Abstract:
Cyclic steam injection (CSI) is a thermal recovery technique performed by injecting periodically heated steam into heavy oil reservoir. Oil viscosity is substantially reduced by means of heat transferred from steam. Together with gas pressurization, oil recovery is greatly improved. Effects of reservoir heterogeneity together with reservoir parameters are evaluated prior to field implementation. Judging of the best operating parameters is based on oil recovery factor and energy consumption. Steam quality of 1.0 together with soaking period of 6 days is chosen as the best condition. Results show that reservoir heterogeneity in terms of Lorenz coefficient value slightly affects CSI process. Reservoir model with Lorenz coefficient value of 0.328 which is moderate heterogeneous model obtains benefits from well-distribution of permeability and good steam propagation. High oil recovery factor is obtained from early and later periods and low energy consumption is achieved. Higher vertical permeability is more favorable for CSI process. Better propagation of steam in upper layers and percolation of hot condensed water due to gravity results in high oil recovery factor. Higher portion of structural shale reduces performance of CSI process due to reduction of thermal conductivity of rock and hence, this condition is not favorable. Lower value of Corey’s exponent favors steam propagation in top layers due to high effective permeability of fluids. Smaller irreducible water at reservoir temperature results in higher initial oil saturation. Therefore, higher portion of oil receives heat from steam, resulting in high oil recovery. Smaller residual oil at elevated temperature is favorable since oil can be maximally recovered. Coarsening upward permeability sequence leads to well development of steam chamber on top of reservoir that consequently causes percolation of hot condensed water to lower layers, whereas steam tends to expand in middle layers in fining upward sequence.
