Gas-saturated Zone Research Articles

Impact of gas arising from gas hydrate decomposition on the effective permeability of bottom sediments of the Arctic shelf: a laboratory simulation

Relevance. The necessity to investigate the mechanism of gas (methane) flow occurring during decomposition of gas hydrate formations within the layers of bottom sediments. This process is evident through substantial releases of methane bubbles in extensive shallow regions of the Russian Arctic shelf and has the potential to alter the equilibrium of atmospheric methane, a critical greenhouse gas. Aim. To quantitatively investigate, within the context of gas transport in bottom sediments, the impact of free and bound gas within the pores on the nonlinearity of filtration flows. Methods. The model samples with filtration properties similar to those of the bottom rocks of the East Siberian Arctic shelf. During the experiments, a specific amount of gas was injected into the saturated model sample, followed by the measurement of its effective permeability during a slow decrease in pore pressure gradient. The obtained curve was interpreted within the framework of the threshold gradient model. Results. The experiments yielded curves showing the dependency of the threshold gradient magnitude on gas saturation for several samples. It was found that the threshold gradient linearly increases with the growth in gas fraction within the pore space. Already at a gas fraction of approximately 0.02, this value in the experiments reached 0.01 MPa/m, corresponding to the hydrostatic pressure gradient in water. This suggests that even areas with relatively low gas saturation may be impermeable to convective fluid flow. This possibility should be considered when creating models for bubble gas transporting through the rock layers of bottom sediments. Furthermore, the existence of gas-saturated zones with threshold gradients can significantly impact the vertical profile of pore pressure and lead to a reassessment of the depth of gas hydrate stability zones.

Structural and seismic attribute analysis of the Paleocene carbonate reservoir from the Balkassar Field, Potwar Plateau, Pakistan

The structural and seismic properties of the Paleocene carbonate reservoir are re-evaluated, using 3D seismic data multi-attributes, to improve reservoir prediction accuracy rarely documented earlier. This study highlights a number of relevant post-stack seismic attributes for understanding the structural setup and seismic properties of a carbonate reservoir. The structural analysis was carried out using seismic interpretation, combined with multi-attribute analysis for prospect actualization and generation of a 3D structural model to determine the structural aspect. The structural interpretation reveals the presence of faults and an asymmetrical anticlinal structure demonstrating a four-way closure, confirming compressional tectonics. The high amplitude anomaly (-6 to 12) combined with the RMS attribute (23 to 32) suggests bright spots in the Paleocene carbonate reservoir and gas saturated zone, the variance attribute (0.05 to 0.03) highlights the presence of two major faults, and the lower instantaneous frequency demonstrates the presence of hydrocarbons. The attribute results indicate that the Lockhart Limestone possesses good reservoir potential as revealed by DHI (bright spot), gas saturated zone and a trapping mechanism supported by four-way structure closure in the region and can help to understand analogous carbonate reservoirs in similar geological settings around the world.

Integration of a Low Gas-Saturated Zone in Creating a 3D Model of the Medvezhye Field

3D geological modeling is an integral part of reserves estimation and project documentation for the development of gas and oil fields. The developed 3D geological model of the Cenomanian productive complex including the low gas-saturated zone of the Medvezhye field represents a combination of data from the drilling of 350 wells, the structural features of the reservoir, permeability properties determined on cores, seismic surveys, and the results of geophysical well surveys. Based on examining the available well logs recorded in the Medvezhye field wells, the low gas-saturated zone is integrated into the construction of the 3D geological model of the Medvezhye field of the Cenomanian productive complex. A total of three models are constructed, and a 400*400*0.4 m grid is recommended for further hydrodynamic modeling. A comparison of the three grids suggests that a more detailed model delivers more thorough results, however, heavy models cannot be applied to hydrodynamic modeling. Resource estimations do not differ across the three grids significantly.

