نشریه زمین شناسی نفت ایران
سال ششم شماره 2 (پیاپی 612، پاییز و زمستان 1395)

Structural geological study is one of the most important stages of an oilfield exploration and production (E&P) program, since aknowledge of existing structures can play a fundamental role in the oilfield development plan. The main purpose of this study is to create threedimensional (3D) structural models to determine direction of tectonic stresses at Lali oilfield using subsurface geophysical data. The study area is located within the so-called Dezful Embayment (northern Khuzestan Province, Iran). Accordingly, in order to provide a 3D model of the reservoir, geostatistical tools in Petrel Software were utilized. Incorporating density log data into several coded formulations in MS Excel Software, the reservoir had its modulus of elasticity calculated. Subsequently, maximum and minimum horizontal stresses were calculated using poroelastic equations. Fault modeling results showed that, fault dip increases with increasing the depth towards the center of the field. Obtained values of stress using the poroelastic equations show that σ_H>σ_h>σ_v, confirming a regional reverse stress regime, which is consistent with previous studies in this area. Also, the formal stress ratios (Φ = (σ2-σ3) / (σ1-σ3)) obtained from poroelastic equations and inverse analysis method were found to be well-correlated across the area. Finally, average azimuth of the reverse faults on the southern limb (as calculated by Petrel) and the fractures on the limb (as obtained from FMI images and core samples) were found to be N305 and N315, respectively (average = N310). Thus, N040E was inferred to be the average direction of principal stress, i.e. principal stress is mostly directed along a NE-SW axis (perpendicular to the general trend of Zagros Orogeny); this is probably a result of the activities of youngest Zagros orogeny phase. The agreement between the obtained principal stress directions by fractures, faults, and focal mechanism of earthquakes across the World Stress Map (WSM) confirms the validity of this study.

In this research, biostratigraphy, microfacies, sedimentary environments and sequence stratigraphy (using by Cyclolog software) of the Asmari Formation are carried out. These studies are done on the basis of 580 samples (core and cutting) from 430 meters thickness of the formation from the well #2 of the Qaleh-Nar oilfield. Paleontological studies are led to identification of 23 genera and 28 species of the benthic and planktonic foraminifera. According to these microfossils, four assemblage zones have been recognized which confirm the age of Oligocene (Rupelian–Chattian) and Early Miocene (Aquitanian– Burdigalian) for the whole formation. Paleoenvironmental studies demonstrate 9 different microfacies that were deposited in the outer ramp (open marine) in the lower Asmari part, middle ramp (open marine to shoal) in the middle Asmari part and the inner ramp environment (tidal flat to lagoon) in the upper Asmari part. The sequence stratigraphy on the well #2 and the auxiliary well numbers 1, 3, 5, 6 and 7 of the Qaleh-Nar oilfield using by Cyclolog software reveals 7 positive breaks and 9 negative break levels alternatively. Some of the positive breaks define sequence boundaries and some of the negative breaks present the maximum flooding surfaces. In addition, a number of positive levels specify the major chronozone (stage boundaries). Comparison of the quintuple reservoir zones of the Asmari Formation in the Qaleh-Nar oilfield with the mentioned break levels suggests a fine correlation with these levels; however this correlation is invalid for other levels.

Electrofacies studies play an important role in the development process of a field. In these studies, poro-perm data of core analysis and well logs data can be used for reservoir simulation. In the present research, core analysis data (such as porosity and permeability) of selected drilled wells in Maroun oil field (SW Iran) divided into four flow units using regional fluid index method. Initial electrofacies (EF) model were determined using well logs data through different SOM, MRGC, and DYNAMIC. Determined facies of these methods were correlated with the flow units. The results indicated that SOM method is in the best concordance and so it was selected for classification of electrofacies. The initially nine electrofacies were reduced to 4 electrofacies type due to the similarity of some parameters such as effective porosity and shale volume. Reservoir quality was improved from EF-1 to EF-4. To valid the accuracy of the electrical rock type by neural networks, these electrofacies was correlated with capillary pressure data. Due to well correlation of determined electrofacies with capillary pressure data, the model was propagated to other wells of this field. This created model was able to separate different parts of the reservoir. In this model, different parts of the reservoir were determined in terms of reservoir quality. The model can be applied for providing of static model of the reservoir.

