f Rock-Matrix Adsorption Effect on Hydrocarbon Expulsion in Masjid-E-Solieman Oilfield, Sw Iran

The analysis of organic materials in sedimentary source rock is critical to interpreting their geology and petroleum-generation potential. The most readily available data on such organic materials are obtained by whole-rock Rock-Eval pyrolysis. For present study Masjid-e-Soleiman (MIS) oilfield in SW Iran, which is the first oilfield discovered in Middle East, was selected. Out of 314 producing wells drilled so far, 11 wells are drilled deep to the Sargelu Fm. at the depth of 15000 ft. Sargelu Fm. belongs to Middle Jurassic period with 200m thickness and comprises rich carbonaceous shales. Kerogen present in the studied Fm. as the major organic component is analyzed by Rock-Eval pyrolysis. Plotting the data on graph of S2 vs. Total Organic Carbon (TOC), and determining the regression equation is the best method for determining the true average hydrogen index and measuring the adsorption of hydrocarbon by the rock matrix. Such a plot also indicates the type of kerogen present and avoids the problem of increasing hydrogen index with total organic carbon content. With the S2 vs. TOC diagram, the organic component of different suites of samples may be compared and their petroleum generation potential established. Here the diagram is used to evaluate the sedimentary<br>environments and petroleum potential of the Jurassic carbonaceous shales of MIS oilfield in Zagros basin of Iran. The results reveal that comprised organic matter is of type III-IV mixed kerogen. This indicates oxidizing environment of deposition and explains the reason of high gas generation potential of the oilfield. The regression line in the S2 vs. TOC diagram which should pass the origin, has got either negative or very small intercept on the x-axis. This means that there is very low adsorption effect of rock matrix and this confirms and authenticates the carbonaceous nature of the studied shales. The amount of TOC was as high as 11.33 wt%. Major part of the organic content is inert due to terrestrial environment of deposition, at the same time high gas generation potential of this formation is due to its very high TOC content.