Predicting the Development of a Low Gas-Saturated Zone of the Medvezhye Field Based on Geological and Hydrodynamic Modeling

Given the rising water cut and reduced gas flow rate at large fields in Western Siberia, the issue of further development of productive formations of such fields is urgent. The factor of efficient use of natural resources also needs to be considered for extraction to be the most productive. The study is devoted to the construction of a 3D geological model of the PK1 layer of the Medvezhye field and a 3D hydrodynamic model created on its basis. Four project variants for the development of the transition zone of the PK1 formation of the Medvezhye field are proposed. The forecast period spans from 2023 to 2060.

APPROACHES TO STUDYING THE EFFECT OF GAS COMPONENT ON THE MECHANICAL PROPERTIES OF FROZEN SOILS

Studies of recent decades have shown that the gas component plays a significant role in the structure and properties of frozen soils. This is indicated by a significant influx of greenhouse gases into the atmosphere from the permafrost; gas emissions leading to accidents at boreholes; the formation of gas emissions craters, etc. These processes are determined by the mutual influence between the characteristics of the gas component and the indicators of the physical and mechanical properties of frozen soils, which have not been studied enough to date. The formation mechanisms of gas-saturated zones are considered; the influence of gas on the physical and mechanical properties of thawed and frozen soils is assessed; and the processes associated with the impact of gas on the soil massif are analyzed.

GEOLOGICAL AND STRUCTURAL MODELS OF FORMATION AND ACCUMULATION OF GAS IN MAN-MADE RESERVOIRS OF COAL ROCK MASSIVES

The formation of technogenic reservoirs of coal-rock massifs is determined by the depth of development, lithological features of the host rocks and the gas content of the coal-rock massif. The formation and redistribution of gas-saturated zones and migration routes in coal-rock massifs continues even now, which is associated with modern fluid migration. Gas, filling the mine workings of closed mines, creates a threat to communications, structures as a result of explosions and has a negative impact on human health.
 It has been established that the regular distribution of gaseous hydrocarbons is determined by discontinuities and confirms not only the diffusion gas saturation of the massif, but also the tempo, that is, the gas saturation of the massif through discontinuities during tectonic (tectonic-magmatic) activations. At the same time, it should be noted that geological discontinuities were not the “transport arteries” of gaseous hydrocarbons not throughout the entire space. For most of its strike, coal and rocks in the zones of discontinuities are folded, and there is almost no gas transmission. The worked-out space of active mines is a new technogenic reservoir suitable for the accumulation of gaseous hydrocarbons, the thickness of which exceeds the thickness of the coal seam. The active processes of gas migration in the exhaust space are indicated by the study of the residual gas component, in the mixture of which helium, hydrogen and quantitative changes in hydrocarbon gases (C2 - C6) were found.

Explosive Processes in Permafrost as a Result of the Development of Local Gas-Saturated Fluid-Dynamic Geosystems

The relevance of studying explosive processes in permafrost lies in the prospect of gas production from small gas-saturated zones in the subsurface; the influx of significant amounts of greenhouse gases from frozen soils creates a threat to infrastructure. The purpose of this article is to reveal the general patterns of frozen soils’ transformation in local zones of natural explosions. The greatest volume of information about the processes preceding the formation of gas-emission craters can be obtained by studying the deformations of the cryogenic structure of soil. The typification of the elements of the cryogenic structures of frozen soils that form the walls of various gas-emission craters was carried out. Structural and morphological analyses were used as a methodological basis for studying gas-emission craters. This method involves a set of operations that establishes links between the cryogenic structure of the crater walls and the morphologies of their surfaces. In this study, it is concluded that gas-emission craters are the result of the self-development of local gas-dynamic geosystems that are in a non-equilibrium thermodynamic state with respect to the enclosing permafrost.

