Experimental estimation of specific surface area of bazhenov oil shale and factors controlling its increase

Results of Bazhenov formation deposits organic matter complex investigations to assess its oil generation potential and maturity are presented. Researches were performed by Rock-Eval pyrolysis, rock structure analysis using scanning electron microscopy and organic matter transformation and distribution in the bulk of rocks using luminescent microscopy. As a result of the research, the general pattern for the Bazhenov formation kerogen thermal maturity variability along Western Siberia was confirmed, and the high maturity areas delimitation around the Salym high and the Krasnoleninsky arch was significantly specified. The areas of anomalously high maturity are not related to regional patterns of sedimentation. The possible influence of thermal maturity on the unconventional reservoirs with kerogen porosity formation in the Bazhenov formation and the features of their distribution were established. High thermal maturity that refers to the end of oil window is one of the main condition for the Bazhenov formation oil capacity formation, but knowledge of maturity change through the area pattern is not a sufficient condition for unconventional reservoirs including that with kerogen porosity retrieval.

The work is devoted to interpretation of results received from a wide complex of laboratory petrophysical investigations of the Bazhenov formation rocks collected from the core in several fields in Western Siberia. The main goal is comparison and substantiation of evaluation results received from using of different methodologies of petrophysical rock properties measurements. It is necessary for identification of the most adequate and applicable methodology of petrophysical investigations realization for the Bazhenov formation. The Bazhenov formation draws attention of researchers for many years [2, 3, 4, 6]. It significantly differs from usual sedimentary rocks by both composition and physical properties. Lithological and petrophysical investigations of the Bazhenov formation core from different fields showed that it is represented by clayey-silty porous-fractured and fractured reservoirs characterized primarily by high variability of reservoir properties in the formation's distribution area. The majority of reservoirs have low porosity (1–2%) and permeability of less than 0,1 mD. However in some well columns there are interlayers with porosity reaching 16%. Standard approaches of traditional in Russian Federation petroleum well logging practically don't allow quantitatively estimate the composition and reservoir properties of natural reservoirs. That's why it is extremely essential, on the one hand, to engage methods providing possibility of quantative definition of rock mineral-component composition and enhancing accuracy of its reservoir properties, effective porosity and permeability, and, from the other hand, to prepare new approaches for interpretation of the proposed complex. The problem of effective porosity and oil and gas saturation determination is complicated by the fact that these natural reservoirs contain big amount of kerogen while mineral component consists of a silicon dioxide, clayey minerals, pyrite, albite, carbonaceous minerals. Selection of them could be defined by the core but it is essential to estimate its weighting in column of a definite well. Therefore main factors that should be kept in mind while evaluating porosity are complex mineralogical rock composition, shale content and high content of organic matter (reaching 40% by mass). Existing methodology of reservoir identification and its properties evaluation by well logging don't rely on detailed investigations of the Bazhenov formation composition. This situation is explained by an attempt to average accumulated data of the Bazhenov formation in the whole Western Siberian oil and gas basin not always confirming it by results from a real object core investigation. In the present work there are results of core investigations in some areas allowing adjusting the interpretation of well logging to evaluate reservoir properties of the Bazhenov formation.

The results of experimental studies of the macrocomponent and microcomponent compositions of pore solutions in the bituminous siliceous shales of the Bazhenov Formation (BF) in Western Siberia with total organic carbon (TOC) contents up to 12.63% (“normal rocks”) and the silty sandstones of the “anomalous” section of the BF with TOC contents no higher than 0.63% (“anomalous” rocks) are presented. The studies of water extracts from core samples were performed. It was found that the pore solutions in the rocks of the “normal” BF rocks are sodium sulfate–bicarbonate, whereas the solutions in the “anomalous” rocks are sodium bicarbonate–chloride. The following tendencies were noted in the pore solutions of both “normal” and “anomalous” rocks compared with the oceanic water: (a) increase in Mn, Co, Ni, Cu, Zn, Mo, Sb, Cd, Ba, V, and Cr concentrations to varying degrees; (b) elevated Cs, Pb, and Ti concentrations in pore solutions of “anomalous” rocks only; (c) reduced Li, B, Rb, and Sr concentrations. A direct correlation between Li, B, Ba, Sr, U, Mo, Cd, Sb, and Ni concentrations in the pore water and total organic carbon (TOC) contents in the rocks was established. The concentrations of V, Cs, Sb, Rb, Ti, and Mn in pore waters display a close to inverse correlation with TOC content in rocks. The content of Ba in the pore solutions of the “normal” BF rocks equals or exceeds the Sr content, which is abnormal compared with formation water in most oil fields and with ocean water and is attributable to the specific features of organic-rich mudstone accumulation, considering that the Sr content in the “anomalous” rocks of the BF is two times higher than the Ba content, which is closer to their usual ratios in most natural waters.

