Investigating formation resistance to fracture during operation of wells prone to plugging

In this paper, a study was conducted to determine the stability of productive formations when selecting liquid hydrocarbon reserves from them. Using mathematical modeling methods and various laws of fluid motion in a porous medium, the optimal conditioned pressure value has been established, at which the least destruction of the rock matrix will be observed. This area of research is relevant due to the fact that for the current situation, one of the most effective methods of increasing well productivity is hydraulic fracturing, which implies a significant impact on the stability of the borehole-rocks system. The obtained conclusions will make it possible to effectively plan geological and technical measures related to the impact on the rock matrix and will allow trouble-free operation of the complicated well stock

Increasing the efficiency of formation fluid extraction from highly clayey formations by affecting its structure with an electric field

Relevance. The need to evaluate the impact of a constant and alternating electric field on the physicochemical properties of various types of water, on the volumetric rate of filtration of liquids from highly clayey porous media and on the coefficient of oil displacement by water. Aim. To study the impact of a constant and alternating electric field on the hydrogen index and interfacial tension of aqueous electrolytes of various natures, as well as on porous medium permeability and the oil displacement coefficient under conditions simulating the above-mentioned formation of the Kirmakinsky formation. Objects. The experiments were carried out on a specially designed installation that allows measurements in both constant and alternating electric fields, taking into account the pressure drop. The body of the reservoir model was made of organic glass in the form of a tube with a variable length of 0.3–0.7 m and a diameter of 0.025 m with stainless steel electrodes mounted at the inlet and outlet. The research is devoted to the impact of constant and alternating electric fields on the hydrogen index and interfacial tension of aqueous electrolytes of various natures, as well as on the permeability of the porous medium and the oil displacement coefficient under conditions simulating the above-mentioned porous layer of the Kirmakinsky formation. Methods. The presence of an external electric field has a significant impact on the resulting value of the pH value and the value of the interfacial tension of aqueous electrolytes at the boundary with the hydrocarbon phase, which contributes, by analogy with the reagent treatment of oil reservoirs, to an increase in their permeability. When studying the processes of secondary oil migration in low-permeability water-saturated reservoirs, the practical absence of pressure filtration factors is noted and the dominance of diffusion-osmotic and electrokinetic factors during their occurrence is emphasized. The presence of electroosmotic movement of oil in various dispersed rocks (sand-silts and clays) under the effect of an external electric field was proven experimentally, and the possibility of displacing oil by the front of an aqueous solution of electrolytes through porous membranes of various capillary-porous nature was discussed in the work. Results. Based on the totality of the presented results, it is possible to come to an important conclusion from a practical point of view: by means of the directed action of an external electric field with regulated intensity parameters on the secondary process of oil extraction by aqueous electrolytes, it is possible to significantly increase the value of the displacement coefficient of difficult-to-permeate reservoirs, in particular high-clay reservoirs of the Kirmakinsky formation

Improvement of a well bottomhole zone treatment applying a spent sulfuric acid solution

