Commingled Injection and Separate-layer Production to Improve the Development Performance of Gas Flooding in Multi-layer Oil Reservoirs
Continental low-permeability sandstone oil reservoirs generally have multiple layers and strong interlayer heterogeneity, which results in uneven sweep between layers and low oil recovery by gas flooding in the mode of commingled injection and commingled production. Conventional solutions such as separate-layer gas injection are immature and face a lot of engineering problems. This paper proposes a commingled gas injection but separate-layer oil production scheme to address the problem of interference between layers. According to the typical geological properties, reservoir properties, well pattern and well spacing parameters in Daqingzijing Oilfield in Jilin, a numerical CO2 flooding model is established, and a set of method and process for designing the suitable production rate of each layer at the side of production well is developed. The results indicate that regarding the multi-layer heterogeneous oil reservoirs, the proposed commingled injection and separate-layer production scheme can effectively promote uniform displacement between layers and delay gas breakthrough. It can not only enlarge CO2 swept volume in low-permeability layers, but also promote miscibility of CO2 and oil in high-permeability layers, thus effectively improving the overall oil recovery.