Multi-thermal fluid assisted gravity drainage process: A new improved-oil-recovery technique for thick heavy oil reservoir

•The superiority of multi-thermal fluid is experimentally investigated from PVT performance and displacing characteristics.•A new IOR technique, Multi-thermal Fluid Assisted Gravity Drainage (MFAGD) process is proposed.•Two 3D gravity-drainage experiments (SAGD, SAGD-to-MFAGD) are performed.•The EOR mechanisms of multi-thermal fluid in heavy oil reservoirs are analyzed.

Multi-thermal fluid is a new heat-carrier proposed in decades. This paper introduces multi-thermal fluid into the thermal recovery process of thick heavy oil reservoir (THOR). First, using the method of physical simulation, the superiority of multi-thermal fluid is investigated from the Pressure–Volume–Temperature (PVT) performance and displacing characteristics. Thereafter, based on multi-thermal fluid injection technology and steam-assisted-gravity-drainage (SAGD) theory, a new Improved-Oil-Recovery technique for THORs, Multi-thermal Fluid Assisted Gravity Drainage (MFAGD) technique is proposed in this paper. Applying the dimensionless scaling criterion of gravity-drainage process, two 3D gravity-drainage experiments (SAGD, SAGD-to-MFAGD) are conducted. Thus, the enhanced-oil-recovery (EOR) mechanisms of multi-thermal fluid in heavy oil reservoirs are analyzed, and the thermal recovery performance of MFAGD process is discussed. Results indicate that compared with SAGD process, MFAGD process has a higher recovery rate, and it could further improve the gravity-drainage effect in THOR. Besides the conventional operation of SAGD, the EOR mechanisms of MFAGD technique also include heat insulation, energy recovery, gas dissolution and auxiliary cleanup of non-condensable gas. This method technologically supports the effective and efficient development of THORs.