In order to improve the waterflooding efficiency, surfactants and polymers are added to the water; this process is called surfactant–polymer (SP) flooding. One of the problems for this process is high adsorption of surfactants to the rock surface and specially to carbonate rock surfaces. The focus of this work is: to quantify experimentally the adsorption of anionic surfactants to carbonate rock surfaces, obtain a qualitative understanding of the mechanisms at play and identify suitable adsorption inhibitors.

The main outcomes of the work are: the adsorption of the surfactants used can be around three times higher (mg per g of rock) on calcite than on sandstone and dolomite. Higher concentrations of divalent ions lead to higher adsorption, and the adsorption also depends on the monovalent ion concentration. Several adsorption inhibitors are identified that can reduce the adsorption substantially, of which polyacrylate showed the most significant reduction. The divalent ions are thought to form a bridge between the anionic surfactants and the charged rock surfaces. The adsorption inhibitors capture the divalent ions, reducing their concentration in solution and, consequently, the adsorption of surfactants. More work is needed on the effectiveness of this concept at higher salinities before a first-pass technical and economic evaluation on the use of adsorption reducing agents on a field-scale can be performed.

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