Summary For steamflooding processes, steam quality plays a crucial role because it affects enhanced oil recovery mechanisms and production performance. Many numerical simulations have been performed on the role of steam quality. However, few studies have evaluated the role of steam quality on steamflooding performance by experimental measurements because of the lack of a generalized experimental methodology to accurately generate and measure steam with different qualities under reservoir conditions. The objective of this study is to propose a generalized experimental methodology for investigating the role of steam quality on steamflooding performance. A steam quality controlling box was newly designed and fabricated to generate steam with different qualities, and its reliability was verified by a novel steam quality measurement system together with a developed theoretical method. Then, a series of experiments were conducted by our designed 1D and 2D sandpack models to evaluate the steamflooding performance under different steam qualities. The results showed that the developed methodology could accurately generate and measure steam with different steam qualities. The maximum errors between desired, measured, and calculated steam qualities were 4.39% under the experimental conditions in this study. The steam quality substantially affected the steamflooding performance. A higher steam quality led to a lower water cut, a lower maximum pressure difference between the inlet and outlet of the sandpack model, a lower water/oil ratio (WOR), a lower steam/oil ratio (SOR), a higher oil recovery, and a higher oil production rate. However, there is an optimal value of steam quality from the view of heat efficiency in this study. The oil recoveries of 2D steamflooding experiments increased from 36.30 to 45.02% when the steam quality increased from 0 to 0.8. However, the optimal steam quality of 0.6 had the maximum heat efficiency at 3.16×10−5 kJ−1. This research contributes to a better understanding of steam quality on steamflooding performance and also provides a generalized methodology for other steam injection processes.

Supercritical multi-thermal fluid (SCMTF) is a promising alternative to traditional thermal agents for deep heavy oil recovery. However, no 2-dimensional experimental investigation on SCMTF flooding has been conducted due to the limitations of existing apparatuses. Therefore, the primary objective of this study is to develop a novel assembly for investigating the performance of SCMTF flooding. Subsequently, the SCMTF chamber evolution is characterized using newly developed equipment, and enhanced oil recovery (EOR) mechanisms are proposed. Finally, the effects of the injection temperature, injection pressure, scN2/scCO2 mixture, and heavy oil viscosity on SCMTF are comprehensively studied. The results show that the SCMTF chamber displays an inverted trapezoidal shape with a uniform front. SCMTF flooding can enhance heavy oil recovery by 13.36% relative to steam flooding by sweep area expansion, oil mobility improvement, and miscible flooding. Increasing the injection temperature, injection pressure or scN2/scCO2 mixture to SCW molar ratio can facilitate the production of heavy oil, while using SCMTF in an extra-heavy oil cannot maximize the EOR effect of SCMTF. Notably, the high yield of coke produced at elevated temperatures may lead to potential formation damage.

Supercritical water (SCW) is a novel thermal agent that has been recently utilized for the production of heavy oil. However, a lack of knowledge about its recovery mechanisms limits the application of SCW. In this study, pyrolysis and sandpack flooding experiments were performed to investigate the mechanisms and viability of SCW flooding. Then an innovative simulation model was developed for SCW flooding. Finally, sensitivity studies on SCW flooding were conducted by the developed model. The results showed that SCW flooding yielded a 13.99% increase in oil recovery in comparison to steam flooding, indicating that SCW flooding is technically applicable to offshore heavy oil reservoirs. Heavy oil upgrading in SCW can suppress coke formation and plays an important role in oil recovery. A novel numerical model for SCW flooding was established based on a history match of experiments. The simulation results suggested that during SCW flooding, SCW could induce heavy oil upgrading to increase oil mobility, and long-term injection of SCW may cause the formation of coke deposits. Higher injection temperatures and pressures would benefit the production performance of SCW flooding. However, an unlimited increase in temperature would damage formations by significant coke deposits.

Different influencing factors in the process of polymer flooding have different degrees of influence on the development effect, so it is necessary to carry out the dynamic prediction of polymer flooding before implementing the development scheme. In this study, the reservoir model of C Block is established and the production performance is fitted. The fitted reservoir model is used to study the influence of polymer concentration, injection time, injection rate multiple and injection timing on the development effect of C Block. The results show that the cumulative oil production increases gradually with the increase of polymer concentration, and combined with the principle of economic development, there is an optimal polymer concentration in C Block, which is 0.15 wt%; With the increasing of injection time and injection rate multiple, the cumulative oil production and incremental oil production (compared with water flooding) show an increasing trend; For injection timing, the earlier polymer injection is more conducive to obtaining higher cumulative oil production and oil increment. The cumulative oil production under the optimal development scheme of C block is 23.8494×104 m3, which is 1.5042×104 m3 higher than that of water flooding.

The objective of this study was primarily directed to the development of experimental setups to investigate the potential of supercritical multithermal fluid (SCMTF) flooding processes. Then, the recovery mechanisms of SCMTF flooding were proposed for the first time. Finally, the impact of the injection temperature, injection pressure, injection rate, and supercritical nitrogen (scN(2)) and supercritical carbon dioxide (scCO(2)) mixture amount on the SCMTF flooding performance were systematically studied in this research. The results show that SCMTF flooding is a technically and economically viable recovery process for deep heavy oil reservoirs. Supercritical water (SCW) has a greater role than the scN(2) + scCO(2) mixture in SCMTF flooding. The most-efficient SCMTF flooding recovered an additional 32.24% of the original oil in place (OOIP) compared to steam flooding. The injection of SCMTF at a high temperature or pressure is beneficial for the production of heavy oil. However, the high yield of coke produced at a high temperature may lead to potential formation damage. Thus, using an intermediate amount of the scN(2) + scCO(2) mixture in SCMTF may lead to more efficient and economical performance.

As a novel thermal agent, supercritical multi-thermal fluid (SCMTF) has great potential to be used for heavy oil reservoirs. However, its viability and enhanced oil recovery (EOR) mechanisms have not been investigated. Therefore, a series of tests were conducted in a newly designed autoclave to compare crude oil pyrolysis in steam, supercritical water (SCW), SCW + supercritical nitrogen (scN(2)), SCW + supercritical carbon dioxide (scCO(2)) and SCMTF, and the viability of SCMTF was evaluated. Then, the possible mechanisms of pyrolysis in SCMTF were proposed. Finally, the effects of temperature, pressure, and the amount of SCMTF on pyrolysis in SCMTF were investigated. The results show that the SCMTF treatment of raw crude oil at 653 K and 23 MPa resulted in molecular weight, density and C15+ content reduction rates of 44.67%, 6.45% and 12.06%, respectively, and gave a gas yield of 7.91 wt % and an increase in the light oil fraction of 10.17 wt %. SCMTF is more effective than steam, SCW and SCW + scN(2) for upgrading heavy oil. In detail, SCW dominates the pyrolysis processes; scCO(2) accelerates dealkylation, and increases oil mobility by dissolution and light hydrocarbons extraction; and scN(2) can maintain reservoir pressure and form a gas-cap, which reduces heat loss. Increases in scCO(2) fraction, temperature, pressure and the amount of SCMTF can enhance the heavy oil upgrading. However, pyrolysis at a high temperature is adverse to light oil production (the oil product yield was merely 67.10% at 683 K) due to undesirably high gas and coke yields of 13.32% and 19.58%, respectively.