Relevance. Caused by the need to ensure highly efficient distribution of spent sulfuric acid solutions during acid treatment of a production well bottomhole zone. The proposed method increases the efficiency of this process by growth of efficiency of production wells exploiting terrigenous limestone reservoirs in the wellbore zone. Aim. To develop and propose a method for using spent sulfuric acid solutions during acid treatment of a production well bottomhole zone, a methodology for its application. The essence of the method is that to increase the efficiency of production wells exploiting terrigenous reservoirs, solutions of sulfuric acid or its derivatives, in particular spent sulfuric acid, are used as an acid reagent. Objects. It was revealed that the surface activity of spent sulfuric acid in fresh water at the interface with hydrocarbon liquids is significantly greater than the activity of solutions of commercial hydrochloric and sulfuric acids. Based on physical and chemical studies, it has been established that spent sulfuric acid solutions can be used in acid treatment of the bottomhole zone of wells to increase formation fluid production. Solutions of hydrochloric (HCl) and sulfuric (H2SO4) acids, as well as waste – spent sulfuric acid, were used as experimental liquids. Compared to commercial acids, the spent sulfuric acid solutions have the greatest ability to interact in carbonate rocks.   Methods. Models of porous medium were created in experimental columns, which were pipes made of organic glass with a length of 0.5 m and a diameter of 0.025 m. The manufactured model of the porous medium was evacuated and saturated with fresh water, after which the water permeability was determined, then the water was replaced with acid solutions. After a certain time for the acid to react with the carbonates of the porous medium, the water permeability was again determined. The experiments were carried out at room temperature and a pressure gradient of 0.05...0.2 MPa/m. Moreover, after completion of the treatment of the near-wellbore zone in order to prevent the deposition of sediments formed in the pores as a result of the interaction of acid with carbonates, the well is put into operation after an eight-hour holding period with large depressions in the near-wellbore zone. Results. Visual observations shown that water filtration through the porous medium at high pressure gradients leads to a large removal of sediments from the porous medium. This is the consequence of an increase in the porous medium permeability after treating it with a 15% solution of waste sulfuric acid. Thus, laboratory experiments shown that the use of spent sulfuric acid solutions under certain conditions can increase well productivity

Investigation of the stress state of an elastic hollow ball during filtration of liquid through its wall

When determining the stress state of an elastic hollow ball when filtering liquid through its wall, it is necessary to solve the stress problem for the case of liquid filtration to the center of the ball with a decrease in pressure in its cavity. This case represents for us an element of the general problem of the stressed state of the annular filter behind the casing during well operation. First, the problem of liquid filtration is solved -pressure changes in the body under study are determined during liquid filtration. Then the equilibrium equation with respect to radial deformation is solved. A change in the sign of the filtration potential leads to a change in the tangential stresses on the well wall to a value equal to a tripled depression of reservoir pressure (with radial stresses equal to zero). This explains the negative effect of well shutdowns, and even more so the change in the direction of the filtration flow in the downhole part of the formation on the stability of the walls of wells, the operation of which is complicated by sand formation. The maximum difference of the main normal stresses is observed on the well wall, therefore, in order to prevent formation destruction near the bottom, a necessary condition is that the strength properties of rocks correspond to the stresses acting in this zone. When operating wells prone to plugging, it is necessary to limit the depression of reservoir pressure to the maximum permissible value when the material of the filter zone is in an elastic state throughout the volume

Experimental and theoretical research of the interaction between high-strength supercavitation impactors and monolithic barriers in water

The article describes experimental and theoretical research of the interaction between supercavitating impactors and underwater aluminum alloy and steel barriers. Strong alloys are used for making impactors. An experimental research technique based on a high-velocity hydro-ballistic complex was developed. Mathematical simulation of the collision the impactor and barrier is based on the continuum mechanics inclusive of the deformation and destruction of interacting bodies. Calculated and experimental data on the ultimate penetration thickness of barriers made of aluminum alloy D16T and steel for the developed supercavitating impactor are obtained

Special features of high-speed interaction of supercavitating solids in water

Special features of material behavior of a supercavitating projectile are investigated at various initial velocities of entering water on the basis of the developed stress-strain state model with possibility of destruction of solids when moving in water and interacting with various underwater barriers with the use of consistent methodological approach of mechanics of continuous media. The calculation-experimental method was used to study the modes of motion of supercavitating projectiles at sub- and supersonic velocities in water medium after acceleration in the barrelled accelerator, as well as their interaction with barriers. Issues of stabilization of the supercavitating projectile on the initial flight path in water were studied. Microphotographs of state of solids made of various materials, before and after interaction with water, at subsonic and supersonic velocities were presented. Supersonic velocity of the supercavitating projectile motion in water of 1590 m/s was recorded

High-speed impact of the metal projectile on the barrier containing porous corundum-based ceramics with chemically active filler

