Fractal Description of Pore Structures of Low Permeability Oil Reservoirs and its Relationship with Gemini Surfactant Flooding

Abstract Gemini surfactant flooding is a promising technique to enhance oil recovery from medium-high permeability oil reservoirs. The screening of the gemini surfactants are mainly based on their capability of lowering the surface tension between oil and water. However, gemini surfactants with high capability of lowering the surface tension do not necessarily enhance oil recovery from low permeability oil reservoirs. Based on fractal method and the mercury injection curve data, the fractal dimensions of the pore structures of low permeability oil reservoirs are different from those of medium-high permeability oil reservoirs. Based on the fractal dimensions of molecular fragments, the fractal dimensions of gemini surfactants are in relation to the fractal dimensions of the pore structures of low permeability oil reservoirs. Based on the fractal dimensions of the pore structures of low permeability oil reservoir Z and molecular fragments, gemini surfactant D is designed and applied in developing the reservoir. Gemini surfactant D enhanced oil recovery 5% more than conventional gemini surfactants. The fractal dimensions of the pore structures of medium-high permeability oil reservoirs range from 2 to 3. The fractal dimensions of the pore structures of low permeability oil reservoir Z are less than 2. The fractal dimension of the spacer group should match with fractal dimensions of the pore structures. The gemini surfactants are absorbed more onto the rock surface as the spacer groups of the gemini surfactants are less complicated than the rock surface. Fractal dimension is supplementary to the parameters (permeability and porosity) that are used to estimate low permeability oil reservoirs. Low permeability oil reservoirs which were not able to be developed are able to be developed. This helps more and more low quality reserves be turned into producing reserves.