Geopersia
Year:2011 | Volume:1 | Issue:2|Papers Count:7

Permeability prediction problem has been examined using several methods such as empirical formulas, regression analysis and intelligent systems especially neural networks and fuzzy logic. This study proposes an improved and novel model for predicting permeability from conventional well log data. The methodology is integration of empirical formulas, multiple regression and neuro-fuzzy in a committee machine. A committee machine, a new type of neural network, has a parallel structure in which each of the applied methods (experts) has a weight coefficient showing its contribution in overall prediction. The optimal combination of the weights is obtained by a genetic algorithm. The method is illustrated using a case study from a heterogeneous Upper Jurassic carbonate reservoir in Balal oil Field, Persian Gulf. For this purpose, one hundred fifty-one samples from the intervals comprising core and well log data were clustered into eighty-one training sets and seventy testing sets to evaluate the validity of the models developed. The results of this study show that the genetic algorithm optimized committee machine has provided more accurate results than each of individual experts used.

Feldspar grains, as a significant provenance indicator, of two terrigenous formations from Central Iran, the Upper Red Formation, and Moghan area, Zivah Formation, are used for provenance determination and the study of transportation and depositional history. The Upper Red Formation (URF) is volumetrically the most important siliciclastic unit of the Central Iran and Zivah Formation (ZF) represents the most important hydrocarbon reservoir in northwest Iran. Two representative sections of the URF in the southern foot hills of Central Alborz and three representative sections of the ZF in the northern foot hills of Talesh Mountains are investigated in this study. The sections represent best outcrops of the formations in their basin margin. Chemical composition, zoning and twining are the main characteristics of the feldspar grains used for this study. Results from facies analysis of the formations show that ~68% of the URF and ~73% of the ZF facies are suitable for this study, for having considerable amount of feldspar grains (>5% detrital feldspars).Results from the study of chemical composition, zoning and twining of detrital feldspars of the URF facies indicate dominance of intermediate (andesite to dacite) volcanic rocks in their source region. In the same way, volcanic sources with dominance of basic to intermediate rocks (basalt to andesitic basalt) are determined as provenance of the ZF facies.These results point to the Eocene age volcaniclastic-dominated Karaj Formation (green series) as major source of the URF facies and the Eocene volcanics of the Talesh Mountain (Talesh series) and Middle Eocene Peshtasar Basalt as major sources of the ZF facies. Comparison of the composition, zoning, and twining of the detrital feldspars with those of proposed sources indicate higher alteration/modification of the feldspars of the URF facies. Greater alteration/modification of the feldspars of the URF facies, despite their less humid and warm depositional condition, is related to more rapid deposition and shorter transportation of the ZF facies. These results indicate greater subsidence of the ZF basin and/or uplift of its source region than that of URF. Greater structural deformation of the Moghan area than Central Alborz during development of the studied formations is understood from this study.

Stylolite networks and their insoluble residues (IR) are among the major concerns and the fundamental controls on the mining and processing of sedimentary decorative stones, largely made from dolomitized limestones. They are mainly used, as natural rock blocks and polished slabs, to construct and decorate floors and walls of buildings and monuments.Representative quarries in Khur areas, east of Esfahan Province, central Iran, are selected for this study in order to evaluate the type and geometry of the stylolite networks in differentially dolomitized limestones and their control on the quality of the mined rock blocks and processed polished rock slabs. Field observation, examining the mined wall-rock cuttings in quarries, and petrography of the selected thin sections of Upper Cretaceous Haftoman Formation were performed with a comparative study of thickly developed, rudist-bearing rudstones-grainstones to bioclastic packston wackestone microfacies. What is typically considered in this study is evaluating the geometry of stylolite networks (cells), as they merge and result in a 3D network, rather than laterally continuous single stylolites. This study highlights the primary lithofacies types and diagenesis controls on the mining and processing of sedimentary decorative stones and documents that under relatively ideal tectonic conditions, slightly dolomitized, thick-bedded, relatively clay-free (<10% IR), mud-dominated packstones-wackestones provide the best shallow marine, carbonate lithofacies for preparing polished rock slabs. This is in contrast to clay-rich argillaceous limestones with dissolution seams or stylolite networks and pervasively dolomitized, grain-rich platform carbonate lithofacies characteristically with stylonodular, brecciated and chalky textures.