The paper presents a calculation-experimental study on high-speed interaction of the metal projectile with a combined barrier made of porous corundum-based ceramics filled with chemically active composition (sulfur, nitrate of potash) in the wide range of speeds. A mathematical behavior model of porous corundum-based ceramics with chemically active filler is developed within the scope of mechanics of continuous media taking into account the energy embedding from a possible chemical reaction between a projectile metal and filler at high-speed impact. Essential embedding of inlet heat is not observed in the considered range of impact speeds (2.5 … 8 km/s)

Recent results from the T2K experiment

Recent results of the analysis of 2:23×1021 POT data collected by the T2K long-baseline neutrino accelerator experiment are presented in this paper. It is shown that T2K is able to constrain the CP-violating phase δCP in the lepton sector with 2σ significance. Nearest plans for improving the sensitivity to δCP are also given

ИССЛЕДОВАНИЕ МЕХАНИЗМА РАЗРУШЕНИЯ ПРИЗАБОЙНОЙ ЗОНЫ ПЛАСТА ФИЛЬТРАЦИОННЫМ ПОТОКОМ ПЛАСТОВОЙ ЖИДКОСТИ И ПРЕДОТВРАЩЕНИЕ ПРОБКООБРАЗОВАНИЯ В СКВАЖИНЕ

Ссылка для цитирования: Хабибуллин М.Я. Исследование механизма разрушения призабойной зоны пласта фильтрационным потоком пластовой жидкости и предотвращение пробкообразования в скважине // Известия Томского политехнического университета. Инжиниринг георесурсов. – 2021. – Т. 332. – № 10. – С. 86–94.&#x0D; Актуальность исследования обусловлена необходимостью предотвратить разрушение пласта вблизи забоя скважин и появлением большого количества песка в пластовой жидкости при ее фильтрации в призабойную зону скважины. Решение этой проблемы позволит улучшить работу фильтрации пластовой жидкости из пласта в скважину и сократить затраты на дополнительное применение методов интенсификации притока пластовой жидкости к скважине. Цель: разработать и предложить методику, позволяющую во время эксплуатации скважин, склонных к пробкообразованию, ограничивать депрессию пластового давления предельно допустимой величиной, при которой материал прифильтровой зоны находится в упругом состоянии по всему объему. Объекты. Для определения напряженного состояния на этом участке колонны необходимо данный элемент представить в виде полого шара, который опирается на обсадную колонну. Когда снижается гидравлическое давление в материале пористой среды для процесса фильтрации пластовой жидкости, она будет расширятся при отсутствии препятствий протеканию этому процессу. Одновременно происходит повышение давления пластовой жидкости снаружи полого шара. Поэтому необходимо найти закономерности, происходящие при расширении–сжатии пористой среды в процессе фильтрации пластовой жидкости через полый шар. Методы. Наибольшая разность нормальных напряжений возникает на стенке скважины, поскольку при этом радиальные напряжения равны минимальному, а тангенциальные – максимальному значениям. Поэтому в зависимости от депрессии пластового давления и прочностных свойств закрепленной зоны возможны следующие условия эксплуатации скважины: закрепленная прискважинная часть пласта по всему объему находится в упругом состоянии; закрепленная прискважинная часть пласта по всему объему находится в пластическом состоянии. Из решения упругой задачи известно, что наибольшая разность нормальных напряжений в теле полого шара при фильтрации жидкости через его стенку к центру имеет место на внутренней поверхности, поэтому условия текучести материала шара возникнут, прежде всего, на внутренней поверхности шара. Пользуясь решением упругой задачи с учетом сжимаемости породы можно определить величину перепада давления на пласт, исключающую возможность пластического течения пластового материала, то есть допустимый перепад давления. Результаты. При эксплуатации скважин, склонных к пробкообразованию, необходимо ограничивать депрессию пластового давления предельно допустимой величиной, когда материал прифильтровой зоны находится в упругом состоянии по всему объему. Таким образом, максимальная разность главных нормальных напряжений наблюдается на стенке скважины, поэтому для предотвращения разрушения пласта вблизи забоя необходимым условием является соответствие прочностных свойств горных пород напряжениям, действующим в этой зоне.</jats:p