Gazovaya promyshlennost’ № 02 2022

The study sets out the main features of producing horizons at the Chayandinskoye oil, gas and condensate field (Republic of Sakha (Yakutia)): low formation temperatures, high salinity of the residual reservoir water, risk of hydrate formation in the bottom hole formation zone. It determines the hydrate formation conditions depending on the pools’ pressure-and-temperature conditions, formation gas composition, and residual water salinity. It also analyses the specific features of hydrate formation in the bottom hole formation zone associated with underbalance, gas cooling during throttling, and water vapor condensing from the filtered gas with residual water salinity near the borehole reduced. According to the thermodynamic analysis, reservoir drawdown of hydrate-free operation is estimated to be 1.0–1.2 MPa for long-life gas well operations at Chayandinskoye field. It is feasible to further clarify this value for the field’s production wells, which will require additional specialized research.

Currently, there is no officially approved methodology in Russia that would regulate the problem of selecting well screen for various conditions of production wells. The selection is made, at best, by analogy. Such a situation, concerning one of the main elements of wells design, which is responsible for the wells flow rate and determining its service life-time as a whole, is unacceptable. Due to this fact, in order to improve the efficiency of hydrocarbon deposits development, a method for selecting well screens is proposed which was applied in the Chayandinskoye oil, gas and condensate field located in the Lensky District of the Republic of Sakha (Yakutia). The main feature of the described method lies in providing an individual approach to each productive horizon, based on the core geological-mechanical studies and the reservoir granulometric characteristics. Previously, the authors of the article determined that the main criteria for the selection of well screens should be provision of the required mechanical strength when installing screens in a well and its subsequent operation; corrosion resistance throughout the entire design life-time of operation, minimum pressure losses while maintaining the suffusion stability of rocks in the near-screen zone; maintenance of the well stable operation during the entire period of its operation due to the design of the screen and the use of methods to restore productivity. A detailed study of the productive horizon nature and the well design features followed by comparison with the allowable drawdowns made it possible to determine the type of well screens and their characteristics for each productive horizon of the Chayandinskoye oil, gas and condensate field.

The article considers the temperature regimes of gas gathering systems at the later stage of field development in the Far North. This stage is characterized by decreasing flow rates in wells and pipelines of gas gathering networks, which enhances the effect of ambient temperature on the operating modes of a gas field. During the winter period, the temperatures of gas flows can fall below zero (Celsius). Combined with the liquid accumulation in gas gathering networks, this can lead to hydrate and/or ice depositing in the gas gathering systems. Thus, ice and/or hydrate deposits were formed in some wells and gathering pipelines at the Medvezhye, Urengoyskoye, and Yamburgskoye fields. Besides, ice and hydrate formation occur in the coldest months, when it is important to ensure maximum gas recovery and its reliable supply to consumers, which further aggravates the situation. In the technological simulation of gathering pipeline operation modes, declining gas production led to longer pipeline sections with below-zero (Celsius) flow temperatures, so the areas dangerous in terms of ice deposition were shifted from the field plant to well clusters. The most common methods for preventing ice and hydrate deposition (such as inhibitor supply, purging, and heating) do not always allow for restoring the operation of field pipelines. Hence, some technical solutions are proposed to reduce the risks of ice and hydrate formation and improve the efficiency of gas gathering systems in winter season.

The Barents Sea shelf has significant resource potential and prospects for mineral stock development. The geological zoning of oil and gas fields divides the region into the Timan-Pechora Basin, West Barents, and East Barents petroleum provinces. Since the Timan-Pechora Basin province continues into the sea, the sea part is associated with prospects of discovering oil pools formed by Paleozoic source rock, and the Barents Sea shelf is forecast to have gas and gas-condensate pools generated by organic matter in Mesozoic rocks. At the same time, some gas- and oil-condensate accumulations are discovered within the Pechora Sea, including Kolguyev Island. Besides, liquid hydrocarbon pool development is predicted in the near-edge zone of the Barents Sea basin. The article demonstrates the diversity of compositions and properties of hydrocarbon fluids from the Barents Sea fields based on compiled research results by various companies for different years. The fluids are classified into eight types based on their physical and chemical properties and form a scale from dry gases to supergene heavy oils. It is noted that the condensate and oil densities’ change with depth does not follow the patterns found in most regions. Regarding source matter type, the pool distribution observed neither corresponds to the theoretical vertical zonation. Based on the geochemical ratios calculated for gas and liquid parts of the hydrocarbon systems, five source matter types are suggested. They are formed by different-age source rocks in the spatially isolated kitchen areas. Some secondary genesis indicators are revealed in the fluid composition of the main gas-condensate pool of the Shtokman-Luninsky region. The source matters were different: immature Triassic gas-source deposits of humic organic matter type and catagenetically mature Paleozoic source rocks of mixed organic matter type.