Multi-scale rock surface area quantification—a systematic method to evaluate the reactive surface area of rocks

Research subject. Anomalous sections present in the oil- and bituminous-bearing Bazhenov Formation (BF), in the central areas of the West Siberian basin, are considered to have emerged due to the injection of plastic pulp masses from the sedimentation slope into weakly lithified basal deposits. The aim of this research was to evaluate the as-emerged rocks by analyzing their composition and structure at the macro- and micro- levels. Materials and methods. We investigated reference well sections in the Imilor deposit to elucidate the interaction of the rocks with sandy-clay landslide pulp, their volumetric weight, ductility or brittleness, caused by the presence or absence of a continuous mineral frame. Results. According to core and well logging data, nine regional packs were distinguished in the BF stratotype. The maximal depth of the natural hydraulic fracturing of the rocks is explained by their high bulk density. The lateral movement of the main slump mass is found to have occured on the stratigraphic level of the first and second BF packs, since these layers possessed zero-buoyancy with regard to the injected pulp under their approximate equality in terms of bulk density. The traces of such active movements were revealed in rock samples from the walls of horizontal cracks in the form of clay intrusions having a thickness of about 0.1 mm and strict orientation of all micro-crystals along the walls and the flow. It is shown that inclusions of the rocks under investigation (bazhenits) in BF are generally characterized by their initial stratigraphic sequence, which is confirmed by the sequential disintegration of proto-bazhenit plates during the process of BF up-floating on a growing sedimentation slope. During the disintegration of the lithified and non-lithified layers of radiolarits, the former crumbled due to alternating loads, while the latter - mobile radiolarites - were represented by the hydraulic fracturing liquid, along with quicksand. Conclusion. A detailed petrographic study of core samples from intact deposits of the Bazhenov and George Formations and their anomalous sections have allowed their layer-by-layer comparison to be confirmed the landslide hypothesis and to be derived the information on the degree of lithification of the BF strata during the formation of its anomalous sections.

The surface areas of amorphous mixed oxides and their relation to potentiometric titration

Nitrogen adsorption isotherms, along with the BET model for interpretation, are recommended for estimating biochar surface area. The frequently measured small surface areas of biochars contrast with their high sorption and cation exchange capacities. We hypothesised that water adsorption provides a better tool for estimating the surface area of biochars. Although adsorption energy also appears to be a valuable surface characteristic, there is a lack of studies on this subject. We studied the surface areas and adsorption energies of three waste deposits – peat, willow dust and biochar prepared from these materials at different temperatures – using nitrogen and water vapour adsorption isotherms. The BET model accurately described all water vapour adsorption isotherms but failed for some nitrogen isotherms. Alternative methods for estimating surface areas and adsorption energies were proposed in cases where the BET model did not apply. Nitrogen adsorption was typically much lower than water vapour adsorption, and the estimated surface areas reflected this. However, nitrogen adsorption energies were significantly higher. Nitrogen surface areas increased with pyrolysis temperature, while water vapour surface areas decreased. The surface area estimated from nitrogen adsorption was generally much lower than needed to accommodate the surface-charged groups responsible for the cation exchange capacity of biochars.

