## 2 Wettability Measurement Methods
### Methods Based on Spontaneous Absorption of Liquid by Rock and Capillary Pressure  
#### 2.1.1. _A_mott-Harvey Test  
The Amott-Harvey test is a reliable method for determining the wettability of reservoir rocks at the core scale and consists of four steps aimed at assessing wettability. Two of these stages involve spontaneous imbibition processes (Figure 1: steps 1 and 3), while the other two involve forced displacement processes (Figure 1: steps 2 and 4) [6; 7]. First, a sample pre-saturated with oil is immersed in the Amott apparatus for an extended period, and the volume of oil spontaneously displaced by water is measured (Figure 1: steps 1). Next, water is forcibly injected into the core using a centrifuge, and the total volume of displaced oil is recorded (Figure 1: steps 2). In steps 3 and 4, the procedure is repeated, but this time, the fluids are reversed: oil is first spontaneously imbibed into the sample, followed by its forced injection to displace water.  
The injection pressure plays a critical role in ensuring the correct execution of the test. It must be high enough to ensure efficient fluid displacement from the rock but not so high as to damage the sample or create improper flow conditions [73; 74]. During forced imbibition, it is important to control the injection pressure to achieve a fluid flow rate that accurately reflects reservoir conditions. This allows for more effective modeling of real conditions and the acquisition of reliable data on fluid displacement and wettability indices.  
The test can be described by the conduction of two Amott measurements in which the Amott water (\(I_{w}\)) and oil (\(I_{o}\)) indices are determined as follows [6]:  
\[I_{w}=\frac{V_{oi}}{V_{ot}},\;\;I_{o}=\frac{V_{wi}}{V_{wt}} \tag{1}\]  
where \((V_{oi})\) is the volume of oil displaced by spontaneous imbibition of water, and \((V_{ot})\) denotes the total volume of oil displaced by spontaneous and forced imbibition of water; \((V_{wi})\) and \((V_{wt})\) represent the volume of water displaced by the spontaneous imbibition of oil and the total volume of water displaced by the spontaneous and forced imbibition of oil, respectively (Figure 1). The Amott-Harvey wettability index \((I_{AH})\) is defined as the difference between \((I_{w})\) and \((I_{o})\)[6]:  
\[I_{AH}=I_{w}-I_{o} \tag{2}\]  
Figure 1: Amott wetting technique [7].  
The values of the Amott-Harvey wettability index \(I_{AH}\), calculated by Equation (1), are depicted in Table 1. The Amott-Harvey wettability index \((I_{AH})\) ranges from \(-1\) to \(1\) describing strongly oil-wet (\(I_{AH}=-1\)), strongly water-wet (\(I_{AH}=1\)) and mixed-wet (\(I_{AH}\) from \(-0.3\) to \(0.3\)) rocks.  
The main limitation of the Amott-Harvey test is its insensitivity to the wettability of samples with values close to neutral [75]. Additionally, this test is time-consuming, as there is no clear criterion for determining the endpoint of the spontaneous imbibition stage for either water or oil. In some experiments, this stage may take around 20 h, but in several studies, the imbibition time extended up to 10 days [8; 76; 77]. Insufficient exposure of samples during the spontaneous imbibition stage can lead to the underestimation of their wettability [75; 78].