Evaluation of Absolute Permeability in Heterogeneous and Anisotropic Porous Media Using the Lattice Boltzmann Simulations

Abstract: This paper presents a systematical study of the effect of porosity, pore-level heterogeneity and anisotropy on the absolute permeability of digital images of porous media. The main goal is to develop an analytical formula that estimates permeability as a function of these three parameters at once. Permeability is assessed based on numerical simulations using the lattice Boltzmann equations. Digital models of porous media are generated by a combined method consisting of Monte-Carlo and quartet structure generation set (QSGS) algorithms. Increase in heterogeneity negatively affects permeability. With an increase in porosity, the effect of heterogeneity on flow properties decreases. There was a linear decrease in permeability during the transition between favorable and unfavorable anisotropy. The influence of anisotropy is most pronounced in samples with high porosity and monotonically reduces with decreasing porosity. Heterogeneity negatively influences on the sensitivity of flow properties to changes in anisotropy and independent on porosity

Secondary dolomitization of the Domanik black shales as an indicator of gas-water hydrocarbon-containing fluids upward migration in the Tatarstan territory

© 2020 IOP Publishing Ltd. All rights reserved. The share of unconventional oil reserves is high in Russia and Volga-Ural region, including shale oil reservoirs. It contains around 65% of the total volume of hydrocarbon reserves in region, according to various data. Shale hydrocarbons are widely used in Russia. The main part of the Domaniki oil black shale is confined to carbonate-siliceous carbonaceous complexes of the Domanik horizon of the Francian stage of the Upper Devonian system. According to previous studies in the Domanik formation sedimentary complexes of the Volga-Ural oil and gas province, two types of rocks are distinguished - the Domanikites themselves and Domanikoids. Domanikites contain from 5 to 20% organic matter. Both types of carbonaceous rocks have a practically similar lithological composition. The difference between them lies in variations in siliceous component content and number of authigenic minerals. If content of very fine-grained silica was determined by primary sedimentation factors, then authigenic minerals are indicators of secondary lithogenesis processes. In this work, an attempt is made to compare organic matter content with dolomite mineralization, which is an active agent in mineral formation

Fluid inclusions in vein calcite from the productive reservoirs of the Astrakhansky gas condensate field

© 2020 IOP Publishing Ltd. All rights reserved. Fluid inclusions from calcite veins were studied the Astrakhanskoye gas condensate field. It was done for the identify the conditions for the formation of oil reservoirs located in bioclastic recrystallized limestones with vertically oriented fractures. Samples were selected from the core material of one studied well in interval 4215-4217 m. Two types of syngenetic inclusions were found in calcite: gas and gas-liquid inclusions. The homogenization temperature of gas inclusions is from -16.9 to 40 °C. Studying the gas phase by Raman spectroscopy show the presence of methane and hydrogen sulfide. Carbon dioxide, ethane, and propane were found in smaller quantities. The homogenization temperature is 100-130 °C of two-phase fluid inclusions. Probably, it is close to the temperature of the vein calcite aggregates. The aqueous phase of inclusions is represented by solutions of magnesium chloride. The gas-phase was not studied by Raman spectroscopy because of mobility. The total composition of inclusion gases in calcite is represented mainly by carbon dioxide, methane, and hydrogen sulfide, according to gas chromatography. Ethane, propane, and isobutane are present in smaller amounts. The concentration decreases from ethane to butane. Also, ethylene, propylene, and butylene were identified in very low concentrations. A characteristic feature of hydrocarbon gases is a decrease in concentrations from ethane to propane and from propane to butane, and it is typical for gas condensates

Facies variability of pennsylvanian oil-saturated carbonate rocks (Constraints from bashkirian reservoirs of the South-East Tatarstan)

© 2020, Georesursy LLC. All rights reserved. One of the strategic ways of the old oil-producing regions is to further prospecting for potentially promising areas for hydrocarbon. One of these exploration areas is the Volga-Ural region. These reservoirs consist of Carboniferous carbonate rocks, which contain high viscous hydrocarbons and are characterized by complex facies architecture and reservoir properties influenced by diagenesis. The high degree of facies variability in the studied area does not allow reliable distribution of potential reservoir rocks not only between different areas but even within the same oil field. Based on textural and compositional features of carbonate facies, 5 main facies associations were identified and characterized with respect to the depositional settings in the Bashkirian basin. The facies associations correspond to: distal middle ramp facies, open marine proximal middle ramp facies, high-energy innershoal facies, inner ramp facies of restricted lagoons, facies of affected by subaerial exposures. From west to east in the study the following trends in facies characterare identified: 1) a decrease open marine middle ramp facies and in the total thickness of the Bashkirian sections; 2) an increase in evidences of sub aerial exposures; 3) a decrease in the proportion of potential reservoir rocks. A general shallowing of the depositional setting was identified in an eastward direction, where potentially promising reservoir facies of shallow high-energy environments were replaced by facies of restricted lagoon and facies affected by subaerial exposures and meteoric diagenesis (palaeosols, dissolution). The applied approach based on detailed carbonate facies analysis allows predicting the distribution of potentially promising cross-sections within the region

