Petroleum Engineering
Meisam Hemmati; Yaser Ahmadi
Abstract
The Rock-Eval pyrolysis is a thermal method that is widely used by the petroleum geologist for evaluation of 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 ...
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The Rock-Eval pyrolysis is a thermal method that is widely used by the petroleum geologist for evaluation of 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 S2 (petroleum potential) versus TOC (total organic carbon) is the usable tool to solve issues and applied for checking the accuracy of the geochemistry parameters. The graph provides the correction criteria for the S2, HI (hydrogen index), and kerogen type. 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 S2 versus TOC to detect bitumen or hydrocarbon contaminations. Based on our knowledge about the Garau Formation as a possible source rock in 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 South-West of Iran, High Zagros. Plotting the data on a cross plot of S2 versus TOC, drawing the regression line, and finding the regression equation are the best method for determining the real values of S2 and HI parameters and bitumen/hydrocarbon contamination. Contamination creates a y-intercept in the graph of S2 versus TOC which makes geochemistry data unreliable in two study location. As, led to the S2 and HI data unrealistically increased, while the Tmax values went down and reduced the thermal maturity of the organic matters from its real status. For skipping the effect of contamination and obtaining the real geochemistry parameters, the y-intercept of the graphs removed and the corresponding values subtracted from the HI and S2. 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
Petroleum Engineering
Meisam Hemmati; Yaser Ahmadi
Abstract
Knowing the characteristics of suitable environments for precipitation of oil prone source rocks facilitates oil explorations and leads to development of oil fields. The current study investigates the organic matter properties and sedimentary environment conditions of the Garau Formation in various outcrop ...
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Knowing the characteristics of suitable environments for precipitation of oil prone source rocks facilitates oil explorations and leads to development of oil fields. The current study investigates the organic matter properties and sedimentary environment conditions of the Garau Formation in various outcrop sections in Lurestan province from south-west of Iran (High Zagros) with using elemental analysis, visual kerogen analysis and Rock-Eval pyrolysis data. The geochemistry parameters indicate that the Garau Formation is an excellent oil prone source rock and composed of kerogen type I and II. The oxygen index (OI) is very low which reveals that organic matter deposited in an anoxic sedimentary environment and suitable for the preservation of organic matter and hydrocarbon generation. The visual analysis of isolated kerogens from source rock samples indicates the abundance of dark amorphous organic matter (AOM) with small amounts of phytoclasts and pyrite with no palynomorphs. Sedimentation seems to have occurred in deep and reduced parts of a carbonate basin during a rapid transgression. In addition, due to the effect of thermal maturation, the color of amorphous organic matter has darkened. The elemental analysis and Van-Krevelen diagram was shown that the type of organic matter and reveals the thermal maturity of the oil window. Moreover, amount of pyritic sulfur (Sp) and organic sulfur (So) contents have been calculated, and it was reveals that the high content of organic sulfur is a key element in the structure of organic matter.