Geological Environment and Engineering
Shirin Samani; Ali Uromeihy; Amirhossein Enayati; Imandokht Mostafavi; Misha Pezeshki
Abstract
Diagenetic processes in carbonate rocks can be considered as one of the most important factors influencing the inherent characteristics of this type of reservoir on a small as well as large scale. Considering the importance of knowing the mechanical characteristics of reservoir rocks in geomechanical ...
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Diagenetic processes in carbonate rocks can be considered as one of the most important factors influencing the inherent characteristics of this type of reservoir on a small as well as large scale. Considering the importance of knowing the mechanical characteristics of reservoir rocks in geomechanical modeling and its application in the exploitation and development of hydrocarbon fields, it is necessary to find out how lithological characteristics affect its rock mechanical behavior. In this study, the impact of two diagenetic processes (Dolomitization and Anhydrite cement) on the physical and mechanical characteristics (such as Uniaxial Compressive Strength, Young’s modulus, Cohesion, and Internal friction angle) of carbonate reservoirs of the Kangan Formation, are addressed. The evaluations have been done in two phases: i.e., lithological studies and rock mechanical tests. The results show that changes in mechanical properties are strongly influenced by diagenetic processes. The two main influential features on mechanical characteristics are dolomitization and anhydrite cementation, which strongly affect porosity, dominant pore type, and mineralogy. The results show that dolomitization in the studied samples has caused an increase in porosity and a decrease in strength and elasticity. While the presence of anhydrite has caused an improvement in the resistance characteristics with an opposite effect.
Sedimentology
Umid Kakemem; Mohammad Adabi; Ehsan Dehyadegari
Abstract
Depositional texture, sedimentary structure and present fauna led to characterize twelve carbonate- evaporate facies. These facies were classified in three facies belts including tidal flat, lagoon and shoal. Developpment of tidal zones together with evaporate deposits and thrombolite facies (signs to ...
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Depositional texture, sedimentary structure and present fauna led to characterize twelve carbonate- evaporate facies. These facies were classified in three facies belts including tidal flat, lagoon and shoal. Developpment of tidal zones together with evaporate deposits and thrombolite facies (signs to a shallow depositional environment), the absence of continuous reef‐frame builders, high production of carbonate mud, absents of calciturbidite, tempestites deposits and slump structures are evidences for a homoclinal carbonate ramp setting. The facies based on petrophysical characteristics which is the results of depositional texture and diagenesis are classified in seven reservoir rock types. In which, the first rock type (RT1) has weak reservoir property and toward RT7 reservoir quality will increase. Facies variation related to sea level fluctuations led to subdivide the whole strata into two 3rd order sequences. Facies stacking patterns in the sequences characterized by subtidal facies (lagoon and shoal) tend to have the most reservoir quality that covered by evaporative (Mf1) and peritidal facies (Mf2 to Mf4) with low-reservoir quality. The most reservoir quality in both K1 and K2 reservoir zones is coincident with late TST, maximum flooding surface (mfs) and late HST in identified depositional sequences which is settled in high-energy shoal facies intervals.
H Vafaei; M Peyravi
Abstract
The Kish gas-field is one of the world’s largest gas-fields, and consists of two reservoir rocks of Kangan (Lower Triassic) and Dalan (Late Permian) formations in the Zagros sedimentary basin. In this study, the Kangan formation has been examined. In this research, in addition to the use of raw ...
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The Kish gas-field is one of the world’s largest gas-fields, and consists of two reservoir rocks of Kangan (Lower Triassic) and Dalan (Late Permian) formations in the Zagros sedimentary basin. In this study, the Kangan formation has been examined. In this research, in addition to the use of raw data obtained from logging of a drilled well from the whole extent of the field, probabilistic petrophysics evaluation method was used to assess the petrophysical properties (shale volume, lithology, porosity and water saturation) of the Kangan formation. A method based on statistics and possibilities was also utilized to interpret the graphs (logs) with the help of multi-mineral model, a module of Multimin Software. Based on the results of this assessment and the use of lithology-determining cross-plots, as well as standard charts of Schlumberger, the dominant lithology of the Kangan formation in the studied well was recognized as calcite, dolomite, some anhydrite and small amounts of shale. The ultimate aim of the petrophysical evaluation in hydrocarbon studies of the Kish gas-field is to provide proper inputs to the reservoir static model. In order to make a more detailed study, this formation was divided into two parts, K1 and K2. As a whole, the calculated volume shale in the Kangan formation in this well is low and in K2 part is less. This could be considered as a reason for the equal effective porosity in most of the points along the well.
A. Kamkar Rouhani; M. Zakeri
Abstract
In order to obtain more accurate results from application of the method of artificial neural networks, instead of selection of the best network determined by trial and error process, we suitably combine the results of several networks that is called committee machine, to reduce the error, and thus, increasing ...
