Pore network modeling of carbonate acidization

Abstract

Over half of the world's hydrocarbon reserves are found in carbonates. Acid injection is a cost effective way to enhance productivity in carbonates by reducing the near-wellbore skin. Ideally, injected acid creates highly permeable channels around the wellbore, known as wormholes. The successful formation of these wormholes depends on acid type, injection rate, and reservoir properties. Improper treatment design results in sub-optimal acid placement with negligible permeability increase. Previous attempts to accurately capture the wormholing process using a pore-scale network model have encountered many difficulties. We present a modern pore network model of carbonate acidization using networks extracted from CT scans of carbonate cores. A mass transfer coefficient and pore merging criterion are developed using finite element simulations in COMSOL that both greatly improve network physics. While there are many weaknesses to the pore network modeling approach, the optimal Damkohler number for our networks closely matches experimental data.