Integrated approach to the typification and localization of deposits of the anomalous section of the Bazhenov formation of the Frolov oil and gas region

Introduction. The subject of the study of this work is the deposits of the anomalous section of the Bazhenov formation (ASB) of Western Siberia, the disturbed occurrence of which was recorded by 2D, 3D seismic exploration and borehole data at many fields of the Frolov oil and gas region. The research area unites the company’s assets in the KhMAO and the Tyumen region, which are part of the large hydrocarbon cluster “ZIMA”. Aim. In order to typify various complexes of rocks of the Bazhenov formation and further localization of deposits, a comprehensive core analysis, GIS and seismic studies were performed. Materials and methods. According to the results of lithological study of the core and petrophysical interpretation of logging diagrams, have been identified various types of rocks in the interval of the Bazhenov formation. According to the results of the interpretation of the seismic survey materials, contoured zones that differ in the wave pattern by different coherence of the axes of common phase. The revealed differences in seismic sections compared with borehole data and geological bodies mapped based on the obtained patterns. Results. Based on a comprehensive interpretation of the core, GIS and seismic studies, established the zonality of the distribution of various types of deposits of the Bazhenov formation, the relationship of the development of ASB zones with the introduction of Early Cretaceous sedimentary bodies and showed the introduction of detrital material from the overlying rocks. Conclusions. The authors of the article conclude that the development of anomalous sections of the Bazhenov formation involves several stages of the introduction of landslide bodies of overlying rocks, according to the gradation of Neocomian clinocyclites in the north-west direction. Within the study area, mapped three large landslide bodies in the Bazhenov formation interval, each of which was formed an internal zonality and because of the introduction of rocks from the overlying interval.

Forecasting the operation of wells in the Bazhenov formation based on a modified dynamic material balance model

Background. Predicting the dynamics of the Bazhenov formation is an important task. Traditionally, it is carried out using geological and hydrodynamic modeling, i. e., solving the direct problem of hydrodynamics. However, for shale reservoirs, this approach is not possible, oil production is a derivative of geology to a lesser extent than technology. Industrial net production rates can be obtained from non-reservoirs in the usual sense. The system of technogenic fractures forms a reservoir associated with oil-saturated rock and the properties of such a system are described by too many parameters with high uncertainty and a number of assumptions [3–7]. On the other hand, there are forecasting methods based on solving the inverse problem of hydrodynamics. Having a sufficient amount of development data, it is possible to predict the dynamics of work based on statistical dependencies [9] or proxy material balance models. The purpose of this work. The purpose of this work was to create a convenient methodology for calculating oil production from the reservoirs of the Bazhenov formation. Methodology. The paper proposes and tests a method for predicting the dynamics of oil, liquid and gas production for wells in the Bazhenov formation based on a modification of the CRM dynamic material balance model (Capacity-Resistive Models — volume-resistive model). Results. The method was tested when calculating the technological indicators of development for the object of one of the fields located in the KhMAO and showed its efficiency, which allows us to recommend it as a basis for drawing up project documents as an alternative to building a hydrodynamic model (GDM).

Feasibility of the Bazhenov Formation Reservoir Hydrodynamic Model

Опыт изучения нефтяных месторождений, приуроченных к отложениям баженовской свиты, показывает, что продуктивность нефтенасыщенных пластов является существенно неоднородной как по площади, так и по разрезу месторождения. Выявление зон повышенной продуктивности в отложениях баженовской свиты является одной из первоочередных задач по вовлечению в разработку значительных, но трудноизвлекаемых запасов, приуроченных к отложениям баженовской свиты. С целью выявления зон повышенной продуктивности необходимо определять типы пласта-коллектора, выявлять особенности энергетического состояния залежи нефти, строить гидродинамическую модель залежи нефти в баженовской свите. The studies of the oil fields confined to the sediments of the Bazhenov formation shows that the productivity of oil-saturated formations is significantly heterogeneous both in terms of the area and thickness of the productive formations. Identification of higher productivity zones in the Bazhenov formation sediments is one of the primary problems enabling to development of the large, but hard-to-recover reserves confined to the sediments of the Bazhenov formation. To identify such zones, it is necessary to determine the type of the reservoir, identify the features of its energy state, and build a hydrodynamic model of the oil reservoir in the Bazhenov formation.

Features of filling reservoirs with hydrocarbons in the territories with a low maturity of the oil and gas parent rocks (a case study of Jurassic hydrocarbon traps in the Uvat district)

The article is devoted to the results of an analysis of geological factors that had a great influence on the filling of Jurassic traps with hydrocarbons. Based on the results of paleotectonic analysis, three key stages of reconstructions of the structural plans of sedimentary cover deposits were identified. Each stage was characterized not only by the appearance of new traps in the interval of Jurassic deposits, but also by the sinking of rocks of Bazhenov formation to a certain depth. It is revealed that in most of the territory of the Uvat district, Bazhenov formation didn't have time to fully realize its hydrocarbon-generating potential. In the Central and Eastern regions it entered the main zone of oil formation only in the Paleogene. Since the development of the relief of modern structural plans of Jurassic deposits in this area occurred in several stages, both the formation of traps and the lateral migration of hydrocarbons also occurred in stages. The first stage of migration occurred at the boundary of the lower and upper Cretaceous, the second stage occurred at the beginning of the Paleogene. As a result, the combined influence of lateral migration of hydrocarbons and the gradual formation of local structures in different areas of the Uvat district led to selective filling of Jurassic hydrocarbon traps.

