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Core Flood Analysis of Acid Stimulation in Carbonates: Towards Effective Diversion and Water Mitigation
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, IPTC 2014: International Petroleum Technology Conference, Jan 2014, cp-395-00154
Abstract
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 occuring. 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.