جستجوی مقالات مرتبط با کلیدواژه « organic facies » در نشریات گروه « زمین شناسی »

In this study, the organic facies and depositional environments of the Pabdeh Formation are investigated in the Rag-e-Sefid Oilfield located in the southern Dezful Embayment. Little information exists about the organic facies properties of this source rock in the Zagros basin. In the present study, a total of 4 cutting samples were collected from well No. 99 of the Rag-e-Sefid Oilfield. These samples are characterized by a combination of Rock-Eval pyrolysis and organic petrographic techniques. Based on the diagrams of Tmax versus HI, the studied samples contain type II/III kerogen with thermal maturity corresponding to the early stages of the oil generation window. Organic petrographic results are consistent with the presence of a highly organic-rich zone in the middle parts of the Pabdeh Formation, while the upper and lower parts are poor in organic matter. The organic-rich part of the Pabdeh Formation contains abundant amorphous organic matter, bituminite, and framboidal pyrite typical of anoxic depositional environment. The organic-poor sections on the other hand contain negligible organic matter with euhedral secondary pyrite in a light-colored matrix, which suggests oxic depositional condition. These observations suggest that different parts of the Pabdeh Formation were deposited under different environmental conditions. Only the middle part of the Pabdeh Formation has considerable potential for hydrocarbon generation.

In this research, the organic matter present in the Pabdeh Formation is investigated using Rock-Eval pyrolysis and organic petrographic techniques. For this purpose, a total of 22 cutting samples were collected at 50-meter intervals from 3 wells in the Kilur-Karim Oilfield. According to hydrogen index (HI) versus maximum temperature (Tmax) diagrams, the Pabdeh Formation in this oilfield contains type II/III kerogen, with thermal maturity corresponding to the early stages of hydrocarbon generation. In general, according to the Rock-Eval pyrolysis data, the middle parts of the Pabdeh Formation show a higher potential for hydrocarbon generation. On the other hand, organic petrography results show that samples from the middle parts of the Pabdeh Formation contain high amounts of amorphous organic matter along with solid bitumen. In addition, the upper and lower parts of this formation contain lower amounts of organic matter and mainly have abundant fossil content. A combination of results from two analytical techniques reveals that the Pabdeh Formation in the Kilur-Karim Oilfield contains a relatively organic-rich zone in the middle, which is surrounded by organic-poor facies above and below. These results can be helpful for a better understanding of the organic facies and palaeodepositional environments of the Pabdeh Formation in the study area.

Abstract The Dalichai Formation in the Ahvanu section, north of Damghan city, with a thickness of 78 meters, comprises alternations of bluish-gray marls and limestones. Microfacies and palynofacies studies, along with fossil evidence, including foraminifera diversity and abundance, the ratio of epifaunal to infaunal benthic foraminifera, and the ratio of surface to deep infaunal, were utilized to identify organic-rich layers and reconstruct trophic levels. These factors confirm a mesotrophic environment with average oxygen and nutrient levels for the Dalichai Formation (Bajocian to Lower Callovian) in the studied section. The primary reasons for low organic matter in the Dalichai Formation are attributed to low production and poor preservation of organic matter. However, dark-colored deposits with high organic matter at the Bajocian–Bathonian boundary and the lower and upper Callovian boundaries suggest increased production rates in anaerobic and eutrophic conditions. Macrofossil fragments (ammonites and echinoids) within limestone deposits at the uppermost part of the Dalichai Formation, exhibiting low organic matter, and the presence of Zeophycus trace fossils, suggest an oligotrophic environment with dysoxic conditions in the Upper Callovian.

The Upper Triassic Nayband Formation is widely exposed in the Tabas subzone, East Central Iran. This formation is 1410 meters thick, mainly comprises sandstone, sandy limestone, marl, coalificated shale (Coal seam) and dark shale in Parvadeh area. This study tries to reconstruct the hydrocarbon production potentiality, organic geochemistry, kerogen type, thermal maturity and recognition of depositional condition of the Nayband Formation. Totally 86 samples (coal seams and dark shales) were collected. These samples were analyzed by Rock-Eval type VI. Geochemical analysis results revealed that TOC content is more than 4 Wt% in the coalificated shales and in the dark shales is less than 4 Wt%. Parameters such as S1, S2, S1 S2 suggest poor hydrocarbon production. Other parameters such as HI suggest poor hydrocarbon production potential (coalificated shales) to gas prone source rock (dark shales). Results also revealed that the organic matter mainly contain type IV kerogen in the coalificated shales and predominately comprises kerogen types III and IV in the dark shales. Vitrinite reflectance of the coalificated shales (0.84-1.12 %) indicate that the coalificated shales are at the mature stage (enrichment of oxidized organic matter indicates poor hydrocarbon production). Organic facies of this rock unit indicates that these sediments predominately comprises organic facies types D and CD which implying highly oxic to oxic conditions during the deposition. Based on HI and TOC parameters, major of these sediments were deposited during relative sea-level fall.