Detecting Heavy Bitumen Contaminations Using Corrected Rock-Eval Pyrolysis Data

Rock-Eval pyrolysis is a thermal method petroleum geologists use to evaluate source rock characteristics and obtain geochemistry parameters. However, there are misconceptions and misuses in exceptional cases that could lead to erroneous conclusions after using the Rock-Eval pyrolysis data to evaluate the properties of organic matter. However, a cross-plot of petroleum potential (S۲) versus total organic carbon (TOC) is a useful tool for solving issues and checking the accuracy of the geochemistry parameters. The graph provides the correction criteria for the S۲, hydrogen index (HI), and kerogen types. As well as the graph measures the adsorption of hydrocarbon by the mineral matrix. In addition, this article demonstrates a manner based on the data plot of S۲ versus TOC to detect bitumen or hydrocarbon contaminations. Based on our knowledge about the Garau formation as a possible source rock in the petroleum geology of Iran, a geochemistry study by Rock-Eval VI pyrolysis and LECO carbon analyzer has been conducted on many rock samples collected from different outcrops in the Lurestan province, Aligudarz region, from southwest of Iran, High Zagros. Plotting the data on a cross plot of S۲ versus TOC, drawing the regression line, and finding the regression equation are the best methods for determining the actual values of S۲ and HI parameters and bitumen/hydrocarbon contamination. Contamination creates a y-intercept in the graph of S۲ versus TOC, making geochemistry data unreliable in two study locations. The S۲ and HI data unrealistically increase, while the Tmax values decline and reduce the thermal maturity of the organic matter from its actual status. The y-intercept of the graphs is removed, and the corresponding values are subtracted from the HI and S۲ to skip the effect of contamination and obtain the actual geochemistry parameters. The cause of contamination in the Garau formation is the adhesion of heavy bitumen to organic facies due to the covalent bonds between carbon and hydrogen ions.

کلیدواژه ها:

Rock-Eval pyrolysis ، heavy bitumen contamination ، Geochemistry ، sedimentary system tracts