THE EFFECT OF MATRIX ACIDIZING ON THE COMPRESSIVE STRENGTH OF SANDSTONE FORMATION

This paper discusses the effect of matrix acidizing on the compressive strength of a sandstone formation. The laboratory works involved two main systems, namely the acidizingpermeability apparatus and servo hydraulic equipment. The mud acid with 1-9% HF concentrations was used to treat the damaged Berea sandstone core samples using different injection pressures ranging from 30 psi (206 KN/m²) to 660 psi (4550 KN/m²) at room temperature. The Berea sandstone core sample was initially damaged using drilling mud before the matrix acidizing took place. After the acidizing process, the value of improved permeability of the acidized core sample was compared with the damaged permeability, which was measured using the acidizing-permeability apparatus. The compressive strength of sandstone formation after the acidizing process was also evaluated using the Servo Hydraulic Equipment. The experimental results revealed that acidizing could improve the permeability of the damaged core sample but would affect the compressive strength of the core sample, especially when using 9% HF-12% HCl. The volume of mud acid required to achieve ARC 1.0 reduces when injection pressure increases, which should be greater than 30 psi (206 KN/m²) in order to achieve ARC greater than 1.0. It was also noted that higher injection pressure would reduce the overall effectiveness of the acid treatment due to insufficient reaction time.