## 2 Geological Characteristics of Reservoirs
### Mineral and Sensitivity Characteristics
#### 2.2.2 Result Analysis  
The results of X-ray diffraction experiments indicate that the reservoir is predominantly composed of quartz, dolomite, and calcite, with an average clay mineral content of 41% (Figure 1). It also contains minor amounts of siliceous material, terrestrial detritus, organic matter, and pyrite. The clay minerals commonly exhibit imogolite interbeds and sensitive mineral components such as pyrite, suggesting potential susceptibility to damage within the reservoir.  
The results of the reservoir sensitivity test indicate that the reservoir demonstrates moderate to strong water sensitivity (Figure 2), thus necessitating the use of an entry fluid with favorable anti-swelling properties.  
In almost fifty years of continuous exploration and development, the depletion-type mining method has been predominantly utilized. The outcomes of the two water injection development trials were inconclusive, resulting in a substantial reduction in oilfield pressure to 2-7 MPa, severe oil depletion, and a progressively deteriorating trial repair effect. Methods for enhancing oil recovery encompass gas injection, chemical flooding,microbial oil recovery, and electrokinetic methods [7; 41; 42]. While these approaches have specific advantages and disadvantages as well as application conditions (Table 1) [43; 44], it is challenging to fully apply them to the actual circumstances of the Da'anzhai oilfield.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Main Methods** & **Advantage** & **Disadvantages and Existing Problems** \\ \hline Microorganisms & Low investment cost, low consumption of chemicals and energy, greater economic competitiveness than other methods, and great potential. & The mechanism is complex, and when effective bacteria are cultivated and propagated in the oil layer, the native bacteria will multiply, causing formation damage and producing harmful gases such as H\({}_{2}\)S. \\ \hline Gas injection method & Mature technology; easy to achieve injection production balance; the damage to the oil well is minor; the process flow is simple and easy to manage; the economic benefits are greater than those of water injection. & Gas has a corrosive effect on the pipeline network, requiring a gas source with high input and making the pipelines prone to gas leakage. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Main methods for improving the recovery rate of low-permeability reservoirs at present.  
Figure 1: Whole-rock X-ray diffraction analysis of Da’anzhai formation in well A.  
Figure 2: Water sensitivity test curve of reservoir rock samples in Da’anzhai section.  
Due to its low-concentration use, minimal investment, and simple construction process, molecular deposition film driving technology can be effectively utilized in on-site trials using the existing injection well network and facilities. These trials have demonstrated significant increases in oil production. These attributes indicate that this technology has the potential to enhance the recovery rate of the Da'anzhai oilfield and is anticipated to emerge as a promising new method for improving water-drive-based recovery rates.