Seismicity and the State of Stress in the Dezful Embayment, Zagros Fold and Thrust Belt

This study focuses on determining the orientation and constraining the magnitude of present-day stresses in the Dezful Embayment in Iran’s Zagros Fold and Thrust Belt. Two datasets are used: the first includes petrophysical data from 25 wells (3 to 4 km deep), and the second contains 108 earthquake focal mechanisms, mostly occurring in blind active basement faults (5 to 20 km deep). Formal stress inversion analysis of the focal mechanisms demonstrates that there is currently a compressional stress state ( in the basement. The seismologically determined SHmax direction is 37° ± 10°, nearly perpendicular to the strike of most faults in the region. However, borehole geomechanics analysis using rock strength and drilling evidence leads to the counterintuitive result that the shallow state of stress is a normal/strike-slip regime. These results are consistent with the low seismicity level in the sedimentary cover in the Dezful Embayment, and may be evidence of stress decoupling due to the existence of salt layers. The stress state situation in the field was used to identify the optimally oriented fault planes and the fault friction coefficient. This finding also aligns with the prediction Coulomb faulting theory in that the N-S strike-slip basement Kazerun Fault System has an unfavorable orientation for slip in a reverse fault regime with an average SW-NE SHmax orientation. These results are useful for determining the origin of seismic activity in the basin and better assessing fault-associated seismic hazards in the area.

Evaluation of hydrocarbon generation potential of source rock using two-dimensional modeling of sedimentary basin: a case study in North Dezful Embayment, Southwest Iran

Early Cretaceous and Jurassic sequences in the southwestern Iran host some of the largest hydrocarbon reservoirs in the globe. This study is aimed at evaluating the maturity of hydrocarbon fluids, migration paths, and characteristics of Pabdeh, Kazhdumi, Garu and Sargelu source rocks in this region. For this purpose, 27 samples of Pabdeh and Kazhdumi Formations from wells in the northern part of Dezful Embayment were chemically evaluated by Rock–Eval pyrolysis. OpenFlow™ software was utilized to analyze the burial history, conduct 1D thermal modeling in four oilfields and perform 2D modeling on a section to estimate the maturity and extension of sediments. Results of the 1D modeling showed that the kerogens of Sargelu, Garu and Kazhdumi Formations were properly matured, leading to some hydrocarbon outflow, although the organic matter content of Pabdeh Formation was too immature to produce any hydrocarbon. Based on the plot of hydrogen index (HI) versus Tmax, it was found that the studied formations were dominated by type II kerogen and a mixed species of type II and type III kerogens. Results of the migration path modeling showed some leakage from the Kazhdumi Formation up to an overlying seal that prevented the hydrocarbons from seeping out to surface. The Early and Middle Cretaceous oil systems were found to be connected through geometrical features or faults, with the Kazhdumi Formation separating the two systems. The results further showed the migration of hydrocarbons, at a relatively high rate, into the Abadan Plate through the sub-Kazhdumi reservoirs.The Early and Middle Cretaceous petroleum systems were found to be connected through particular geometry features or possibly faults, with the two systems separated by Kazhdumi Formation. For most part, the intensity of the maturation processes was found to decrease from east to west of the study area.

Implementation of an Integrated Geochemical Approach Using Polar and Nonpolar Components of Crude Oil for Reservoir-Continuity Assessment: Verification with Reservoir-Engineering Evidences

Summary The ability of geochemistry techniques in reservoir-continuity studies has already been proved. Most of the traditional methods mainly involve analyzing nonpolar components of crude oil and overlooking polar components. Despite valuable information obtained from nonpolar components, these compounds are sometimes affected by various alterations or likely provide only a piece of the reservoir-compartmentalization puzzle. In this paper, an integrated geochemical approach that uses nonpolar (i.e., saturates and aromatics) and polar (i.e., asphaltenes) components of crude oil was performed to evaluate reservoir continuity efficiently. The Shadegan Oil Field in the Dezful Embayment in southwest Iran was investigated for reservoir-continuity studies to show the efficiency of this proposed technique. The selected interparaffin peak ratios and light hydrocarbons [the C7 oil correlation star diagram (C7CSD)] from whole-oil gas chromatography (GC) (WOGC) chromatograms were used to obtain oil fingerprints from the nonpolar fraction of crude oils. The Fourier-transform infrared (FTIR) spectroscopy of asphaltenes was applied to obtain oil fingerprints from the polar fraction of crude oils. The pairwise comparison of studied wells by each technique was summarized in a similarity matrix with green, yellow, and red colors to show connectivity, limited connectivity, and disconnectivity according to oil fingerprints. Finally, a compartmentalization model was prepared from the integrated results of different techniques considering the worst-case scenarios regarding the occurrence or absence of reservoir continuity when relying on individual methods for the studied field. Results show that the Shadegan Oil Field comprises three zones in the Asmari Reservoir and two zones in the Bangestan Reservoir. Reservoir-engineering data, including pressure data and pressure/volume/temperature (PVT), completely corroborated the obtained results from the geochemical approach. The consistency of results suggested FTIR oil fingerprinting of asphaltene as a novel and straightforward technique, which is a complementary or even alternative method with respect to previous geochemical methods.