Surfactant has important guiding significance for improving crude oil recovery

2022-08-24 16:17:33

Optimization of surfactant system suitable for low permeability reservoirs has important guiding significance for improving oil recovery.   

The low permeability reservoir has low permeability, small low pore throat and low porosity. In the long-term water drive process, the permeability of the reservoir decreases again due to the hydration expansion of clay particles, and the injection pressure increases and it is difficult to inject. Therefore, higher requirements are put forward for surfactant flooding system in low permeability reservoirs. The surfactant agent is selected according to the conditions of the oil field to comprehensively evaluate the interfacial activity, wettability, anti swelling, oil washing efficiency and oil displacement efficiency of the system, and to select a high-efficiency surfactant system for oil displacement in low permeability reservoirs. In order to increase the number of displacement fluid capillary, change the reservoir wettability, reduce the start-up pressure of oil droplets, make the oil film easier to peel off from the rock surface, slow down the reservoir damage caused by the dispersion and migration of clay particles, and improve the oil recovery of low permeability reservoirs.   

The characteristics of low permeability reservoirs include the following aspects:

1) Many faults and complex structures, small oil-bearing area, many layers, large thickness, many faults and complex structures are the basic characteristics of this type of oil field. Due to many faults and compactness, the reservoir is often divided into isolated small fault block oil fields. The oil-bearing area is relatively small, but the thickness of multiple layers varies little, from several meters to tens of meters, even hundreds of meters.     

2) The physical properties of the reservoir change greatly, with small pores, large specific surface area and low permeability. The small pores and micro micro throats dominated by low permeability reservoirs have an average throat diameter of 26-43 µ m, a median pore throat radius of 0.1-2.0m and a specific surface area of 2-20m2 / g. The pore throat of the reservoir is small and the specific surface area is large, which directly forms the result of low permeability and is the fundamental reason for a series of production and production of low permeability reservoirs.  

3) The percolation characteristics do not follow Darcy's law. Due to small pores, large specific surface area and oil layer boundary thickness, strong Jamin effect and surface molecular force, the percolation characteristics of low permeability reservoirs do not obey Darcy's law, and the non Darcy percolation characteristics are obvious. The lower the permeability, the larger the starting pressure gradient.       

4) The elastic energy is small, and the low permeability reservoir has low flow resistance due to poor reservoir connectivity. Generally, the edge and bottom water are not active, and the elastic energy is very small. Except for a small number of abnormally high pressure reservoirs, the recovery rate in elastic stage is only 1% to 3%.