Study of the effectiveness of restoring the permeability of near-borehole zones

Abstract

When drilling into a reservoir zone, the main goal is to reach it without damaging the pore space. Damage to the pores can happen because of the drilling mud. Drilling mud, especially when it has solid particles and clay, can block the pores near the wellbore — this is called formation damage. To avoid this, drilling fluids often contain bridging agents, usually finely ground carbonate rocks. These small particles move into the pore spaces of the reservoir zone. While drilling through the productive layer, they protect it from the further invasion of drilling mud and its filtrate. After drilling is finished, the area where the bridging agents entered the formation is cleaned with hydrochloric acid (HCl). The acid reacts with the carbonate (CaCO₃), dissolving the blocking material. This process restores the permeability of the reservoir zone and allows hydrocarbons to flow freely into the well. The aim of this work is to explain the theoretical background of this topic and to perform laboratory tests that confirm the effectiveness of this process.