Research and development of expansion agents for grouting mortars

The paper uncovers some issues related to well casing quality. The main negative consequences of low-quality bed isolation are listed. One of the solutions of this problem is application of grouts to assure structural integrity of well support and improve quality of isolation of production intervals and water beds. The machinery of grouting mortar expansion is explained. The paper reviews the main types of expansion agents for grouting mortars. It is found that the biggest values of linear expansion are obtained by oxide expansion thanks to injection of calcium oxide and magnesium oxide. Oxide expansion is conditioned by hydroxide formation of the corresponding metals which oxides possess a smaller volume than that of the hydration products. The main trouble hindering wide application of oxide expansion is a high speed of hydration of original substances, which results in formation of hydroxides in workable cement paste preventing set cement from expansion. In order to boost expansion in plastic set cement that does not feature high hardness a research was carried out and effects of certain chemical agents on calcium oxide's hydration rate were established. The optimum composition of expansion agents based on calcium oxide for grouting mortars was discovered. The requirements for technological parameters of the standard grouting mortar are established. The composition of the standard grouting mortar is specified, the PZT-I-G-CC-1 portland cement being a base for an expanding mortar. To adjust water-retaining and rheologic parameters grouts are modified by additives. Hydroxyethyl cellulose is recommended to use as a water-retaining and gelling additive, while silicone defoamant serves as a defoamant. Polycarboxylate plasticizer may be applied to improve plasticity and fluid properties

Statistical modelling of expanding cement slurry

Questions of statistical processing of results of laboratory studies of expanding cement slurry are considered. Calcium oxide with inhibitors of a hydration reaction and calcium oxide with dicalcium ferrite are used as expansion additives. Six types of expansion additives are tested. Studies are performed at the two temperature regimes such as 22 and 75 °C. Series of results is obtained. At the first stage of mathematical processing of data evaluation of differences in mean values of linear expansion values by the Student's criterion were estimated. Comparison of mean values by certain options showed that maximum influence of temperature among studied parameters belongs to CaО + ferrochrome lignosulfonate (FCLS) (99/1), minimum influence belongs to CaСО3 + FeSO4 (2:1). To consider joint influence of concentration of the expanding additive and temperature on the value of linear expansion multidimensional models are built. Model values of linear expansion were calculated from multidimensional models and then compared with experimental values. Comparisons are made in two ways. The first way is based on the total number of all the data. The second way is based on six models built on different additives. As a result, two correlation fields are obtained. Each filed has three subfields (classes). Distinguished classes are described by linear discriminant functions with help of linear discriminant analysis. An analysis of obtained discriminant functions showed that values of linear expansion in classes are formed in accordance with different mechanisms. Therefore, refined multidimensional models and linear discriminant functions are built to calculate the values of linear expansion with three distinguished classes considered. A performed analysis showed that values of linear expansion in the range of 1-6 % are formed depending on concentration of the additive and temperature. Then in the range of 6-10 % the process proceeds due to a synergistic effect of the joint influence of concentration of an additive and temperature

Predicting the permeability of the near-bottomhole zone during wave impact

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

Colloid Migration as a Reason for Porous Sandstone Permeability Degradation during Coreflooding

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