STUDY ON FLUID FLOW IN SANSTONE RESERVOIRS WITH MULTI-LEVEL FLOW MEDIUM
Typical sandstone reservoir has multiple layers in vertical directions, poor continuity in lateral directions and extreme heterogeneity of permeability. Sandstone reservoirs with high permeability, low permeability and extra-low permeability seepage areas that follow different percolation mechanism is called Multi-flow Medium Sandstone Reservoir. According to the value of permeability a geological model is divided into regions that follow different percolation mechanism. To be specific, fluid flow conforms to Darcy seepage in high permeability region, non-Darcy seepage with threshold pressure gradient at low permeability region and non-linear seepage in ultra-low permeability region. Seepage equation of Multi-flow medium sandstone reservoir is established with Darcy seepage, non-Darcy seepage flow and stress sensitivities coexisting, then equation is discretized and solved. Using the in-house reservoir numerical simulator it is shown that the simulation considering Darcy seepage, non-Darcy seepage and non-linear percolation causes smaller water flooding volume, lower sweep efficiency and worse reservoir development compared with commercial simulation reflecting Darcy merely. Because of threshold pressure gradient in the low and ultra-low permeability layers, oil is difficult to be displaced effectively. In the presence of stress sensitivity, pressure drops around well and inter-well during reservoir development result in decrease of permeability and increase of percolating resistance in the corresponding regions. Based on multi-flow medium sandstone reservoir that possess multiple fluid flow mechanisms, asynchronous injection-production takes advantage of reservoir stress sensitivity and imbibition between high and low permeability regions, and injected water channeling is controlled and sweep volume is enlarged, then effect of reservoir development is improved.