مجله پژوهش نفت
پیاپی 60 (پاییز و زمستان 1388)

One of the most important problems in the upstream oil industries is heavy organic and asphaltene deposition that cause to plug in formations, production surface facilities, wellbore, and flow lines. Determination of asphaltene precipitation, flocculation and aggregation mechanisms and asphaltene flocculation onset point are too important subjects in asphaltene deposition management. In this work, at first, three usual methods are applied for measuring onset of flocculation in some Iranian asphaltenic crude oils. As it can be seen, these methods are sometimes unable to give any onset point and/or their results are not always accurate enough. Here the image-processing concept is applied to develop a new effective and applicable procedure to detect asphaltene flocculation onset points. The obtained results show that the developed method not only has a good accuracy in asphaltene flocculation onset estimation especially in the most heavy and light asphaltenic crude oils, but also can be applied as powerful tool for research on kinetic growth of asphaltene particles. Also this method can be used for onset point detection and kinetic growth of asphaltene particles in live oils at high pressure and temperature.

Austenite stainless steel are inclined susceptible to cracking due to stress corrosion in Cl-ion environment; the mode of cracking can be in the form of Trans granular, Inter granular or both of them. The type of crack depends on the concentration of corroding solution, applied stress on specimen, test temperature, chemical composition and metallurgical mode of alloy. In this study, stress corrosion in sensitized 316L austenite stainless steel and the role of surface preparation on postponement of SCC crack initiation has been investigated. Test specimens were made according to ASTM G30 standard by using constant strain technique and then exposed to pure MgCl2 solution with 20, 30, and 40 wt% concentrations at 90oC. For a week, the specimens were taken out of solution everyday and their surface were studied using stereo microscope. With surface treatment such as sand blast and shot blast on specimens, it was found that residual stresses on the specimen surfaces caused crack initiation to significantly postpone in this specimens compared to specimens with untreated surface. Also, the number of cracks in surface-treated specimens were less than untreatment specimens and with an increase in chloride ion concentration in solution, crack initiation time decreases, and the number of cracks and crack depth increase. At the end of tests, the specimens were examined with electronic and optical microscopy and the effect of surface preparing on crack initiation and propagation were investigated. It was observed that, stress corrosion cracks of sensitized AISI 316l alloy initiate from specimen surface and gradually propagate in sensitized grain boundary and change fracture mechanism from Trans granular stress corrosion to inter granular.

Gachsaran Formation with 700 meters thickness is a cap rock for Asmari reservoir at Ab Teymur Oil Field in Dezful Embayment. It is mainly composed of anhydrite, halite and grey to red marl with carbonate intebeds. This research has been done based on gamma-ray logs, graphic well logs, petrography of 200 thin sections of cuttings as well as Scanning Electron Microscope (SEM) analysis with EDX attachment. The Gachsaran Formation consists of many small cycles with high frequency that may have formed during fluctuation of shallow water resulted from glacial processes, tectonic activities as well as deposition of plastic sediments and subsidence in the Zagros foreland basin. Each cycle usually begin with lagoonal limestone and marl during trangressive phase and continue with evaporites that formed during regressive phase. At this stage, sabkha is formed and deposition of anhydrite started. Salt pans are formed during the last period of regression in central part of basin and affected by flooding, concentration, and desiccation stages. Sedimentary cycles of Gachsaran Formation are very similar to many ancient and recent evaporites such as Arab Formation and recent sabkha environment in Persian Gulf.

In order to determine the maturity of the organic matter of Sarchahan Formation in northern Bandar Abbas, 15 outcrop samples were collected from Tang-e-Zakin, North Syahoo village, 70 km. from the city of Bandar Abbas. The Reflectance of Graptolites (%GRo) were measured by a reflected light microscope (MPV-SP) and histograms were plotted. The Mean Random Reflectance of these samples were 1.11% which indicate the catagenetic stage of maturity. These samples were also subjected to Rock- Eval Pyrolysis. The average Tmax for these samples is 455◦C that indicates the end of oil generation window and early stage of gas generation. The Gahkum Formation (Silurian shales) as a whole was reported as overmature and its organic matter considered to have graphitic stage of maturity. Nevertheless Gahkum Fm. was divided into Syahoo Fm. (Ordovician) and Sarchahan Fm. (lower Silurian) on the basis of their biozones. On the other hand, this study geochemically investigated Sarchahan Formation separately with the help of Rock-Eval data, TAI, elemental analysis of kerogen and measurements of graptolite reflectance (Gro%), and concluded that it is in the catagenetic stage of maturity and emphasis on the Silurian strata for future hydrocarbon exploration in Iran.

