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Extended Abstract Introduction: It is well established that acid stimulation in carbonates can enhance the productivity of oil and gas wells. As carbonate porous media are highly reactive in contact with acidic solutions, when acid is injected into carbonate reservoirs, the near wellbore region is subject to chemical dissolution. This is a reactive transport phenomenon, as acid is flowing and transported through a porous media. Coupled changes of the fluid and rock properties are taking place. Changes in chemical concentrations of the in situ fluids, the surface area, the permeability and porosity are also occurring. In this context, many studies have experimentally and numerically investigated carbonate acidizing. It has been shown that different dissolution regimes can be observed based on two main parameters, basically, the injection flow rate and the acid content. Wormholing i.e. a non uniform dissolution which is characterized by the creation of a conductive pathway along the porous media, is therefore observed for relatively high flow rates and low pH (high acid content). It also has been shown that for a certain pore structure, optimum injection rates, where the minimum acid volume leads to the highest permeability increase, (optimum wormholing) exist. Therefore, in field applications during acid stimulation jobs, the acid is injected at relatively high pumping rates in order to achieve an efficient zonal coverage and sweeping efficiency. Today, acid stimulation is widely used for newly drilled wells or wells that are experienced in production decline. Context: It has been observed that acid stimulation of carbonate oil and gas wells, especially in mature carbonate fields, can be inefficient and might sometimes lead to negative outcomes. Targeted low permeability regions can be kept untreated and water production might arise after the acid injection. These negative results are often explained by the presence of a high permeability matrix contrast or the presence of active fracture networks in the reservoir. In such configurations, the acid enters the highest permeability matrix regions or flows through the fracture networks and might connect to a new water pathway. A large number of investigations have considered chemical or mechanical diversion techniques that allow the acid to stimulate a low permeability zone in the presence of a permeability contrast. In addition, a series of studies have considered reducing water production through water shutoff chemical products. Although efforts have been made towards fluid formulations, only a few studies have considered the experimental validation of diversion and water mitigation in heteregenous carbonates. In this paper, we experimentally revisit improved acid stimulation techniques in the presence of watered and permeability-contrasted carbonates. |