Fundamental principles of matrix acidification in carbonate reservoirs during oil production

The acid treatment process is one of the oldest methods used for well intensification. The success of this operation, along with some others, has opened the door to the use of matrix acid treatment, which can be adapted by various oil producing companies. Matrix acid treatment makes it possible to improve or restore the permeability of the area near the borehole without hydraulic fracturing and is most useful in cases where it is necessary to maintain the boundaries of shale fracturing and natural flow in order to minimize gas and water production to obtain a high percentage of oil production without increasing gas or water production. An increase in permeability will reduce the pressure drop associated with fluid injection or extraction by expanding the pore neck or eliminating damage to the formation. The purpose of acidification of the matrix is to achieve radial penetration of acid into the formation by expanding the pore spaces or dissolving damaging particles from the bottomhole zones. The article provides an overview of the most common mineral and organic acids used in oilfield practice, as well as industrially developed acid formulations. The features of their use depending on the lithology of the formation and thermobaric conditions are described. A typical five-stage process of matrix acid treatment of a carbonate reservoir is described in detail, including borehole cleaning, pre-rinsing, basic acid treatment (with possible application of extraction methods), flushing and displacement. The mechanism of acid-rock interaction at the molecular level, including the transfer of hydrogen ions, their reaction with calcite and dolomite, as well as the diffusion of reaction products, is considered. The key role of temperature in regulating the rate of these processes is noted.