Abstract: The adsorption of crude oil surfactant component in the wall of pores and throats forms a boundary layer which has more influence on low permeability reservoirs than that on high permeability reservoirs. It is this boundary layer that causes start-up pressure gradient in low permeability reservoirs to be much higher than that in middle-high permeability reservoirs. In this paper, the formation of boundary layer and its influence factors are analyzed, and then a pore scale network model is developed for percolation simulation, finding out a flow curve between pressure gradient and flow velocity, by which determining the start-up pressure gradient. This method studies the start-up pressure gradient by considering the effect of boundary layer directly for the first time. In addition, it extends the usage of pore scale network model to low permeability reservoirs.

Key words: network, model, percolation, low permeability reservoir, start-up pressure