Estimation of porosity and facies distribution through seismic inversion in an unconventional tight sandstone reservoir of Hangjinqi area, Ordos basin

Precision porosity and facies determinations are critical in reducing drilling uncertainty and increasing hydrocarbon recoveries from heterogeneous sources. The porosity and facies distribution of the Taiyuan-Shanxi Formations (T9c-T9d), and Shihezi-1 Formation (T9d-T9e) within the Hangjinqi area are uncertain and no studies have covered the spatial distribution on a regional scale. The heterogeneous nature of coal, mudstone, and sandstone makes it challenging to comprehend the distribution of porosity and lithofacies. Also, the seismic resolution is not able to resolve the reservoir heterogeneity. Therefore, we have employed regional 3D seismic and well logs by utilizing the advanced acoustic impedance inversion to accomplish our study. Results of petrophysical analysis conducted on the well J32 showed that Shihezi-1 and Shanxi-1 Formations have potential gas-saturated zones. Crossplot analysis distinguished the lowest impedance coal from the highest impedance tight sandstone facies. The outcomes of the constrained sparse spike inversion (CSSI) reliably distinguished the coal facies from the channel-tight sandstone facies. The tight sandstone facies showed the highest impedance values as compared to coal and mudstone facies on the absolute acoustic impedance section. Impedance and porosity maps of T9d and T9e suggested the presence of a maximum porosity (8%–12% for T9d, and 5%–10% for T9e), and maximum distribution of tight sandstone facies, while T9c shows the lowest porosity (0%–6%) and lowest impedance values due to the presence of coal facies. Thick braided fluvial channels are evident on the T9d impedance and porosity maps, making it the most favorable horizon to produce the maximum gas. Whereas, T9c shows the least distribution of sandstone facies making it the least favorable. We propose that the zones of maximum porosity on the T9c, T9d, and T9e horizons can be exploited for future gas explorations.

Deep and surface factors of local gas-saturated zones formation with anomalously high gas pressure and gas emission craters in frozen soils

The article is devoted to the consideration of surface and deep factors that trigger the mechanisms for the preparation of explosive processes that form gas emission craters. The study object is local zones of gas-saturated soils with abnormally high gas pressure and gas craters. The main method used in this article is the bibliography review. The synthesis of the analyzed materials was carried out based on the geosystem approach. In the proposed work, an analysis was made of the main hypotheses of the formation of gas-saturated zones with increased gas pressure in frozen soils: 1) due to the comprehensive freezing of taliks (completely dependent on surface conditions; 2) due to the inflow of warm gas from underlying rocks into the surface layers (depending on deep sources); 3) due to the decomposition of gas hydrates contained in the permafrost (the reasons can be both surface and deep); 4) due to the joint interaction of the freezing talik and the associated deep gas inflow channel. Possibilities of realization of these or those hypotheses in real conditions are revealed. The relevance of the topic is due to the reassessment of the role of frozen soils as a screen that protects the atmosphere from the emission of greenhouse gases from the lithosphere. Evidence has appeared that this role of the cryolithozone is significantly weakened with an increase in temperature, while the frozen soils themselves can be a source of gas release.

THERMODIFFUSION SATURATION OF THE SURFACE LAYERS OF α-TITANIUM BY OXYGEN, NITROGEN, CARBON

The purpose of the study is to analytically assess the depth of the gas-saturated zone in the case of a single-component diffusion saturation of alpha-titanium with nitrogen, oxygen and carbon from a rarefied controlled gas environment. Results. Based on the analysis of the literature data, the work schematically shows the interaction of alpha titanium with the elements of implementation and presents the processes with the corresponding parameters that characterize. It is shown that the surface impurity concentration is equal to the equilibrium concentration and is established instantly and does not depend on time. Consequently, with the proposed generalized nonstationary boundary condition in the absence of diffusion of impurities into the volume of the metal, the time dependence of its surface concentration is given, determined by the intensity of surface processes. The dependence of the relative change in the microhardness in the diffusion zone of titanium due to dissolved nitrogen (without taking into account the contribution of nitride inclusions) is presented. Analytically calculated concentration profiles of nitrogen generally correlate well with the distribution of the corresponding relative changes in microhardness in the surface layer. Analytical calculations of the concentration profiles of oxygen, nitrogen and carbon in titanium at a saturation temperature of 700 °C are presented. Practical value. The results obtained will make it possible to preliminarily estimate the size of the fortified near-surface layer depending on the parameters of chemical-thermal treatment and select the optimal parameters of thermal diffusion treatment to ensure the formation of reinforced layers on products made of alpha-titanium based on elements of interstitial in order to increase the functional properties.

