Evaluation of Sandstone Acidizing with High Strength HF Solutions

by
Maysam Pournik, M.S.E.

University of Texas at Austin, 2004
Supervisor: Alfred Daniel Hill

Acidizing of sandstone reservoirs results in uniform dissolution of formation, resulting in only near wellbore damage removal and limited permeability enhancement. In order to improve productivity of such reservoirs significantly, channels of high conductivity, called wormholes, like ones in carbonate formations must be generated. Wormholes can be created using an aggressive treatment of high concentration HF system at relatively high temperatures, as shown in several previous experimental studies in sandstone and also from theoretical studies on wormholing phenomena in carbonates.

From our theoretical work, we have been able to determine the parameters which have significant impact on the mode of acid attack. Wormholes can be created as long as dissolution is diffusion-limited with fast surface reaction rate that can dissolve most of the matrix material. While we were not able to create wormholes in our experiments, our results indicate that wormholes do not form below the threshold limit of reaction rate. There is a definite range of HF concentration and temperature below which wormholes cannot develop and propagate. Our simulator validated our experimental results.

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