SEM petrography of dispersed organic matter in black shales: A review

Russia is one of the recognized world leaders in oil and gas, but exhaustion of traditional deposits required to seek a new resource base commensurate with the scale developed by major oil and gas provinces. As an equivalent alternative is considered a huge potential for the world's largest shale formation - Bazhenov Formation, which is spread along the whole Western Siberia. Sweet, in the case of the creation of new incentives for its development, Russian oil production will lead to a new level. Development of stocks look attractive because Bazhenov formation developed in areas with existing oil infrastructure, directly at the producing fields, so you can rely on lower costs. A unique feature of the Bazhenov Formation is the high oil saturation. Moreover, it is of high quality - light, sweet crude and without other harmful impurities. However, the lack of a clear understanding of the problems of geologists Bazhenov does not allow the government to offer transparent mechanisms to reduce the tax burden on subsoil users who are willing to carry out development only if it will be profitable. This still does not exist a unified classification of unconventional hydrocarbons and confusion of terms often creates illusions about the resource potential and production prospects. Thus, mining companies and investors planning to undertake the development of the Bazhenov Formation, faced with the enormity of uncertainties and risks. The final opinion on the prospects and opportunities of the Bazhenov suite of commercial oil production from this horizon can be formed on the basis of analysis of log data, core analysis, well tests and geomechanical research that will eventually pick up the development of efficient technologies - a kind of golden key, which will allow truly discover the wealth formation. The article focuses on the problems associated with the technology development and the development of the suite. The analysis of the geological structure, lithology and reservoir properties (FES) Bazhenov Formation in the Khanty-Mansi Autonomous District.

An integrated methodology for evaluating the prospective non-conventional oil resources is presented here, and applied to real situations in Western Siberia. The method involves 1) a detailed analysis of geochemical data on the oil shale, 2) considerations on the mineralogy of the shale and surrounding beds and 3) integrated 3D petroleum system modelling of the oil and gas generation, retention and expulsion. The integrated study involving Depositional system, Geochemistry and Petroleum system modeling demonstrates that the Bazhenov shales in central Western Siberia have stored 20 to 30% of the total generated oil, 50% being expelled upward in neokomian and 20-30% downward in the Upper Jurassic. The amount generated represents only 20 to 30% of the total potential. Geochemistry and Petroleum system modeling allow identifying th According to the Bazhenov source-rock characteristics, estimates of the productivity under economic condition can be given, and compared with the Bakken oil Shales from USA

The Bazhenov shale, the unique object of concentration of nonconventional reserves of hydrocarbons, is the main petromaternal rock of the central part of the West Siberian lowland. It is traced practically in all its territory, both by seismic cuts, and according to correlation schemes of wells’ cuts. According to some experts’ estimates, about 15% of oil resources in Western Siberia occur in siliceous and clay rocks of the Bazhenov shale, where at the beginning of 2016 more than 90 fields with inflow of oil from clay rocks are registered. Owing to high inhomogeneity of the layer, low filtrational and capacitor properties, high water repellency, geological and other features, the Bazhenov shale on Western Siberia fields either has not been developed, or oil production conducted as trial tests. The main goal of this article is the presentation of researches’ results and development of the Bazhenov shale on two perspective fields of Western Siberia.

The composition of rocks of the Bazhenov and Abalak formations in Western Siberia is described. Correlations of the concentrations of the major and minor components in rocks with the concentrations of minor elements and organic material are shown. Study of the concentration of minor elements allows us to determine the conditions of sedimentation: redox potential, hydrogen sulfide contamination, and the source of sedimentary material. The results show that rocks of the Bazhenov Formation were formed under the conditions of low fluxes of clastic material, a reduced environment, and a periodically occurring hydrogen sulfide mode.