Due to majority of relative permeability in reservoir engineering studies and its dependency to some physical properties, relative permeability measurement is the most complicated task in special core analysis studies. Equilibrium in front flow during flooding and recognizing the end effect capillary pressure in relative permeability tests is very important. For this reason the usage of in-situ saturation measurement methods has a paramount importance. Also performing SCAL tests in reservoir conditions and using reservoir oil creates correct and real data for reservoir engineers to apply in reservoir models. In this study, the goal of which is the determination of in-situ saturation during flooding in reservoir conditions, first four plug samples from Asmari formation were selected and thin section studies were done to recognize the lithologies and important features. Then using relative permeability apparatus in ambient condition, the average saturations of fluids in the cores were determined by measuring the volume of fluids expelled from the samples in the flooding test and the relative permeability curves were plotted. In the next step using x-ray relative permeability apparatus, the relative permeability experiments in the reservoir conditions were performed and the value of in-situ fluid saturation and the average saturation were determined via measuring the intensity of x-ray passes through the core. The results obtained from relative permeability tests in ambient and reservoir condition were then compared. Dead crude oil from Asmari formation has been used in all experiments.

The optimization of blending of refinery products is accomplished by applying linear programming and then the problem is solved using the spreadsheet solver. This paper presents application of linear programming to blending optimization method in gasoline production. As a case study, optimization of gasoline blending in Tehran Refinery is studied by LP in order to maximize the profit.

Correlation means comparison of hydrocarbons with each other or with hydrocarbons from a source rock for genetical relations using geochemical analyses. For this propose generally, biomarkers and isotopical analyses are used. In this study, an extensive geochemical analyes such as Rock-Eval pyrolysis, Bitumen extraction and fractionatios, biomarkers and isotpical analyses were carried out on core rock samples collected from Shaly-Carbonate layers of Kangan Formation of wells B and C in South Pars Gas field. Rock-Eval pyrlysis and biomarkers analysis results reveal that the kerogen of samples were type II and III, indicating marine organic matter with a little terrestrial input. Chromatograms of saturate fraction of samples show no biodegradation alterations. The organic matter of these samples were derived from source rock(s), with clastic-semicarbonate lithology which deposited under anoxic to subanoxic depositional environment. The samples collected from well C, showing poor to moderate genetic potential and samples of well B has poor genetic potential. Maturity level of kerogen of both samples are in early oil generation zone (late diagenesis to early catagsnesis). Samples from well B showing slightly higher maturity level compare with that of well C. Well B samples show paraffinic-naphthenic and naphthenic hydrocarbon characterestics, were as the organic matter of well C, with paraffinic-naphthenic and paraffinic hydrocarbon properties. In spite of similarity of fingerprints and chemical characterization between wells C and B, it seems shally- carbonate layers of Kangan Formation is responsible for a negligible amount of hydrocarbon production. These layers act as a low quality source rock with poor potantiality.

Calculation of water saturation plays a major role in formation evaluation. Archie formula is one of the fundamental methods for calculating the water saturation of formation which contains laboratory measured parameters named Archie coefficients. When there is no access to laboratory measurement results, the Archie constants are used. Due to the heterogeneity and structural variety in different carbonate rocks, Archie constants lead to so many calculation errors. In this study, Archie coefficients have been determined for Asmari formation carbonate rocks through experiments; then some important empirical equations have been used in order to calculate Archie coefficients and compare them with the measured ones; eventually a relationship has been established between porosity and cementation factors. Results indicate that Borai formula has the best accordance with experimental data; but in order to use its formula, we must swap the coefficients with observed experimental data. Results also suggest that the experimental data have coefficient of correlation equaling 76 percent and we will witness better results provided that there are isolate samples with porosity lower than 5 percent.