Application of spectral decomposition as a direct hydrocarbon indicator within the challenging rock physics environment

A study was conducted to use low-frequency amplitudes obtained through spectral decomposition as a direct hydrocarbon indicator within the geologically and seismically challenging area. An offshore data set from the Gulf of Thailand with well-known geology and good well control for both water and hydrocarbon bearing zones were used in this study. The rocks physics reveals similar P-impedance for gas and water-wet sands. Moreover, organic shales have similar Poisson’s ratio as of gas saturated zones. This makes differentiation of fluids and lithologies through post-stack seismic inversion and AVO analysis difficult. Reservoir wedge modelling, spectral decomposition of the synthetic and field data and analyses were conducted to understand the spectral decomposition response to thickness variation and reservoir fluids. Spectral decomposition was also applied on partial angle stacks (near, mid and far). Gas sands show bright amplitudes at low frequencies (from 10 to 15 Hz). However, spectral decomposition of the synthetic seismogram of the organic shales indicates that it consists of only relatively higher frequencies (greater than 25 Hz). Therefore, low-frequency amplitudes of spectral decomposition may help to identify hydrocarbon saturated zones.

Identifying gas chimneys in gas fields of the West Siberian petroleum basin via geophysical and drilling data

There are many push-down seismic anomalies (gas chimneys or pipes with a diameter of 12–15 km) in natural gas fields in the northern part of the West Siberian basin (Urengoy, Yamburg, Zapolyarnoye, Kharasavey, Yurkharovskoye, etc.). This effect is common in gas-saturated sands. The amplitude of push-downs in West Siberian fields is approximately 300–400 ms from the horizontal surface. Using well data, we have measured how much the velocity of seismic waves decreases and study the hydrocarbon presence, fluid pressure, and other information to gain a better understanding of the cause of this effect. Several wells were drilled in three different gas chimneys. All of the wells in the gas chimneys discovered vertical columnar gas deposits in Jurassic and Cretaceous terrigenous formations. Well data from the Yurkharovskoye gas field show that seismic wave velocity in the gas chimney is 40% less than that outside this object. The wells in the gas chimneys show that formation pressure in the Neocomian and Jurassic formations is 80–90 MPa, which is approximately lithostatic pressure, so high-pressured gas in the pores begins to form cracks. There are gravity anomalies above many gas chimneys identified, indicating a density deficit. Transient electromagnetic sounding data from the Yurkharov gas chimney show a columnar zone of increased electrical resistance, as in gas-saturated formations. To explain all of these observations, we suppose that the West Siberian gas chimneys (pipes) are currently active channels for the vertical migration of high-pressured hydrocarbon gases (mainly methane), forming columnar gas-saturated zones. We think that the crucial cause of push-down seismic velocity anomalies is overpressure (approximately lithostatic). We predict that some new gas fields can be related to the gas chimneys at Gydan Peninsula and in Kara Sea. Many new deep gas deposits can be found in old gas fields with gas chimneys such as Urengoy and Yamburg.

