Perm Journal of Petroleum and Mining Engineering

The adsorption activity of soils largely depends on their composition and properties and, first of all, on the specific surface area and energy potential of clay particles. For the formation of "specified" properties, including adsorption, various methods of clay activation have been developed: thermal, ultraviolet, ultrasonic, mechanical, acidic, alkaline. However, despite the published data, the issues of the influence of heat treatment on the formation of the clays properties, including adsorption ones, have not been sufficiently studied. In this regard, an assessment was made of the of clays thermal activation effect on their adsorption activity for the methylene blue dye. Experimental and theoretical studies have shown that the change in the adsorption activity of clays is associated with the degree of their heat treatment. When clays are treated with temperatures up to 200° C, energy centers on the surface of structural elements are activated, which leads to an increase in the clays adsorption in terms of methylene blue by 12-24%; with an increase in the processing temperature of clays to 450-960° С, the processes of their (clays) structural transformation change, which reduces the adsorption activity of clays by 11-16 times. In addition, the influence of the clays saturation degree with water vapor on their adsorption activity has been established. During the heat treatment of clays and their partial saturation with water vapor, water molecules occupy part of the energy centers on the surface of the particles; therefore, the particles have a sufficient energy potential, which is realized in the form of high values of their adsorption to methylene blue. During the clays thermal treatment and their complete saturation with water vapor, the charges on the surface of the particles are mostly compensated by water molecules. Water molecules, entering the inter-package space, compensate charges on the surface of the packages and minerals, which are realized in the form of clay swelling processes. Swelling processes lead to an increase in the size of structural elements, which manifests itself in the form of a decrease in the specific surface of clays. Therefore, clays completely saturated with water vapor are less active adsorption than clays partially saturated with water vapor.

Recently, it is necessary to note the presence of negative dynamics in the deterioration of the reserves structure for newly discovered fields, and most of the them are classified as hard-to-recover, confined to deposits with a complex geological structure, low permeability, high oil viscosity, complicated by the presence of faults, active bottom waters and gas caps. Hard-to-recover reserves are drilled with horizontal wells. This is primarily because horizontal wells make it possible to multiply the area of fluid filtration due to the increase in the drainage area, due to the extensive contact of the horizontal well section with the rock, allowing to increase the well flow rate many times over. Summarizing the above, horizontal wells are used to develop fields with the following parameters: fields with a thin oil-saturated rim (up to 15 m), with a gas cap and bottom water; fields of heavy oil, with a viscosity of more than 30 mPa·s; fields with low reservoir permeability (less than 0.002 μm2). Under these conditions, linear Darcy’s law cannot describe fluid filtration. Under the conditions of high-viscosity oil and low-permeability reservoir existence, a certain initial pressure gradient is determined, due to the rheological properties of the filtering fluid and high values of the surface friction coefficient. Under conditions of a thin oil rim and an increased gas factor, the limiting filtration rates due to the dissolved gas regime are observed, and a nonlinear law describes the fluid inflow. One of the main parameters in the preparation of the technical and economic assessment of the reservoir is the flow rate of each individual horizontal well. Analytical methods for calculating the horizontal well flow rate show a high error. It is proposed to take a fresh look at the problem of determining the predicted flow rate of a horizontal well, using well-known approaches for solving this issue. It is rather difficult to reliably predict the parameters of reservoir operation: the horizontal wells productivity obtained with the help of modern hydrodynamic stimulators turns out to be unreliable, which leads to the formation of an insufficiently rational development system. And the arising complications during operation in field conditions have to be eliminated due to significant volumes of material and labor resources. Thus, the development of methods that contribute to obtaining a reliable calculation of production is an urgent task for the oil industry.

The use of hydrochloric acid treatment goes back a century. For the first time the company “Ohio Oil” applied acid for formation stimulation in 1895, and the patent for acidizing limestone was obtained by the company "Standard Oil". However, with a significant increase in production volumes, it turned out that acid solutions caused very strong corrosion of downhole equipment. Therefore, the hydrochloric acid treatment method had not been used for 30 years. The discovery by John Grib of “Dow Chemical” in 1931 - slowing down the effect of hydrochloric acid on the metal with arsenic - made it possible to return to this method, and three years later “Halliburton Oil Well Cementing” began to practice acidizing on an industrial scale. As the analysis of the field material has shown, there are many technologies with the use of modified acids intended for acidizing, which are characterized by a high degree of success. Nevertheless, according to the estimates of different authors, the treatments success varies in the range from 60 to 80%, and for repeated treatments - less than 50 %. The urgency degree of the problems associated with acid treatment of the bottomhole formation zone and the tendencies of its development was investigated. Analysis of patent information according to the International Patent Classification for 17 years (from 1997 to 2013 inclusive) for Russian patents and for 15 years (from 1999 to 2013 inclusive) - for American ones showed stable activity of Russian organizations, while foreign organizations showed in this respect a significant growth of interests and achievements. Foreign experts mainly investigated the modeling of acid treatment [6-11], while Russian specialists were more inclined towards service support of acid treatment. It was revealed that there were no methods for calculating the risks of falling out of heavy oil components during acid treatment, depending on the geological and physical conditions of the target.

An analysis of the formation of asphaltene resin paraffin deposits is presented, criteria for assigning wells to subgroups of the complications type are considered, and a classification of complications in oil production is proposed. Oil is a complex and varied mixture of various hydrocarbons, both light and heavy, in thermodynamic equilibrium under reservoir conditions. In some fields, oil production is not accompanied by the formation of asphaltene resin paraffin deposits on the downhole pumping equipment, while in others it is complicated by them. Methods of preventing the deposition of asphaltene resin paraffin deposits and methods of dealing with them are considered, the research work done to substantiate the use of chemical reagents to prevent the formation of complications in oil-producing wells is presented, the minimum measures for subgroups of the proposed classification, complicated by asphaltene resin paraffin deposits of the fund, are presented. The methods for determining the effectiveness of the asphaltene resin paraffin deposits inhibitors, developed in the PermNIPIneft branch of LLC LUKOIL-Engineering, were briefly presented, on the basis of which the studies were carried out. The results of studies on the selection of reagents and determination of their effectiveness for the production well stock complicated by asphaltene resin paraffin deposits were considered. It was found that during wells operation where the physicochemical properties changed, the effectiveness of the inhibitor significantly decreased and did not reach the efficiency criterion of 75%. So, in oil production it is necessary to periodically, at least once every three years, check the effectiveness of the selected reagents, as well as analyze changes in such parameters of the processed object as: change in the physicochemical properties of the fluid; geological and technical measures at the well; significant increase, decrease in production; involvement or isolation of interlayers, production facilities; changes in reservoir, bottomhole pressure during operation. Approaches for wells are proposed: where, as a result of research, the criterion of the effectiveness of chemical reagents has not been achieved, it is necessary to select other methods to avoid the complication.