Source Rock Maturation Modeling as an Exploration and Evaluation Tool: An Example From the Southern Part of the Zagros Fold Belt in Iraq

摘要

Geochemical analyses of several hundreds of samples taken from few tens of deep wells and surface sections in the Zagros simply folded belt in north east Iraq show that there are two main source rocks in the studied area. The middle-upper Jurassic source rocks with an average TOC=1.5% consist of Kerogene type IIS, and the upper Triassic ones with TOC=0.5% consist of Kerogene type III. The maturation of the middle-upper Jurassic source rocks was modelled using their measured physical parameters and basing on the analysis of the Phanerozic tectonic history of the north eastern margin of the Arabian plate ( The Zagros fore deep in northern Iraq). The burial and thermal histories of the sampled locations and many hypothetical locations randomly distributed along the studied area were also reconstructed. The results of the modeled maturation levels of these source rocks show a very good positive correlation with the measured maturation levels of the same source rocks at the locations of sampling (correlation coefficient=+0.90). These positive relations postulated that the modeling procedure and the modeling parameters were considerably correct, and the results of the models are applicable in the whole basin. Detailed structure study was also carried on and several structure and paleogeographic maps and cross sections were also constructed. The possible hydrocarbon migration routes were defined and correlated with the discovered present traps. The predominance of natural gas reservoirs in the southern parts of the Zagros fore deep in Iraq versus the predominance the oil reservoirs in the northern parts of it, is also in very good correlation with the results of both the burial and thermal histories model and the reconstruction of the structural evolution of the studied area. The results of the correlations between the predicted locations of the hydrocarbon trapping and the locations of the discovered actual traps were also very good. But the calculated amounts of the possibly produced hydrocarbons, since the time of the evolution of the present structures of the studied area, are more than three times than the actual present discovered volumes of the hydrocarbons.