Predicting the gas resource potential in reservoir C-sand interval of Lower Goru Formation, Middle Indus Basin, Pakistan

Abstract The integrated study of seismic attributes and inversion analysis can provide a better understanding for predicting the hydrocarbon-bearing zones even in extreme heterogeneous reservoirs. This study aims to delineate and characterize the gas saturated zone within the reservoir (Cretaceous C-sand) interval of Sawan gas field, Middle Indus Basin, Pakistan. The hydrocarbon bearing zone is well identified through the seismic attribute analysis along a sand channel. The sparse-spike inversion analysis has efficiently captured the variations in reservoir parameter (P-impedance) for gas prospect. Inversion results indicated that the relatively lower P-impedance values are encountered along the predicted sand channel. To further characterize the reservoir, geostatistical techniques comprising multiattribute regression and probabilistic neural network (PNN) analysis are applied to predict the effective porosity of reservoir. Comparatively, the PNN analysis predicted the targeted property more efficiently and applied its estimations on entire seismic volume. Furthermore, the geostatistical estimations of PNN analysis significantly predicted the gas-bearing zones and confirmed the sand channel as a major contributor of gas accumulation in the area. These estimates are in appropriate agreement with each other, and the workflow adopted here can be applied to various South Asian regions and in other parts of the world for improved characterization of gas reservoirs.

ОСОБЛИВОСТІ СУЧАСНОЇ ГАЗОВОЇ МІГРАЦІЇ У ВУГЛЕПОРОДНИХ МАСИВАХ ДОНЕЦЬКОГО БАСЕЙНУ

Purpose. Investigate the change in indicators of qualitative and quantitative gas composition in coal massifs,when the state of the coal rock massif changes, including in gas-dynamic situations. Methodology. The paper uses traditional structural-geological methods, generalization methods and developed and patented by the authors of the method for determining the gas state of coal massifs on the basis of gas chromatography. Results. The change of the residual gas component in coal massifs is investigated.The stages of change of qualitative and quantitative gas composition in coal massifs at gas – dynamic phenomena are established.The ways of gas migration in coal massifs and technogenic reservoirs are determined.The concept of rate gas saturation of a coal massif, which is controlled by the action of discontinuous tectonics, is introduced. Scientific novelty.For the first time, the conditions for the formation of modern gas-saturated zones in coal massifs due to gas migration and rate gas saturation have been determined.The influence of discontinuous tectonic disturbances on the migration and accumulation of gases in coal massifs has been established. Practical significance. The influence of gas migration on the formation of gas-saturated zones in coal-bearing massifs and man-caused reservoirs of the spent space of operating mines is established,which is important to ensure the safe operation of coal mining enterprises and degassing of coal massifs. Key words: gas-bearing, gas migration, tectonic disturbances, coal massif, man-caused collectors, Donets basin.

Seismic imaging of the Solfatara crater (Campi Flegrei caldera, southern Italy): New evidence of the fluids migration pathways in the shallow structures

Seismic imaging is used in this work, to reconstruct the shallow structure of the Solfatara crater, a surface marker of deep magmatic activity inside Campi Flegrei caldera (Southern Italy). We analyze the 1D orthogonal seismic arrays deployed in NNE-SSW directions for 400 m through the Solfatara crater during the recent active experiment RICEN (Repeated Induced Earthquake and Noise) performed in the framework of the EU project MEDSUV. Seismic data have been edited in the pre-stack stage by removing the noisy traces, low-frequency noise, and reduce the ground roll phases. Then, a velocity analysis has been carried out starting from the velocity spectrum to obtain a RMS velocity model, which has been followed by NMO, residual statics, and DMO corrections. We used the post-stack Kirchhoff migration technique before the extraction of the energy, root mean square, envelope and sweetness attributes defining the highest amplitude zones, the time-gain attribute in order to interpret the deep reflectors and the variance attribute to define the faults, discontinuities, and chaotic zones. Amplitude Versus Offset (AVO) analysis has been performed to identify the gas-saturated zone using partial angle-stacks, which is a benchmark to verify the presence of gas. The main contribution of this work is to provide a more detailed and improved seismic reflection image of the shallow depth of the Solfatara crater. The reliability of our velocity model has been assessed through the use of the Vp velocity model previously obtained by the non-linear Bayesian technique. This provides a final stack showing that the shallower minor faults and the extension of the major faults represent the main pathways for the uprising fluids. We present the visual evidence for the fluids trapped in the shallower part of the crater at depths between 20 and 50 m below the surface of the crater.

