Hydrocarbon generation from lacustrine shales with retained oil during thermal maturation

Abstract

Thermal maturation in the shale oil/gas system is inherently complex due to the competitive interplays between hydrocarbon generation and retention processes. To study hydrocarbon generation characteristics from shales within different stages of thermal maturation under the influence of retained oil, we performed Micro-Scale Sealed Vessels (MSSV) pyrolysis on a set of artificially matured lacustrine shale samples from the Shahejie Formation in the Dongpu Depression in Bohai Bay Basin, China. Experimental results show that hydrocarbon yields of shale samples with or without retained oil at various thermal maturities follow different evolution paths. Heavy components (C 15+) in samples crack at high temperatures and generally follow a sequence, where they first transform into C 6-14 then to C 2-5 and C 1. Methane accounts for most of the gaseous products at high temperatures in all samples, with different origins. The cracking of C 2-5 is the main methane-generating process in samples with retained oil, whereas the source of methane in samples without retained oil is kerogen. In the studied shales, retained oils at early-mature stage retard the transformation of liquid to gaseous hydrocarbon and prompt the cracking of C 2-5 to C 1 to some extent. TSR reaction related to gypsum in the studied samples is the primary reason that can explain the loss of hydrocarbon yields, especially at high temperatures. In addition, transformation of volatile hydrocarbons to gas and coke also accounts for the loss of generated hydrocarbon, as a secondary factor.

A Study on the Applicability of Aromatic Parameters in the Maturity Evaluation of Lacustrine Source Rocks and Oils Based on Pyrolysis Simulation Experiments

“…Pyrolysis simulation experiments made it possible to study the hydrocarbon generation and hydrocarbon expulsion characteristics of the source rocks. They also provided an effective way to study, in depth, the evolutionary mechanisms of molecular markers. − By analyzing the experimental solid residues and hydrocarbon products, an immature-to-over-mature thermal evolution sequence could be established, and the evolutionary characteristics and validity of aromatic parameters could be studied. − Moreover, in comparing mixed source rock/oil samples in a certain area, as has occurred in some studies, the samples obtained from thermal simulation experiments were wholly the same type, making end-member analysis possible.…”

Study on the Applicability of Saturated Hydrocarbon Parameters in the Evaluation of Lacustrine Source Rocks and Oils Based on Thermal Simulation Experiments

“…Thermal simulation experiments not only make it possible to study the characteristics of hydrocarbon generation and expulsion of source rocks but also provide an effective way to study the applicability of biomarker parameters [26][27][28][29]. We can establish an immature to over-mature thermal evolution sequence by analyzing the experimental residues and hydrocarbon generation products at different temperature points.…”