Residual Water Saturation of Source Rocks of the Bazhenov Formation Western Siberia, Russia

The article presents a new method of determining the residual water saturation of the Bazhenov Rock Formation using synchronous thermal analysis which is combined with gas IR and MS spectroscopy. The efficiency of the extraction-distillation method of determining open porous and residual saturation in comparison with the developed method which are considered in detail. Based on the results of studies in the properties of the Bazhenov Rock Formation, a significant underestimation of the residual water saturation in the existing guidelines for calculating reserves was found, and the structure of the saturation of rocks occurred to be typical for traditional low-permeability reservoirs. The values of open porous and residual water saturation along the section of the Bazhenov Formation vary greatly, which also contradicts the well-established opinion about the weak variability of the rock properties with depth.

Increasing the Productivity of Horizontal Wells Through Multistage Hydraulic Fracturing Using a Working Fluid Based on a New Biopolymer System

According to the US Energy Agency (EIA), Russia is the world leader in terms of the volume of technically recoverable "tight oil" resources (U.S. Department of Energy, 2013). To convert them into commercial production, it is necessary to create cost-effective development technologies. For this purpose, a strategy has been adopted, which is implemented at the state level and one of the key elements of which is the development of the high-tech service market. In 2017, the Minister of Energy of the Russian Federation, in accordance with a government executive order (Government Executive Order of the Russian Federation, 2014), awarded the Gazprom Neft project on the creation of a complex of domestic technologies and high-tech equipment for developing the Bazhenov formation with the national status. It is implemented in several directions and covers a wide range of technologies required for the horizontal wells drilling and stimulating flows from them using multi-stage hydraulic fracturing (MS HF) methods. Within the framework of the technological experiment implemented at the Palyanovskaya area at the Krasnoleninskoye field by the Industrial Integration Center "Gazpromneft - Technological Partnerships" (a subsidiary of Gazprom Neft), from 2015 to 2020, 29 high-tech wells with different lengths of horizontal wellbore were constructed, and multistage hydraulic fracturing operations were performed with various designs. Upon results of 2020, it became possible to increase annual oil production from the Bazhenov formation by 78 % in comparison with up to 100,000 tons in 2019. The advancing of development technologies allowed the enterprise to decrease for more than twice the cost of the Bazhenov oil production from 30 thousand rubles per ton (69$/bbl) at the start of the project in 2015 to 13 thousand rubles (24$/bbl) in 2020. A significant contribution to the increase in production in 2020 was made by horizontal wells, where MS HF operations were carried out using an experimental process fluid, which is based on the modified Si Bioxan biopolymer. This article is devoted to the background of this experiment and the analysis of its results.

Operation Features of Wells with an Extended Horizontal Wellbore and Multistage Hydraulic Fracturing Operation in Bazhenov Formation

Wells with extended horizontal wellbore (HW) drilling with multistage hydraulic fracturing (MHF) is necessary for commercial oil production from Bazhenov formation (Vashkevich et al., 2015; Strizhnev, 2019). Today the maximum HW length for Bazhenov formation wells is 1500 m (Strizhnev, 2019, Korobitsyn et al., 2020). In international practice the maximum HW length for shale oil production is around 3000-400 m (Rodionova et al., 2019). Pump Down Perforator (PDP) technology is used for MHF: a liner is run in hole and cemented, then perforation and hydraulic fracturing (HF) are successively performed by stages at equal distances from the end to the beginning of HW to create a branched system of fractures in Bazhenov formation. Performed HF stages are isolated with special packer plugs (insoluble blind, dissolvable blind, insoluble with seat for dissolvable ball or dissolvable with seat for dissolvable ball)) (Mingazov et al., 2020). Consequently, the fluid inflow into the well is occurred along whole HW and the flow rate increases from monotonically from the end to the beginning of HW and has maximum value at last HF stage. The numbers of HF stages are about 24-30 (number of perforating clusters - 100) at one well in Russia and 50 in the world (Alzahabi et al., 2019). One of important parameter during HF is the speed of HF fluid injection into the formation. Tubing outer diameters 114-140 mm. are used in HW to increase the injection rate and reduce friction losses in the well. The flow rate of HF fluid in this case reach to 14-16 m3/min (Ogneva et al., 2020; Astafiev et al., 2015). Monobore wells construction is planned to use with outer diameter 140 mm. A stinger is used as sealing element between tubing and liner to minimizing risk of HF liquids leaks into the annulus (Astafiev et al., 2015). As a result, the inner well diameter from wellhead to bottomhole is around constant in the process of MHF. The pressure in the hydraulic fractures and the collector near fractures after MHF is highly exceeded the initial reservoir pressure. Hence wellhead pressure after MHF in water filled well is about 100-150 bar (Jing Wang et al., 2021). This fact significantly limits downhole well operations because of requires killing (tubing change, let down ESP, etc.). These works are required heavy well killing fluid because of high overpressure. It is undesirable because of it can reduce the fracture conductivity, worse well bottom zone properties and reduce well productivity. Therefore, the well is working at flowing mode in initial period usually until the reservoir pressure in the drainage area is decreased at the hydrostatic level or below (Jing Wang et al., 2021). After that the well can be killing using technical water with a density of 1.01 – 1.07 g/sm3 (the use of well-killing fluid with a density higher than 1.1 g/sm3 is undesirable). The possibility of well flowing working depends on properties of collector and reservoir fluid: High gas-oil ratio (GOR) and reservoir conductivity help well flowing until reservoir pressure drop off hydrostatic pressure.

