Thermal maturity of the Upper Triassic–Middle Jurassic Shemshak Group (Alborz Range, Northern Iran) based on organic petrography, geochemistry and basin modelling: implications for source rock evaluation and petroleum exploration

Abstract

Organic petrography and geochemical analyses have been carried out on shales, carbonaceous shales and coals of the Shemshak Group (Upper Triassic–Middle Jurassic) from 15 localities along the Alborz Range of Northern Iran. Thermal maturity of organic matter (OM) has been investigated using vitrinite reflectance, Rock-Eval pyrolysis and elemental analysis of kerogen. Reflectance of autochthonous vitrinite varies from 0.6 to 2.2% indicating thermally early-mature to over-mature OM in the Shemshak Group, in agreement with other maturity parameters used. The shales of the Shemshak Group are characterized by poor to high residual organic carbon contents (0.13 to 5.84%) and the presence of hydrogen-depleted OM, predominantly as a consequence of oxidation of OM at the time of deposition and the hydrogen loss during petroleum generation. According to light-reflected microscopy results, vitrinite/vitrinite-like macerals are dominant in the kerogen concentrates from the shaly facies. The coals and carbonaceous shales of the Shemshak Group show a wide range in organic carbon concentration (3.5 to 88.6%) and composition (inertinite- and vitrinite-rich types), and thereby different petroleum potentials. Thermal modelling results suggest that low to moderate palaeo-heat flow, ranging from 47 to 79 mW m−2 (57 mW m−2 on average), affected the Central-Eastern Alborz basin during Tertiary time, the time of maximum burial of the Shemshak Group. The maximum temperature that induced OM maturation of the Shemshak Group seems to be related to its deep burial rather than to a very strong heat flow related to an uppermost Triassic–Liassic rifting. The interval of petroleum generation in the most deeply buried part of the Shemshak Group (i.e. Tazareh section) corresponds to Middle Jurassic–Early Cretaceous times. Exhumation of the Alborz Range during Late Neogene time, especially along the axis of the Central-Eastern Alborz, where maximum vitrinite reflectance values are recorded, probably destroyed possible petroleum accumulations. However, on the northern flank of the Central-Eastern Alborz, preservation of petroleum accumulations may be expected. The northern part of the basin therefore seems the best target for petroleum exploration.

Geothermal Model of the Shallow Crustal Structure across the “Mountain Front Fault” in Western Lurestan, Zagros Thrust Belt, Iran

“…The diagram of Figure 7a shows how an increment of Q m (from 20 mW/m 2 to 25 mW/m 2 ) produces a shift of the Q S curve without changing its shape. Both curves remain within the range of 40-80 mW/m 2 , which is consistent with recent studies by Shekarifard et al [41] and by Kargaran and Neubauer [40]. The Q S curve obtained for a Q m value of 20 mW/m 2 provides a better fit as compared with the results by Kargaran and Neubauer [40].…”

“…The Q S curve obtained for Q m = 25 mW/m 2 shows a congruency in correspondence of vertical line 3, but displays a larger difference towards the NE. This comparison highlights how an analytical calculation (used in this work) produces different results with respect to published ones, however still in the range of Q S values of 40-80 mW/m 2 that are considered realistic for the Zagros thrust belt [40,41]. As a matter of fact, our temperature isolines are generally consistent with those obtained by Tunini et al [8] (Figure 7b).…”

Role of Composition and Depth on Pore Attributes of Barakar Formation Gas Shales of Ib Valley, India, Using a Combination of Low-Pressure Sorption and Image Analysis

“…The atomic H/C ratios of the samples are between 0.55 and 0.83, and the atomic O/C ratios are between 0.09 and 0.13. The H/C and O/C ratios of samples are plotted in the van Krevelen diagram, , which indicates type III kerogen (Figure ).…”

“…The atomic H/C ratios of the samples are between 0.55 and 0.83, and the atomic O/C ratios are between 0.09 and 0.13. The H/C and O/C ratios of samples are plotted in the van Krevelen diagram, 42,43 which indicates type III kerogen (Figure 3). The data indicate that the shale is a potent gas producer and derived from the alteration of terrestrial plant OM.…”

A complex based on imidazole ionic liquid and copolymer of acrylamide and phenoxyacetamide modification for clay stabilizer

“…It has been known that most of the formations faced in petroleum exploitation are shale formations . Clay minerals, as a major mineral of shale formations, may occur hydration, swelling and further migration when contacted with the external liquid, which is the main factor causing formation permeability damages and downhole accidents .…”