Creation of high-conductive filtration channels in core samples when simulating acid exposure at a filtering unit

Background. Hydrochloric acid treatment is currently one of the main methods used for recovering and improving the reservoir properties of bottom-hole formation zones. In the process of acid treatment, during the reaction of the acid composition and the rock, highly conductive filtration channels are formed. The structure and shape of such channels characterise the treatment efficiency. As a result, much research attention is currently paid to predicting the formation of filtration channels and changes in the filtration characteristics of reservoirs with different properties and types of pore space.Aim. To study the factors that directly affect the formation of dissolution channels in core samples when simulating hydrochloric acid treatment of the bottom-hole zone of carbonate reservoirs on a filtration unit. The main objectives are to determine the significance of these factors and to establish dependencies reflecting their effect on the efficiency of technologies aimed at stimulating oil inflow.Materials and methods. We used the results of filtration and X-ray tomographic studies on core samples taken from the scientific base of the “Geology and Development of Oil and Gas Fields” Scientific and Educational Centre. The collection of rock samples is represented by various deposits confined to the oil and gas complexes of the Perm Territory.Results. The conducted analysis allowed us to identify the effect of various factors on the formation of highly conductive filtration channels during acid treatment. These factors were found to include the lithological and mineralogical composition and initial filtration parameters of core samples, as well as the type of pore structure. Dependences that characterise the efficiency of acid treatment were determined.Conclusions. The obtained results can be used when developing measures for the intensification of oil production, taking into account the revealed factors.

Mathematical modelling of carbonate reservoir dissolution and prediction of the controlled hydrochloric acid treatment efficiency

The article presents the theoretical studies results of hydrochloric acid compositions filtration in carbonate collectors porous media saturated with two-phase formation liquid. Solution of filtration problem in the process of carbonate rock leaching with possible regulation of process by hydrocarbon solvents is considered. Numerical algorithm of acid effect on oil-saturated formation is proposed and tested, which allows to determine the following parameters of filtration flow: concentration of hydrochloric acid, distribution of water saturation, pressure and other parameters. A mathematical model of the carbonate collector dissolution process using composite solvents has been developed, which allows predicting technological indicators of acid impact efficiency.

Facile Synthesis of Flower-Like TiO2-Based Composite for Adsorption–Photocatalytic Degradation of High-Chroma Methylene Blue

A flower-like TiO2-based composite (denoted as Zn-Ti-6) was prepared using a flower-like zinc oxide template for adsorption–photocatalytic degradation of high-chroma methylene blue. The reaction took place in an alkaline environment following hydrochloric acid treatment to remove the template and form TiO2-based composite. Sodium hydroxide played both roles of morphology-directing agent and reactive etchant. The possible mechanism for the formation of flower-like Zn-Ti-6 was proposed. The adsorption and photocatalytic degradation behavior of Zn-Ti-6 on methylene blue (MB) removal was also investigated. The results revealed that Zn-Ti-6 showed better adsorption and photocatalytic degradation performance than TiO2 nanoparticles owing to its much larger specific surface area, more abundant hydroxyls, and lower photoluminescence intensity. The adsorption and photocatalytic degradation data of Zn-Ti-6 were well fitted to the pseudo-second-order and pseudo-first-order kinetics models, respectively. The excellent adsorption performance of Zn-Ti-6 is largely beneficial to the subsequent photocatalytic degradation performance for high-chroma wastewater treatment. Overall, this study contributes a facile fabrication strategy for flower-like TiO2-based composite to achieve the adsorption–photocatalytic degradation of high-chroma wastewater.

Analysis of the Acid Compositions Application in High-Temperature Carbonate Reservoirs

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.

Theoretical features of improving the oil recovery efficiency from carbonate reservoirs in the Volga-Ural province

Currently, the share of hard-to-recover oil reserves confined to carbonate reservoirs is more than 20% of the Volga-Urals hydrocarbon reserves. The use of traditional acid stimulation in conditions of a complex structure of carbonate reservoirs and low reservoir pressure is ineffective. In order to increase the efficiency of hydrochloric acid treatment, theoretical and experimental studies have been carried out aimed at increasing the efficiency of the work being carried out to stimulate the inflow to production wells that operate carbonate reservoirs. Filtration of the acid solution into low-permeability intervals of the carbonate reservoir involves the use of reverse counter-current capillary impregnation mechanisms. Analytical research methods made it possible to determine that the activation of the impregnation processes is carried out under conditions of nonstationarity of the pressure parameters of the reservoir system. Numerical modeling of the exposure process allowed to optimize the exposure parameters.

Hydrochloric acid treatment of the well

This article is about salt chemical treatment and hot acid treatment of wells. In this case, research has covered different points of theoretical and methodological the hydrochloric acid treatment of the well. Finally, research has pinpointed on various views of outcomes and shortcomings at all.