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Mud acid treatment is a conventional chemical enhanced oil recovery method commonly used in sandstone reservoirs. The paper presents results of analysis of field data, review of domestic and foreign literature, and patent research on chemistry and technologies of bottomhole zone mud acid treatments in sandstone reservoirs. It was found out that application of hydrofluoric acid for treatment of sandstones containing clayey and carbonate rocks initiates adverse physical and chemical processes in situ resulting in formation of reservoir-damaging compounds in the near-wellbore zone. Besides, HF acid is characterized by increased toxicity and corrosivity. The solution of the problem is seen in improvement of efficiency of mud acid treatments through improved design of HF acid-free chemical compositions and advanced injection technologies. The first stage of the project involved lithological analysis to understand and to describe the mineral composition of the Tulskian-Bobrikovskian core samples. More than 50 core samples (sandstones, siltstones, mudstones) from the Ersubaikinskoye, Arkhangelskoye, Vostochno-Ekaterinovskoye, Tyugeevskoye, Shegurchinskoye have been analyzed, including radiographic and micrographic studies of thin sections. The second stage involved morphological and genetic analysis of clayey minerals to understand the possible effect on the reservoir properties following mud acid treatments. Studies using X-raying, optical and scanning electron microscopes provided quality visualization of pore space, as well as main quantitative core parameters for future model studies and chemical treatment control: volume of pore space, total volume of a core sample, pore space volume to total core sample volume ratio, number of pores in the core sample. The first results of physical modeling studies demonstrated the necessity and the importance of targeted stimulation of various lithological types of reservoirs, even of the same formation. |
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