Heavy oil extraction via thermal enhanced oil recovery (EOR) methods is a challenging task due to low mobility of oil at reservoir conditions and high petroleum processing cost due to high impurity content of heavy oils. This task becomes more difficult with the decrease in oil prices. Hence, any effort to decrease the recovery or refinery cost of heavy oil production can make the extraction of these unconventional resources more feasible.
Existing screening criteria tables are still in use to find the optimum thermal EOR methods to recover heavy oil reservoirs. However, since those tables ignore the role of oil and rock compositions in the success and failure of oil recovery through thermal methods, generally the thermal EOR response is different than expected. This study aims to extend existing screening criteria tables for thermal EOR methods by including the impact of oil and rock composition and investigates the produced oil quality originated from different EOR techniques. First, lab-scale steam assisted gravity drainage, in-situ combustion (ISC), steam injection, hot-water injection, and steam/solvent injection experiments were conducted on two different heavy oil samples. The success of each EOR process, the impact of oil type and reservoir rock were interpreted based on the variations between initial and the produced oil viscosity, density, and SARA (Saturates, Aromatics, Resins, and Asphaltenes) fraction content.
Hydrocarbon composition of initial and produced oil samples was compared using Gas Chromatography-Mass Spectrometry (GC-MS). The differences in the molecular signatures were analyzed by a Fourier Transform Infrared (FTIR) Spectroscopy on initial and produced oil samples. GCMS analyses of initial oil samples indicated the biodegradation of the two crude oils were different and they showed high (low lighter component content) and slight (high lighter component content) biodegradation. In terms of produced oil quality, highly biodegraded oil sample responded to ISC better than the slightly biodegraded oil sample. Steam processes upgraded the highly biodegraded oil for the reservoir without clay.
Thermal EOR methods are costly especially at the current price environment. Furthermore, because of the differences in the response of different thermal EOR methods to different reservoirs due to compositional variations in reservoir oil and rock, the thermal EOR methods are not widely applied. Our study is a step taken to improve the existing screening criteria tables to determine the successful thermal EOR candidates through inclusion of oil and rock compositions.