Basin Modeling as a Tool for Research of Regional Oil and Gas Generation Processes and the Possibility of Replacement of Oil and Gas Riches Illustrated through Traygorodsko-Kondakovskoye Oil Field

The article presents the results of two-year of research aimed at replenishing the resource and raw material base of the northwestern part of the Tomsk region. The practical application possibilities of basin modeling at the prospecting and exploratory stages of geological study of the subsurface are illustrated. The research was divided into two phases. The first of them has sub-regional coverage and includes an area of 25,000 km2 bounded by the Chkalovsky oil and gas condensate field in the southeast and the administrative boundaries of Tomsk Oblast in the northwest. The section is confined to the Alexandrovsky arch, covers part of the Koltogorsko-Nyurolsky chute and the eastern periclinal of the Nizhnevartovsky arch. At the first stage, a three-dimensional model of oil-and-gas bearing basin formation was created, the tasks of which were to replenish the history of generation and formation of ideas about the ways of hydrocarbon migration. The basin submergence has been reconstructed here and the thermal flow history has been restored. The uneven intensity of heat flow at the bottom of the sedimentary cover over the area is explained by tectonic processes and is complicated by a massive granitoid intrusion. In JSC "Tomsk Petroleum institute", the knowledge base of geochemical features of oil-and-gas source rocks and oils of Western Siberia was formed for years, which allowed to use their own kinetic spectra for the surveyed region. To calibrate the paleotemperatures, both the optical characteristics of vitrinite coals and the indicators of the geochemical properties of organic matter of the Bazhenov formation (4/1 MDBT and Tmax) were used. As a result, the conclusion about the presence of two generation centers of different nature was made, the time and volume of oil generation by organic matter of the Bazhenov formation were predicted. Next, the modeling parameters of hydrocarbon migration and accumulation are described. Modeling shows that the primary migration occurs due to the emergence of abnormally high pore pressure during the generation of hydrocarbons and fluid autofracture of the oil and gas source rock. The results of calculations of secondary migration by two different methods are compared. Despite a number of limitations, the results obtained show a fairly high convergence to real data. At the second stage, on the basis of the regional (parent) model a local daughter model of the formation of the Traygorodsko-Kondakovskoye field within the area of 480 km2 covered by 3D seismic exploration was plotted. The rationale for the necessity and description of the results of additional special geochemical studies of fluids and oil source rock, carried out before starting to build a detailed model of the local stage, is given. The article outlines the basic parameters and gives the differences between the local model and the parent model. Conclusions are made about the possibility of assessing the conductive properties of fault in the formation of deposits. The prediction of trap saturation and resource potential assessment is the result, the achievement of which reduced the risks of geological exploration and formed the recommendations for further geological study of the subsurface.

Investigation of Source Rock Heating and Structural Changes in the Electromagnetic Fields Using Experimental and Mathematical Modeling

The paper presents the results of an experimental study of heating and the structural resultant changes of source rocks under the influence of the electromagnetic field in the microwave and radio-frequency ranges. The samples from the Bazhenov Formation (West Siberia, Russia) and the Domanic Formation (Ural, Russia) have been tested. It is shown that samples from these formations demonstrate very different heating rates at the same electromagnetic field parameters and the their heating rate depends on the type of the electromagnetic field (radio-frequency or microwave) applied. The temperature of the Bazhenov Formation samples reaches 300 °C within one hundred seconds of the microwave treatment but it slowly rises to 200 °C after twelve minutes of the radio-frequency influence. The samples of the carbonate Domanic Formation heat up more slowly in the microwave field (within two hundred seconds) and to lower temperatures in the radio-frequency (150 °C) than the Bazhenov Formation samples. The study of the structure of the samples before and after experiments on the electromagnetic treatment shows fracture formation during the heating process. Numerical simulations of heating dynamics of source rock samples have been based on a simple mathematical model of the electromagnetic influence and main features of heating for different types of source rock have been revealed. The opportunities for application of electromagnetic heating for oil source rock recovery are discussed.