Sedimentary diagenesis and pore characteristics for the reservoir evaluation of Domanik formations (Semiluksk and Mendymsk) in the central part of Volga-Ural petroleum province

The Upper Devonian Semiluksk (Domanik) and Mendymsk carbonate successions have been identified as the most promising unconventional oil and gas deposits in Russia's Volga-Ural petroleum province. Three lithofacies were identified: limestones, organic matter-rich siliceous carbonate, and dolomitic limestones/dolomite. Their sediments are thought to have accumulated in the relatively deep-sea shelf depositional environment. According to X-ray analysis, calcite is the most common mineral phase in the limestones. The siliceous carbonate rocks' major mineral phases were identified to be quartz, followed by calcite. The rocks have relatively poor reservoir qualities, with porosity ranging from 0.1 to 5% and permeability ranging from 0.01 to 10 mD. Petrographic examination of thin sections reveals four major types of pores: 1. interparticle pores, which are abundant in all of the examined lithofacies; 2. intercrystalline pores formed between dolomite crystals and the very fine components of the siliceous carbonate rocks. 3. vugs as a result of leaching, and 4. fracture as a result of tectonic and/or diagenetic events. Plotting the obtained data from the petrographically examined thin sections on the ternary pore plot diagram resulted in the identification of six pore facies and their related diagenetic patterns. Pore facies 1 depicts the pores that formed during the depositional process. Pore facies 4 displays moldic pores. The vugs are represented by pore facies 6. Pore facies 2 is a mixture between pore facies 1 and pore facies 4. Pore facies 3 is a mixture between pore facies 1 and pore facies 6. Pore facies 5 is a mixture between pore facies 4 and pore facies 6. Comparing the petrographic results and the identified pore facies show that pore facies 6 have touching pores and they played the most important role in improving the reservoir quality. The pore facies 4 which have separate pores have the most influence in the reduction of the reservoir quality. The diagenetic origin secondary pores are the most pores identified in the studied carbonate section. This reflects the strong modification of the pores by the diagenetic overprinting. The massive dissolution that forms the touching vugs, and the dolomitization process are the most diagenetic processes that affect the pore system within the studied rocks

Features of the transformation of visean quartz sandstones under the influence of water-oil fluids

Research subject. This article analyses specific features of secondary transformations of quartz grains under the influence of water-oil fluids on the example of the Tulsky and Bobrikovsky oil-saturated quartz sandstones of the Demkinskoye oil deposit in the south-east of Tatarstan. Materials and methods. The research was carried out using the methods of optical microscopy, x-ray diffraction and electron paramagnetic resonance (EPR). Results. On the example of the Tulsky and Bo-brikovsky oil-saturated Visean quartz sandstones, we analysed the influence of water-oil fluids on rocks and features of the secondary transformations of quartz grains in the Demkinsky oil field in the southeast of Tatarstan Republic. In the oil-charge stage, the spatial redistribution of silica was realized. Quartz grains dissolved in the sole and middle part of the re-servoir, precipitating in the form of chalcedony in the top part of the reservoir. The dissolution of quartz grains was promo-ted by micro defects concentrated on their periphery. The dissolution was triggered by both plastic deformations of minerals at the contacts and an increase in the alkalinity in the pore space up to pH = 9–10. Chalcedony aggregates were formed in the intergranular space of oil-saturated sandstones. Depending on the nucleation point of the siliceous substance and silica concentration in pore fluids, either single spherulitic or agate-type aggregates were formed. According to EPR, the studied chalcedony aggregates have a high content of paramagnetic E’-centres. This was caused by a deficiency of oxygen in the mineral-forming fluid during chalcedony precipitation. Conclusions. Chalcedony precipitation underwent in acidic con-ditions, which led to silica-type metasomatism in the top part of the reservoir followed by substitution of muscovite grains by morphological fibrous chalcedony. Metasomatism affected the grains of both detrital muscovite and muscovite present as inclusions inside quartz grains. This process indicates the manifestation of surface and bulk diffusion of silica, affecting all clastic components

Mineralogical and lithological properties of Domanikites from the south-east of Tatarstan Republic

© 2020 IOP Publishing Ltd. All rights reserved. The article was described main types of rocks - mudstones, carbonate-siliceous rocks, containing organic matter and carbonate breccia, based on detailed analysis of rock samples from Semiluksky horizons of Upper Devonian black shale formations, Volga-Ural region, Russian Federation. Different structures and texture features, mineral composition, and content of organic matter characterized selected types of rocks. Only in the carbonate-siliceous type of rocks is the high content of organic matter, about 9%. It was found direct dependence between the content organic matter and content in rocks silica minerals (quartz and chalcedony). Such dependence caused by joint precipitation silica minerals and accumulation of organic matter in the seafloor in conditions of active seepage of hydrothermal fluids. The presence of an abundance of biophilic elements in ascending fluids led to an explosion of biota and widespread of silica organisms. This hypothesis doesn't disagree with any authors but considers the significant contribution of fluid factor to the deposition of Semiluksky formations