorbed hydrocarbon from samples increases the T max value up to 17 °C. The estimated petroleum in the sorption phase varies from 1 to about 9 mg HC/g rock, depending on the total organic content (TOC) and maturity, and is the main form of the total oil yield in this area. The corrected T max–HI cross-plot suggests an onset of petroleum generation around 435 °C of T max, consistent with the general consensus for a normal marine source rock in this region. The constructed kinetic model shows a maximum of 75% transformation ratio (TR), and most samples show TR ranging from 10 to 50% in the early oil generation window on Cornwallis Island. This reconstructed source rock thermal decomposition model in a geological time scale indicates the onset of massive petroleum generation at a temperature of 120 °C, and the maximum transformation ratio of 75% corresponds to a temperature of 140 °C over geological time.

Thermal Maturity of the Grajcarek Unit (Pieniny Klippen Belt): Insights for the Burial History of a Major Tectonic Boundary of the Western Carpathians

“…This point is essential, because some factors suppress vitrinite reflectance and cause difficulties in determining the proper thermal maturity of organic matter. The suppression of vitrinite reflectance in coal or dispersed organic matter could be caused by (a) perhydrous vitrinite or vitrinite-like macerals due to the lipid incorporation (caused by variations in pH conditions or the chemistry of various plant components) derived from lignin, cellulose, or tannin (e.g., [85][86][87]), (b) the impregnation of bitumen or incorporation of migrated oil (e.g., [87][88][89]), (c) the abundance of liptinite macerals in a vitrinite poor-source rock (e.g., [90][91][92]) or (d) variable bacterial activity in sediments [93].…”

Thermal Maturation Regime Revisited in the Dongying Depression, Bohai Bay Basin, East China

“…Oil and gas generation stages are usually classified on the basis of %R o values even though the kinetics of kerogen thermal cracking differs from vitrinite particle rearrangement [6][7][8]. T max of the Rock-Eval pyrolysis offers the easiest way to assess source rock maturity levels [10]; however, T max suppression may occur in some liptinite enriched kerogens [11,12].…”