## 5 Conclusions  
In this work, a numerical investigation was performed to evaluate the bottom-up assisted pressure drive process for bitumen resources. Underlying mechanisms were examined using the simulation model with similar properties to the typical Athabasca reservoir, considering shale barriers.  
In the bottom-up assisted pressure drive, a flat steam chamber was developed from the bottom of the reservoir in the early stage of the process and grew upward with the injection of steam. The large volume of the steam chamber and the huge contact area between the steam and bitumen contributed to a high oil production rate. The presence of shale barriers affected steam chamber development negatively in both processes. The effect of shale barriers on bottom-up assisted pressure drive was less, indicating one advantage of this novel process over SAGD in oil sand reservoirs with shale barriers. The peak oil production rate in the bottom-up assisted pressure drive (i.e., around 600 m\({}^{3}\)/day) was approximately three times that in the SAGD process (i.e., around 200 m\({}^{3}\)/day). The timing of the peak rate in the bottom-up assisted pressure drive was not affected, while the timing of the peak rate in the SAGD process was postponed to 1600 days.  
The cumulative oil production in the bottom-up assisted pressure drive was 20% higher than that in the SAGD process. The oil near the bottom of the formation can be recovered efficiently without drilling extra infill wells in the bottom-up assisted pressure drive. In addition, oil trapped above the shale barriers can be effectively displaced in the novel bottom-up assisted pressure drive process.  
The pressure difference in the bottom-up assisted pressure drive varied between 100 kPa and 30 kPa, which was greater than that in the SAGD process (approximately 30 kPa). The pressure drive is another mechanism for improving oil production. The calculated NPV in the bottom-up assisted pressure drive process was 27% higher than in the SAGD process. This was mainly attributed to the high oil production rate in the early stage of the process and high cumulative oil production. The inherent mechanisms associated with the bottom-up assisted pressure drive make it suitable for the development of oil sand reservoirs with shale barriers. The simulation studies in this work provide technical support for future field applications. It is recommended to perform physical laboratory experiments to further validate the mechanism obtained from simulation studies. In addition, field pilot tests are still required before implementing the commercial application of the bottom-up assisted pressure drive process.  
Writing--original draft, M.Y., S.W.; Writing--review and editing, Q.F., Y.Y. All authors have read and agreed to the published version of the manuscript.  
This research was funded by China Post-doctoral Science Foundation (2022M713466) and Independent Innovation Scientific Research Project (Science and Engineering) of China University of Petroleum (East China) (27 RA2102010).  
Not applicable.  
Data Availability Statement: Data sharing is not applicable to this article.  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline Discount rate & 10\% \\ Bitumen price & USD 36/bbl \\ Crude oil price of West Texas Intermediate & USD 60/bbl \\ Steam operating cost & USD 6/m\({}^{3}\) steam (CWE) \\ Drilling and completion cost & USD 1,500,000/well pair \\ \hline \hline \end{tabular}
\end{table}
Table 4: The relevant parameters for the NPV calculation.