In this paper, the role of molecular diffusion in mobilization of water flood residual oil is examined. A moving mesh method is applied to solve the moving interface problem of residual oil blobs swelling by Co2 diffusion through a blocking water phase. The results of this modeling are compared with experimental results of a 2D glass micro model experiment. Although, the solution method is applied for a 1D system, a good agreement between numerical and experimental results validates the solution method. In this method a fixed time step is proposed. Furthermore, the results of this method have been compared with the results of the Grogan's finite difference method. This supposed that, the mesh network is fixed and time step increasing will be continued until the oil-swelling equal to one spatial step size.

For obtaining reservoir petro physical properties, for example porosity, non-destructive methods such as X-ray computed tomography, CT, seems to be precise and accurate. Porosity is deducted from the CT image with a single scan via different techniques, such as pore space detection by image segmentation techniques then correlation with porosity.More than one hundred samples with carbonate lithology have been scanned and analyzed in this study which leads to empirical correlation used for porosity calculation from CT data. The samples mainly grouped as dolostone, limestone and carbonate with respect to their mineral contents, having porosity ranges between 4.56 to 30.5 % and permeability from 0.25 to 3350.8 md. The results showed that the effect of atomic number is higher than the density on CT image. It is because density and atomic number in carbonate mineral (calcite and dolomite) show diverse relations. Thus, the assumption of known lithology would be a large source of error. A good linear relationship exists between the porosity and CT no. according to the developed correlations.

Sulphosalts in the system AgSbS2-AgAsS2 have been experimentally investigated using dry methods. The solid solutions which form between α-miargyrite and smithite have different structures. The EPMA data for the solid solution series show that there is an inverse relation between Sb and As. The cell parameters of the solid solution between α-miargyrite and smithite increase up to about 50% of AgSbS2 substitution in the smithite structure and then reveal a structural phase transition as a function of composition. Electron diffraction (TEM) data for α-miargyrite is consistent with the space group A2/a, but for the compositions Ag (As0.1Sb0.9) S2 and Ag (As0.3Sb0.7) S2, the phases do not show good Laue zones and Kikuchi lines and the symmetry could be either monoclinic or triclinic. The variation in the DW factor derived from the EXAFS spectra for the first shell of S atoms surrounding As in Ag (As0.3Sb0.7) S2 tends to be smaller than for AgAsS2 indicating that the As environment in Ag (As0.3Sb0.7) S2 is more ordered than in Ag (As0.5Sb0.5) S2 and AgAsS2. This ordering indicates that with more substitution of Sb in AgAsS2, the monoclinic (A2/a) Ag (As0.5Sb0.5) S2 collapses around As atoms to a probable low-monoclinic or triclinic structure.

The Aligoodarz granitoid occurs in Sanandaj-Sirjan Zone (SSZ), Western Iran. Tonalite, granodiorite and granite are the main rock types cropping out in the area. Comparison of Aligoodarz granitoid with Dehno and Boroujerd granitoids reveals several similarities in their chemical characteristics. Thus, the above mentioned granitoids can be assigned as a co-genetic magmatic suite, in which plutons evolved from a parental magma, with fractional crystallization being the main mechanism for magma evolution. Samples with lower SiO2 content from different areas, are not similar in composition, and indicating varying degrees of mineral accumulation and trapped interstitial melts. These granitoids are compositionally similar to normal I-type granitoid rocks originated from continental arcs. Compared with the primordial mantle, they are enriched in Large Ion Lithophile Elements (LILE) and Light Rare Earth Elements (LREE) over High Field Strength Elements (HFSE) and Heavy Rare Earth Elements (HREE). This feature together with relative depletion of Ta, Nb, Ti, and P confirm derivation of these granitoids from a crustal source region in continental arc environment.