Impact of reservoir heterogeneity on Steam Assisted Gravity Drainage in heavy oil fractured reservoirs

摘要

Despite successful experiences of Steam Assisted Gravity Drainage (S AGD) in sandstone and some studies of this process in fractured reservoirs, the impact of heterogeneity and its relative solutions have not been assessed yet. In this paper, SAGD in fractured reservoirs was studied and the impact of reservoir heterogeneity of fracture permeability, fracture spacing and matrix permeability and solutions to overcome negative impacts were investigated. In contrast to sandstone, it is found that due to the drainage of fracture initial mobile water, steam is injected into reservoir in large amount in early time resulting in fast rising of steam while the lateral expansion of steam is not considerable. Higher fracture permeability at top part of the reservoir showed lower oil recovery than the reversed condition. The impacts of matrix permeability and fracture spacing were combined and expressed in a term H_m/K_m (H_m: matrix height, K_m: matrix permeability). It was observed that higher value of this term for the top part of the reservoir deteriorates oil recovery more than the reversed condition. The negative impact of heterogeneity can be overcome by locating injector in more fracture permeable zone or the layer having lower quantity of the mentioned term.