During coreflooding under stationary conditions, permeability is determined by the Darcy formula; thus, the apparent permeability is determined, which characterizes the average hydraulic conductivity of the core, but does not take into account the processes occurring at the microlevel. Transient processes during fluid injection regime change are important for understanding the evolution of permeability and underlie such phenomena as permeability degradation and its hysteresis. Our paper presents the coreflooding methodology and the results showing that during changes in injection conditions, the permeability of samples can significantly decrease due to the migration of colloids. In the developed methodology, coreflooding conditions exclude the influence of other factors on permeability, such as creep, the chemical reactions of rocks and fluids, and chemical mobilization of colloids. It has been established that the decrease in permeability occurs only when fluid is injected through the core, which is indirect evidence of pore blockage by colloids. The article also attempts to evaluate the effect of pore pressure on the sensitivity of the porous medium permeability to the amount of injected fluid. A decrease in pore pressure leads to a more intense decrease in permeability during injection, which most likely indicates additional mobilization of colloids, while the narrowing of pore channels does not affect permeability. Analysis of coreflooding results showed that porous media with lower permeability are more sensitive to colloid migration and pore pressure changes. It has also been found that the sensitivity of porous media to colloid migration is greatly affected by the pore pressure gradient, while media with higher permeability are less sensitive to colloid migration.

No abstract

A set of techniques for well treatment aimed to enhance oil recovery are considered in the present study. These are based on the application of elastic waves of various types (dilation-wave, vibro-wave, or other acoustically induced effects). In such a context, a new technique is proposed to predict the effectiveness of the elastic-wave well treatment using the rank distribution according to Zipf 's law. It is revealed that, when the results of elastic wave well treatments are analyzed, groups of wells exploiting various geological deposits can differ in terms of their slope coefficients and free members. As the slope coefficient increases, the average increase in the well oil production rate (after the well treatment) becomes larger. An equation is obtained accordingly for estimating the slope coefficient in the Zipf 's equation from the frequency of the elastic wave. The obtained results demonstrate the applicability of the Zipf 's law in the analysis of the technological efficiency of elastic-wave well treatment methods.

The research reveals that during selection of a method to increase oil recovery it is necessary to take into account rheological features of fluid movement through the formation, effect of capillary forces and heterogeneity of reservoir properties of the productive formation in thickness and along the bedding. Low-frequency wave impact, which is used to increase production in oil fields, is considered. At low-frequency impact new fractures appear and existing fractures in rocks increase in size. The greatest increase in porosity and permeability of rocks occurs at an impact frequency up to 10 Hz. Dynamics of oscillation amplitude during wave's movement in saturated porous medium is studied in the paper: essential attenuation of amplitude occurs at distance up to 1 m from borehole axis. With increase of frequency from 1 to 10 Hz the intensity of amplitude's attenuation decreases. The technology was tested on a well in Perm region (Russia). The actual permeability value was 50 % higher than the predicted value. According to the results of hydrodynamic investigations processing, it was noted that the greatest increase of permeability took place near the wellbore, while away from the wellbore axis permeability remained almost unchanged. In order to refine the mathematical model for prediction of wave impact on rock permeability it is necessary to take into account interconnection of pore space structure, change of adhesion layer, as well as to study transfer of particles during vibration.

Пермский национальный исследовательский политехнический университет, Пермь, Россия Описаны проблемы, связанные с качеством крепления скважины. Освещены основные негативные последствия некачественного разобщения пластов. Одним из решений данной проблемы является применение расширяющихся тампонажных составов для повышения герметичности крепи скважины и, соответственно, качества разобщения продуктивных и водоносных горизонтов. Рассмотрены механизмы процессов расширения тампонажных составов. Проведен обзор основных типов расширяющих добавок для тампонажных растворов. Выявлено, что наибольшая величина линейного расширения обеспечивается при оксидном механизме расширения за счет ввода добавок оксида кальция и оксида магния. Оксидное расширение обусловлено образованием гидроксидов соответствующих металлов, оксиды которых занимают меньший объем, нежели продукты гидратации. Основной проблемой, сдерживающей широкое применение оксидного типа расширения, является высокая скорость гидратации исходных веществ, что приводит к образованию гидроксидов в подвижном цементном тесте, тем самым исключая расширение цементного камня. С целью получения расширения в пластичном, не набравшем высокую прочность цементном камне проведены исследования и определено влияние определенных химических реагентов на скорость гидратации оксида кальция. Выявлены наиболее оптимальные компонентные составы расширяющих добавок на основе оксида кальция для тампонажных растворов. Установлены требования к технологическим параметрам базового тампонажного раствора. Определен компонентный состав и разработана рецептура базового тампонажного раствора на основе портландцемента марки ПЦТ-I-G-CC-1, который станет основой для расширяющегося тампонажного состава. Для регулирования водоудерживающих и реологических показателей тампонажный раствор модифицирован добавками. В качестве водоудерживающей и структурообразующей добавки предлагается использовать гидроксиэтилцеллюлозу, в качестве пеногасителясиликоновый пеногаситель. Допускается ввод поликарбоксилатного пластификатора для повышения подвижности и текучести тампонажного раствора. Ключевые слова: тампонажный раствор, оксидное расширение, качество крепления, цементный камень, цемент, скважина, восстановление герметичности крепи, модифицирующие добавки для тампонажных растворов.