Determination of critical alkalinity (pH) in Fahliyan carbonate reservoir using a new methodology

Abstract

Formation damage is a great concern in reservoir management and can potentially occur due to exposure of formation to alkaline fluids. Exceeding pH over a critical pH may result in an in situ release of fine particles and therefore can cause pore plugging. In this study, a series of core-flooding experiments was carried out to determine the critical pH of alkaline fluids flooding through core samples of Fahliyan carbonate formation. Alkaline fluids with different pH were injected into the core samples and the alkaline sensitivity of the carbonate formation was measured in both qualitative and quantitative forms. The applied approach provides an accurate determination of the degree of formation damage at a base pH (pH = 7) following successive changes in the fluid alkalinity. In addition, the pH values corresponding to different degrees of formation damage, determined qualitatively in other works, are calculated precisely in this paper. The flooded cores showed different response when exposed to fluids with different alkalinity while the degree of induced formation damage varied from ‘negligible’ to ‘severe’ which were, in some cases, noticeable and often irreversible. A polynomial relationship between the fluid alkalinity and the corresponding degree of formation damage was proposed for core no.3, which is compared with the conventional methods (Renpu method) underestimating the degree of formation damage (Dk) compared to the modified approach introduced in this paper.