Asphaltene is always considered as a problem in oil industry. But, asphaltenes are desirable compounds in geochemical studies specially in oil-oil correlation. Oil-oil correlation is one of the most important issues in geochemical studies that enables to classify oils genetically. Asphaltenes due to their structural similarity with kerogen and unaffected and/or little affected from secondary processes are known as valuable compounds in geochemical studies. So, in this paper the structural characteristics of asphaltenes were considered as a correlation parameter. For this study 5 oil samples were collected from the Persian Gulf eastern part oil fields. Structural characteristics of these asphaltenes were investigated by Fourier transform infrared (FTIR) spectroscopy. 2D and 3D graphs based on aliphatic and aromatic compounds (predominant compounds in asphaltenes structure) and sulfoxide and carbonyl functional groups (which are representatives of sulfur and oxygen abundance in asphaltenes) were used for comparison of asphaltenes structures in different samples. According to the results of these defined graphs, the studied oil samples comprise two oil families with distinct genetic characteristics. The first oil family consists of the Salman and Reshadat oil samples, and the second oil family consists of the Resalat, Siri E and Siri D oil samples. To validation and complement the obtained results, the other common geochemical techniques such as stable carbon isotope and biomarkers parameters, were employed and these techniques completely confirmed previous results. According to biomarker parameters, the first oil family originated from marl source rock and the second oil family was sourced from carbonate source rock.

Mud volcanoes are geological structures formed as a result of gas emission, mud-fluid mixing and variably sized rock fragments in onshore and offshore settings. These structures are different morphologically which considered as significant marker of modern crustal movement and neotectonic activity. Occurrence of numerous mud volcanoes on the Makran accretionary prisms in Iran and Pakistan are reported which caused by the convergence of the Arabian and the Eurasian plates. In this study, origin of discharged hydrocarbon gases from three active onshore mud volcanoes; Ain, Borborok and Sand Mirsuban in Makran coasts of Iran were examined. The released gases of all these mud volcanoes are dominantly methane with concentration between 97.24-99.18 vol. % and minor amount of ethane (0.041.2 vol.%), propane (0.001-0.194 vol.%), n-butane (226 ppmvol.%), iso-butane (5-363 ppmvol.%), n-pentane (37ppmvol.%), iso-pentane (1-66 ppmvol.%), hexane (1-78 ppmvol.%) and CO2 (0.07-0.4 vol.%). Carbon and hydrogen isotope ratio of methane and its heavier derivatives indicate thermogenic source for emitted gases of all investigated mud volcanoes and evidences of the absence of biodegradation. CO2 with carbon isotope ratio of -11.1 to -14.3‰ is organic in origin. Our research suggests the presence of hydrocarbon system and active source rock in Makran active tectonic area. Although the occurrence of an exploitable gas reservoir in this area has to be confirmed by geophysical measurements, geological survey and structural settings.

This research concentrates on biostratigraphy, microfasies and sedimentary environment of the Asmari Formation at Davan village in 10 Km north of Kazerun. Micropalaeontological study led to recognition of 25 genera and 15 species of foraminifera. Based on biostratigraphic study 3 biozones (1-Nummulites vascus – Nummulites fichteli assemblage zone, 2 -Lepdocyclina-Operculina- Ditrupa Assemblage Zone, 3- Archaias asmaricus- Archaias hensoni- Miogypsinoides complanatus Assemblage Zone) are determined. As a result, the age of the Asmari Formation is Oligocene (Rupelian–Chattian) at the study area. Depositional texture, petrographic analyses and fauna led to identification of 9 carbonate microfacies related to open marine, slope, bar and lagoon. These depositional environments correspond to inner, middle, and outer ramp.