Geosystems of gas-saturated permafrost

The object of this study is the geosystems of gas-saturated permafrost. Currently, the theoretical basis for examination of gas component in permafrost is practically not developed. At the same time, the theoretical and practical significance of this problem has rapidly increased in recent years. This is due to gas emissions during drilling of wells in frozen rocks, the identification of significant greenhouse gas emissions in the Arctic, the detection of previously unknown processes in the permafrost zone – the formation of craters due to gas emissions.The main method applied in the article is the analysis of research materials. The synthesis of the results was carried out on the basis of the geosystem approach. The authors are first to demonstrate that gas-saturated zones in seasonally and permafrost rocks have all the attributes of geosystems: localization in space, boundaries, morphology, individual structure and properties, development history, life cycle, hierarchy. Five types of geosystem were determined: active layer; genetic type; confined to geological structures; secondary, associated with the decomposition of gas hydrates in vivo; technogenic (due to thermal or mechanical effects on hydrated and gas saturated frozen rocks). The artcile describes promising directions in studying gas-saturated geosystems of permafrost zone, as well as  the advanced research methods.

Verification of bright spots in the presence of thin beds by AVO and spectral analysis in Miocene sediments of Carpathian Foredeep

Twin structural traps that lie within the Miocene strata of the Carpathian Foredeep that are localized above Cierpisz and Mrowla-Bratkowice highs exhibit identical bright-spot seismic anomalies, but only those associated with the Cierpisz high are profitable gas reservoirs. Bright spots can be a result of weak gas or water saturation, but also seismic interference known as tuning effect. For these reasons, it is crucial to differentiate between seismic anomalies. In this article, we present the possibilities of verification of seismic anomalies that occur within the siliciclastic Miocene sediments of the Carpathian Foredeep with the application of AVO analysis and spectral decomposition. AVO methodology enabled to limit the number of anomalies that are present in the post-stack seismic data. These anomalies, however, may also be a result of tuning which is common for the heterolithic sequences in the Miocene sediments of the Carpathian Foredeep. For classification of anomalies in the view of the above, spectral decomposition based on the Basis Pursuit algorithm was applied. Spectral decomposition enabled to divide AVO anomalies in those that are the result of gas saturation and the tuning effect. Gas-saturated zones are characterized by higher spectral amplitudes of the lower frequency range, whereas tuning effect yields higher spectral amplitudes for the higher frequency content. This relation is visible for the data set and enables qualitative differentiation for the set of seismic anomalies.

Analysis of Compositional Effects on Global Flow Regimes in CO2 Near-Miscible Displacements in Heterogeneous Systems

This study investigates the interaction of compositional effects with the flow behaviour during near-miscible (and immiscible) CO2–oil displacements in heterogeneous systems. A series of numerical simulations modelling 1D slim-tube and 2D areal systems were simulated using a fully compositional simulator. A number of grid resolutions for a slim-tube model were simulated to choose the proper level of numerical dispersion to mimic the actual physical dispersion. The corresponding 2D cases are based on a small heterogeneous sector model of dimensions 50 m × 10 m, in order that the fine-scale displacement physics can be modelled accurately. We investigated various flow regimes ranging from viscous fingering to channelling displacements within heterogeneous random correlated fields. We found that the reduced recovery is the result of a combination of differences in sweep efficiency associated with the viscous fingering and possible differences in local mixing that affect composition path. At the same time, the unstable phase flow determined by the underlying heterogeneity slows the flow in the unswept area and leads to unequal displacement performance between preferential and non-preferential routes. Specifically, lighter components have moved preferentially in high gas saturation zones, and leaving the heavier components behind in slower flow zones. In the case of channelling flow, compositional effects were less important since the permeability channel dominated the displacement. Both the ultimate oil recovery and component recovery are significantly and about equally reduced, when the underlying heterogeneity is of dominant influence. To summarise, compositional effects can have a very significant impact on the prediction of near-miscible CO2 EOR projects. Issues such as front stability, local displacement efficiency and formation of fingering/channelling during CO2 near-miscible displacement can lead to behaviour that is significantly different from immiscible flooding in these systems. The process of mass transfer between CO2 and oil can be hampered to a certain degree by unstable flow depending on the level of heterogeneity. This leads to a further reduction in component recovery, particularly of the heavier components. The complete dataset and results of this study are available online as a model case example for compositional flows in heterogeneous systems (Wang et al. in "The analysis of compositional effects on global flow regimes in CO2 near-miscible displacements in heterogeneous systems” dataset for paper SPE-190273, 2018. https://doi.org/10.17861/fc1c90bb-9d3f-4a6c-9170-7b7fe10ec7b9).

