A Simulation Study on Solvent-Aided Process using C3 and C4 in Clearwater Oil-Sand Formation

Abstract

Solvent-aided processes (SAP) have been considered to enhance the energy efficiency of Steam Assisted Gravity Drainage (SAGD) process for hydrocarbon recovery from oil-sand formations. We performed numerical simulations to investigate how solvent type and concentration affect the performance of SAP. First, we created simulation models in which light solvents are co-injected with steam into a developed steam chamber in Clearwater oil-sand Formation. Second, we investigated the phase behaviour of steam-solvent-bitumen and its effects on bitumen viscosity at steam-bitumen interface. Third, we investigated the effects of solvent concentration on production performance of SAP.The results show three main stages in bitumen production profile during SAP. Oil rate reaches two peaks (one during the first stage, and one during the second stage), then drops and stabilizes during the third stage. During the first stage, C4 condensation near the chamber edge leads to dilution and drainage of the heated bitumen. During the second stage, the steam chamber grows more laterally. During the third stage, as water accumulates at the bottom of the chamber, steam chamber volume decreases. In addition, contact area between the condensed solvent and bitumen reduces. Therefore, oil rate stabilizes even though solvent is co-injected with steam during this stage due to the adverse effect of water accumulation near the production well. Compared with C4-steam co-injection process, C3-steam co-injection leads to higher bitumen viscosity near the chamber edge due to 1) less C3 solubility than C4 in the oil phase and 2) lower chamber temperature in the C3-steam co-injection. Maximum-performance scenarios for C3-, and C4-steam co-injections are co-injecting C3 with steam at 2% mol C3 and co-injecting C4 with steam at 3% mol C4. These scenarios of C3- and C4-steam co-injections lead to 1.5% and 5% increase in SAGD ultimate bitumen recovery factor, respectively. C3- and C4-steam co-injections with maximum-performance scenarios reduce SAGD cummulative steam oil ratio (CSOR) by 31.5% and 29%, respectively.