Abstract

Acid treatment of carbonates is a common operation for production stimulation. A lot of codetergents for reaction rate decrease, for redistribution of acid placement in heterogeneous reservoirs and improvement of injection profile were proposed. These technologies are directed on stimulation improvement and are based on the mechanism of the carbonate acidizing which was investigated in the works [1, 2].

According to the investigated mechanism in some cases the flow and reaction of acid solution take place only in limited number of pore channels enormously increasing their radius and conductivity. This phenomenon was call wormhole formation. The existence of such channels raises well productivity significantly higher than in the case when acid flows through the whole porous media.

The research of Fogler and Fredd [2] resulted that wormhole formation depends on dimensionless Damkohler number. The general definition of Damkohler number is the ratio of reaction rate to the inflow rate to the reaction surface. So the value of the number depends on problem geometry. In the experiments on core plugs acidizing the formation of one channel occurs for number value 0.3 [3]. Increasing the Damkohler number (for instance by flow rate decrease) leads to the rise of the number of wormholes. The main trend is acidizing of all pores and front type chemical reaction with the whole carbonate consumption behind the front. In the inverse case (Damkohler number decrease) the sweep of pore channels by acid flow also rises but the asymptotical solution in this case is minimal impact of acid on rock (reaction rate is too small in compare with flow rate).

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