Some aspects of influence of the composition of volatile products and extracted material on grain swelling processes and volume changes of commercial coals of different rank

The course of pyrolysis process of the three industrial samples of lower, middle, and higher rank coals was studied using the TG/FT-IR technique and a laboratory unit for investigation of carbonization process by X-raying. The coal samples from the zones of plastic layer were studied by scanning electron microscopy and next extracted by a mixture of chloroform and methanol. The obtained extracts were analyzed by FT-IR and UV spectroscopies and STEM-HAADF technique.It was stated that the composition of volatile products of a lower rank coal (LRC) is characterized by the greatest relative content of saturated and unsaturated hydrocarbons in comparison with a middle rank coal (MRC) and a higher rank coal (HRC). However, a higher contribution ratio of water vapour is observed in the composition of volatile matter of HRC. It is suggested that low molecular products of destruction formed inside swelling grains of MRC can react with each other and form new compounds with a greater molecular mass. These can be macromolecules of heteroorganic compounds. The STEM-HAADF images showed that there are topological structures of various types in the material of extracts from the gas-saturated zone of coals of different rank. The presence of inorganic elements in the extracted material changes depending on coal rank. Heterorganic compounds of different shape and composition can catalyze the reactions taking place during thermal destruction of coals in a selective way. In MRC, these reactions will cause a decrease in pressure inside its swelling grains and without their substantial growth in volume. Such reactions do not take place in grains of HRC. Moreover, an increased contribution of water vapour formed during destruction can cause its adsorption inside grains and an increase in volume of swelling grains. This can be the cause for an increase in generation of dangerous coking pressure in the charge of studied HRC.

METHOD FOR ESTIMATING GAS REMAINING IN A PLATE IN THE FORM OF FREE GAS SATURATION ZONES

As it is known, when developing an oil reservoir in the dissolved gas mode, not all of the gas released from the oil comes to the surface, part of it remains in the reservoir in the form of free gas saturation zones. Not accounting for this gas can lead to a distortion of the actual situation that has developed in the reservoir and the inefficiency of subsequent measures taken to develop it. In this regard, questions arise about how to determine the presence of gas remaining in the reservoir and how to assess its amount. This article is devoted to solving the questions posed. An example is the Hassi-Mesaud field, located in Northern Africa. During the operation of the field, a weak activity of circulating water and a rapid drop in reservoir pressure were noted, which led to intensive expansion of the gas cap and the release of dissolved gas from oil. The considered field is characterized by a sharp heterogeneity and an extremely unfavorable ratio of phase permeabilities of gas and oil. If in ordinary fields the equality of oil and gas production rates in reservoir conditions is achieved at a gas saturation of 7 - 17 %, then in the field under consideration this condition is achieved at a gas saturation of 2.5 %. The task of determining the presence of free gas saturation zones was reduced to constructing a graph of the relationship between the ratio of the phase permeabilities of oil and gas and gas saturation. Such dependence was built for data obtained on the basis of core studies and field studies. The analysis of the constructed curves made it possible not only to determine the presence or absence of gas in the reservoir, but also to make an approximate assessment of the share of this gas in the total volume of the total gas released from oil.