JSC RITEK was planning to drill a horizontal well in oil shales of the Bazhenov Formation in the area of wells 100H-101H in the Middle Nazym field, Western Siberia. This area is characterized by high risks of borehole instability. Several wellbores have been already lost mostly because of wellbore wall shear-failure in the intervals of unstable shales at the base of the Frolov Formation, just above the Bazhenov Formation. 3D geomechanical modeling was undertaken to optimize horizontal well planning and drilling and minimize the risks of wellbore instability in the area. Core sampling and testing and acoustic logging with registration of Stoneley wave were carried out on the pilot well to evaluate mechanical properties of rocks, identify intervals of vertical (VTI) anisotropy and calibrate 1D Mechanical Earth Model. Well data and seismic inversion results were used to build structural model, populate properties and run 3D reservoir geomechanical modeling with calculation of full stress tensor in each grid cell. The 3D modeling results were applied to wellbore stability analysis for the planned horizontal well. High borehole instability in the 90-m interval at the base of the Frolov Formation is resulted from combination of factors: mechanical properties of the rocks, horizontal stresses distribution and well trajectory. The Frolov shales in this interval have the lowest uniaxial compressive strength and highest VTI anisotropy, and, consequently, the higher magnitude of horizontal stresses with respect to the adjacent intervals. The increase of well deviation and angle of attack from 40° to 80° in the unstable shale interval results in drop of uniaxial compressive strength of the rocks and narrowing of safe mud weight window. To minimize drilling risks, trajectory, construction and mudweight program were optimized for the planned horizontal well 101H-BIS. Additional casing section of 7”, borehole deviation in a range of 55°-75° and mud weight of 1.57 g/cm3 have been suggested for the high-risk interval of unstable weak shales at the base of the Frolov Formation. Vertical anisotropy analysis on the basis of core testing and acoustic well log data proved for the first time the Bazhenov Formation contains both anisotropic and isotropic highly brittle intervals that is relevant for the completion planning. 3D geomechanical modeling taking into account VTI anisotropy of shales provided new estimation of horizontal stresses distribution that reflects heterogeneous response of units of variable mechanical properties on the applied stress.

Summary In this study, we consider maturity trends for Tmax and other parameters measured by Rock-Eval pyrolysis for one of the largest organic-rich oil shale formations - the Bazhenov Formation, Western Siberia, Russia. The natural maturity trends reflecting generation, migration, and accumulation of hydrocarbons were compared with artificial maturation experimental data. The experiments showed similar maturity trends for samples with different TOC content, which allowed us to consider the Bazhenov Formation as an entire petroleum system with the common source of organic matter and common maturity trends. Described maturity trends and obtained correlations between maturation and pyrolysis parameters could be used for advanced maturity evaluation for the Bazhenov formation. The suggested approach could also be useful in geochemical studies of other source rock formations.

In the Bazhenov Formation, framboidal clusters and nodular pyrite formed in the dysoxic–anoxic interface within organic-rich sediments. Some nodule-like pyritized bituminous layers and pyrite nodules are similar to pyritized microbial mat fragments by the typical fine laminated structure. Framboidal pyrite of the Bazhenov Formation is enriched in redox-sensitive elements such as Mo, V, Au, Cu, Pb, Ag, Ni, Se, and Zn in comparison with the host shales and nodular pyrite. Nodular pyrite has higher concentrations of As and Sb, only. Strong positive correlations that can be interpreted as nano-inclusions of organic matter (Mo, V, Au), sphalerite (Zn, Cd, Hg, Sn, In, Ga, Ge), galena (Pb, Bi, Sb, Te, Ag, Tl), chalcopyrite (Cu, Se) and tennantite (Cu, As, Sb, Bi, Te, Ag, Tl) and/or the substitution of Co, Ni, As and Sb into the pyrite. On the global scale, pyrite of the Bazhenov Formation is very similar to pyrite from highly metalliferous bituminous black shales, associated, as a rule, with gas and oil-and-gas deposits. Enrichment with Mo and lower Co and heavy metals indicate a higher influence of seawater during formation of pyrite from the Bazhenov Formation in comparison to different styles of ore deposits. Transitional elements such as Zn and Cu in pyrite of the Bazhenov Formation has resulted from either a unique combination of the erosion of Cu–Zn massive sulfide deposits of the Ural Mountains from one side and the simultaneous manifestation of organic-rich gas seep activity in the West Siberian Sea from another direction.