The article considers the problems that arise when applying technological processes of natural gas liquefaction in the Far North of Russia on the example of the Yamal LNG project. Based on the results of the advantages and disadvantages analysis of the technologies applied, general patterns of development of large-capacity processes are identified and an alternative scheme for the liquefied natural gas production is proposed. The models of the described technological trends are built, their brief structural comparison is carried out, energy costs are compared under conditions of various raw materials loads and ambient temperatures. The latter is most relevant for the Yamal Peninsula, the climate of which is characterized by a wide range of air temperatures in summer and winter. According to the constructed graphs, the relationships between the efficiency of natural gas liquefaction cycles and the technological characteristics of the processes are revealed. The features have been identified that will improve the energy efficiency of the developed technologies in arctic conditions, such as the type of the main cryogenic heat exchanger, the compressor drive used, and the refrigerants used.

The most dangerous emergency situations which may occur during liquefied natural gas storage in cryogenic tanks with vacuum-powder insulation are a breakage of the internal vessel tightness by a liquid outside spillage, followed by its subsequent evaporation and vapor ignition. Such development of events can be avoided if the liquid spillage outside is eliminated by using full containment tanks. The presented article considers the technological diagram of a full containment tank with a bypass safety device, which was patented by PJSC GAZPROM. To check the operational capability of the technological diagram, as was assigned by Gazprom VNIIGAZ LLC, a model of a 10 m3 full containment tank was developed by Cryoservice Research and Production Enterprise JSC, which was later tested on liquefied natural gas by the specialists of All-Russian Research Institute of Fire Protection of the Ministry of the Russian Federation for Civil Defense, Emergencies and Elimination of Consequences of Natural Disasters in Orenburg. The results obtained showed that when imitating the violation of the internal vessel tightness, the spilled liquid was retained in the inter-wall space. The pressure in them (the vessel and the inter-wall space), as well as its differences, remained within the acceptable limits. When liquid was spilled into the inter-wall space with vacuum-powder insulation, the temperature of the casing wall decreased to cryogenic values. The tank’s gas discharge system ensured the safe removal of cold vapors of liquefied gas in an emergency situation. Based on the results of the tests, a conclusion was made, saying that the technological diagram of a full containment tank for liquefied natural gas with a bypass safety device is operational and provides fire safety in case of the liquid spillage into the inter-wall space of the tank.

The cost value for operating electrochemical corrosion protection systems depends on the significant amount of energy-consuming equipment located in a large servicing territory. Meanwhile, the energy efficiency of some part of the cathodic protection equipment is not optimal. In certain groups of objects, such as gas distribution networks and multi-line corridors of main pipelines, electrochemical protection equipment with low energy efficiency is located unevenly, thus making it possible to identify separate zones with an increased concentration of such equipment. A significant amount of cathodic protection installations cannot be subjected to a fully integrated analysis of their state using classical methods by the maintenance services. To solve this problem, a special technique has been developed by the authors of the article. The results obtained during this technique use show that, on the site plan, zones of an increased density of cathodic protection installations accumulation with low values of the output current are fixed by geoinformation analysis methods. Some of these installations are turned off in standby, providing compensation for the shutdown by increasing the operating equipment capacity from the same zone. This technique is implemented in the software algorithms of the geographic information system. In total, at the first stage of the developed technology implementation, it is planned to switch off 567 cathodic protection installations, putting them into the reserve ones, which makes 12.1 % of the total number of installations of Gazprom transgaz Kazan LLC, being in operation. It is shown that the planned measures don’t have a negative impact on the corrosion protection level of buried pipes. Implementation of the developed measures to optimize systems electrochemical protection is economically feasible, the recoupment period is 2 years and 5 months. The economic effect of the 2-year use of the equipment is expected to be 17.8 million rubles per year.