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In order to obtain more accurate results from application of the method of artificial neural networks, instead of selection of the best network determined by trial and error process, we suitably combine the results of several networks that is called committee machine, to reduce the error, and thus, increasing the accuracy of the output results. In this research, ensemble combination of single artificial neural networks has been used in order to estimate the effective porosity of Kangan gas reservoir rock in South Pars hydrocarbon field. To achieve this goal, well logging data of 4 wells in the area at the depth interval corresponding to Kangan formation were used. Acoustic, density, gamma ray and neutron porosity well log data were assigned as the input of the networks while the effective porosity data were considered as the output of the networks. Back- propagation single neural networks having different structures were trained using regularization method and their results were assessed. Then, the networks with the best results, i.e. contained minimum mean of squares of errors in the test step, were selected for making ensemble combinations. To determine the weighting coefficients of the networks in the linear ensemble combinations, we applied three methods of simple averaging, Hashem’s optimal linear combination and non-analytical optimal linear combination employing genetic algorithm, and their results were compared. The best ensemble combination, in which we had the maximum reduction in mean of squares of errors of the test step compared to the best single neural network, was an optimal linear four-network combination obtained by using genetic algorithm optimization method. This best ensemble combination, compared to the best single neural network, reduced the mean of squares of errors in the training and test steps 3.6% and 11.2%, respectively.
A. Rajabi-Harsini; M. Memariani
Abstract
In this study, in order to evaluate the geochemical characterization of Kangan Formation in well B in South Pars Gas Field, geochemical analysis (including preliminary and complementary analysis such as Rock-Eval Pyrolysis, extraction of organic matter (EOM), bitumen fractionation, Gas chromatography ...
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In this study, in order to evaluate the geochemical characterization of Kangan Formation in well B in South Pars Gas Field, geochemical analysis (including preliminary and complementary analysis such as Rock-Eval Pyrolysis, extraction of organic matter (EOM), bitumen fractionation, Gas chromatography and Gas chromatography-Mass Spectrometry) were carried out on core samples. Geochemical results reveal that these samples have kerogen type III and II, indicating a marine organic matter with a little terrestrial input. The organic matter of these samples was derived from source rock(s), with clastic-carbonate lithology which deposited under anoxic to subanoxic conditions. In addition, the above samples exhibt poor to moderate genetic potential with kerogen maturity at the beginning of oil generation (late diagenesis to early catagsnesis). Also, based on column chromatography, the above samples are mainly composed of paraffinic-naphthenic and paraffinic hydrocarbons. A negligible amount of hydrocarbons seems to have been generated locally from Kangan Formation.
A. Rajabi-Harsini
Abstract
Silurian shales (Sarchahan Formation), with high volume of organic matter, are the major source rock of Dehram Group reservoir in South Pars Gas Field. Residual oil (bitumen) were seen on some parts of Kangan Formation core. According to some reports, Lower Triassic (Kangan Formation) sediments is a ...
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Silurian shales (Sarchahan Formation), with high volume of organic matter, are the major source rock of Dehram Group reservoir in South Pars Gas Field. Residual oil (bitumen) were seen on some parts of Kangan Formation core. According to some reports, Lower Triassic (Kangan Formation) sediments is a possible source rock, for Kangan reservoir contents (gas and condensate). Recent geochemical study on tar and asphaltic oil of Kangan Formation (not reservoir contents), shows that these oily materials were produced from shaly and shaly- limestone layers of Kangan Formation, but due to low TOC content , poor source rock potential, and low maturity level (late diagenesis) of Kangan, this Formation is incapable of production of huge amount of gas and condensate. It seems that the produced hydrocarbons from shaly and limestone layers of Kangan Formatin, has no relation with hydrocarbons generated from Silurian shales.
N. Khodaei; M. H. Adabi; S. A. Moallemi; M. Moradpour
Abstract
The Kangan Formation is a carbonate-evaporate sequence that is considered as a part of the largest carbonate reservoir in the South Pars Field at Persian Gulf. Petrography analysis led to the recognition of 5 different dolomite types: such as dolomicrite, dolomicrospar, dolospar, dolomite cement and ...
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The Kangan Formation is a carbonate-evaporate sequence that is considered as a part of the largest carbonate reservoir in the South Pars Field at Persian Gulf. Petrography analysis led to the recognition of 5 different dolomite types: such as dolomicrite, dolomicrospar, dolospar, dolomite cement and saddle dolomite. Elemental studies on dolomicrite and dolomicrospar samples show a relative increase of Sr and Na and relative decrease of Fe and Mn in comparison with the dolomicrosparite samples. It is notable that the oxygen-carbon isotope trend in dolomite samples are due to slight influence of meteoric diagenesis (about dolomites type I, II and III) and burial diagenesis (about dolomites type IV and V). The dolomicrites have been undergone slight meteoric diagenesis, although they have formed in sabkha environment. The source of Mg for dolomicrites is the magnesium of seawater and interstitial waters equilibrium with seawater and on the other hand probably for the coarser grain dolomites in the Kangan Formation is connate waters and basinal brines. Based on the heaviest oxygen isotope in dolomicrite samples, paleotemperature of depositional environment of the Kangan Formation was around 44.5°C.
