نشریه زمین شناسی نفت ایران
سال نهم شماره 2 (پیاپی 18، پاییز و زمستان 1398)

Reconstruction of the sedimentary environment of the Middle-Upper Maastrichtian deposits (Tarbur Formation) in the Murak area (southwest of Semirom) was performed based on Microfacies and microtaphofacies analysis. The formation with 239 m thickness consists of limestone and shale. Meanwhile, the Tarbur deposits overlie the Gurpi Formation and is covered by the Paleocene deposits. Seven and five microfacies and microtaphofacies were recognized based on the main components and sedimentological and taphonomical features, respectively. In addition, these microfacies and microtaphofacies were deposited in homonicnal carbonate ramp. From the viewpoint of vertical distribution and interpretation of microfacies and microtaphofacies, the Tarbur deposits were formed in the energetic environment (under the influence of the storm waves) in the study area. Therefore, communities of rudist are absent and the green algae (Dasycladales) are abundant in the study area. Concerning the high rate of detrital grain input and increasing of nutrients, the bryozoans were performed the encrusting more than other organisms.

Drilling mud loss is considered as one of common problems encountered during excavation. The aim of this study is to evaluate of mud loss of the Sarvak Formation (Cenomanian age) in Azadegan oil field which is known as the most important rich hydrocarbon reservoir in the Zagros region by providing the model in the environment of GS+ software. This formation consists of a thick sequence of limestone and clay limestone layers, which is divided into 7 zones based on petrophysical characteristics. For this purpose, available data such as drilling mud weight, pump pressure, mud loss, and related depths of 9 drilled wells were investigated. The results showed that despite of the operating factors including the weight of drilling mud and the pressure of the pumps were kept constant, the presence of fractures in the reservoir rocks causes to occur mud loss significantly in zone 3 while it is observed the lowest level of mud loss in zone7. Based on the results of mud lost data patterns, faults, sedimentary environments morphology (such as sedimentary channels) seem to play major roles in creating fractures or areas susceptible to mud loss. The difference in observed patterns of mud loss is more likely to confirm the relocation of channel status over the time in different parts of the reservoir. In general, the highest rate of mud loss was detected in the northern and southern edges while the lowest rate was happened in the middle part of the field. It is suggested to prevent mud loss hazards in this field, underbalanced drilling method should be used.

One of the most common and relatively accurate methods for determining the amount of organic carbon in rocks in the oil and gas exploration potential is the Pyrolysis family, a standard example of which is the first rock pyrolysis method. Based on the study of the core, this method explores the potential of oil and gas resources in rocks. One of the important and valuable parameters in determining the potential of oil and gas resources is the determination of TOC. The purpose and motivation of this research is to compare the ΔlogR method and the mineralogy-based method for calculating the total amount of organic carbon in the source rock. It has the desired accuracy and relatively low cost. The fields studied in this study are two fields of Ahwaz and Rag-e sefid. These fields are among the potential fields of southwestern Iran for more detailed investigation and estimation of organic carbon content. In this research, software studies have been performed through IP software, using which the petrophysical data of each field have been calculated and compared, and finally, its results have been compared with actual TOC values. Input data in the mineralogical data method include density log, neutron porosity log and gamma log, and input data in the ΔlogR method include acoustic and resistivity logs. According to the fields, the most appropriate methods (in terms of R2) in Ahwaz and rag-e sefid fields are the mineralogical data method and the ΔlogR method, respectively. Also, in terms of cost, precision and accuracy parameters, the best method discussed in this research is R2 mineralogical data in Ahwaz and Rag-e sefid, 0.94 and 0.61, respectively. After this, the ΔlogR method comes second.

In this study, Abderaz Formation at Qalezo section in the west of the Kopeh-Dagh sedimentary basin has been studied. It has consisted mainly of massive limestone, Marl and chalky limestone units at the mentioned section. Abderaz Formation at Qalezo section, the lower contact with Aitamir Formation is paraconform and the upper contact with Abtalkh Formation is conformed and continuous. The thickness of Abderaz Formation, 216 meters, has been measured. In this investigation have been identified 55 planktonic foraminifera species belong to 15 genera, in a frame of 4 biozones have been recognized. Finally, based on this research was distinguished from latest Early Turonian-Late Santonian ages for this section. In this study four planktonic foraminifera species, Dicarinella bouldinensis (Pessagno 1967), Dicarinella takayanagii Hasegawa 1999, Marginotruncana desioi (Gandolfi 1955), Marginotruncana caronae Peryt 1980 have been introduced for the first time in Iran. Also in this research planktonic foraminifera test geometric in Abderaz Formation at Qalezo section has been studied for sea-level changes. In Lower-Middle Turonian substages, the high frequency of the M1 group and low frequency of M3 group displayed fall seal level at this time. In Late Turonian frequencies of M3 group with accompany of %P was shown rise sea level. In the Coniacian and Santonian stages, the M1 group is dominant and the M3 group is low frequency and all of the mentioned evidence were demonstrates fall sea level. Also, the depth average of the studied section based on Depth = e (3.58718 + (0.03534 × %P)) has been calculating 146 meters which were shown these sediments deposited in Outer Neritic environment.

Study of Late Devonian-Carboniferous (Mississippian-Pennsylvanian) conodonts Anarak section (NE Isfahan), Central Iran, led to identifying 67 conodont species belonging to 18 genera. 22 conodont bio-intervals were separated; 15 biozones belong to Late Devonian and 7 biozones belong to carboniferous (Mississippian-Pennsylvanian) time interval. Based on field observation and sedimentological featurs and charactristics the section, subdivided into 5 lithostratigrafic unit. The Color Alteration Index (CAI) reveals the hydrocarbure potential for the Famennian stage of the studied interval

The Sand tongues of the Albian Kazhdumi Formation is a major prodactive reservoir in North West part of the Persian Gulf towards Kuwait . High porosity and high permeability of these sandstones together with existence of shale either as source rock or cap rock in this formation, have provided all conditions needed for hydrocarbon accumulation. A rapid sea level fall in ealry Albian initiated the deposition of Burgan clastic reservoirs over the Shuaiba Carbonates. The lower Burgan Formation was deposited in a lowstand systems tract represented by massive sandstone reservoirs. High frequency sealevel changes have resulted in deposition of shoreface sands and extensive marine shales within an overall fluvial setting. The middle part Burgan was deposited in a transgressive systems tract. The upper part witnessed a relative sealevel fall in a lowstand systems tract with deposition of sand prone facies in estuarine channels. The clastic cycle was terminated by initiation of Mauddud carbonate sedimentations in transgressive systems tract. A combined effect of allocyclic nesting of sequence stratigraphic packages and autocyclic ramp profile were the primary factors controlling the lithofacies association. This Formation has been informally subdivided into:Lower Interval (C) mainly shaly sands, middle Interval (B) clean sands “main reservoir” and upper Interval (A) interbedded shale & sands. Petrographic analysis shows that the reservoir consists of quartz-rich sands, (typically>70%) and feldspar poor (mainly <5%). Nine authigenetic minerals in the Burgan sands have been identified: quartz, calcite, siderite, pyrite, glauconite along with four groups of the clay minerals. XRD analysis of clay fraction indicates the presence of four clay mineral groups in the Burgan reservoirs : kaolin, illite , chlorite and expandible- lattice mixed –layer, illite/ smectite.