# Matching of Water Breakthroughs in a Low-Resistivity Oil Reservoir Using Permeability Anisotropy
## 4 Results and Discussion
### Clay Type Using a Juhasz Plot  
The logging curves of GR, porosity, and water saturation are shown for two wells in Figures 5 and 6. The LHS reservoir is divided into two sections, the upper section (LHS-UD) and the lower section (LHS-LD), by a shale layer. The uppermost section (approximately 4 m) of the LHS-UD reservoir consists of tight sandstone with porosity values significantly below 6%. Below this zone, thin layers have even lower porosities, measuring less than 2%. This upper layer of LHS-UD can be characterized as a tight oil reservoir due to its low porosity and permeability. Such tight oil sandstone reservoirs attract much attention in many countries, and especially in China, they present huge oil resource potential [29].  
Due to the very low porosity, and despite resistivity in the range of 10-50 Ohmm, the Sw at the top of LHS-UD results in values close to unity. Figures 5 and 6 depict the water-bearing low-porosity zones (shown in blue) in the uppermost 4 m of LHS-UD. This observation suggests a potential re-evaluation of the initial assumption that oil is located above the water in the reservoir. Figure 7 depicts the zonation scheme used in the model.  
dispersed clay is below 7%. In other parts also with high porosity, the Vsh of dispersed clay varies between 7 and 15%.  
Figure 5: Logging data profiles of Well G (**left**): gamma ray log (GR), porosity determined using density log and water saturation. The Juhasz plot (**right**) shows the distribution of different clay types at respective depths in different colors in the LHS reservoir. Colors indicate layers.  
Figure 6: Logging data profiles of Well E (**left**): gamma ray log (GR), porosity determined using density log and water saturation. The Juhasz plot (**right**) shows the distribution of different clay types at respective depths in different colors in the LHS reservoir. Colors indicate layers.  
In Well E, the lowest 8 m of LHS-LD have resistivity below 1 Ohmm, resulting in Sw > 80%, which indicates a water zone and oil-water contact (OWC). This can be explained by the fact that this well was drilled 7 years later than Well G, and this water zone at the bottom shows a rise in OWC rather than water breakthroughs. This also shows that in the porous part, the contrast between oil and water is sufficient to separate them even at such low resistivity, implying that the oil zone in Well G reaches to the base of the reservoir. However, this water influx from the aquifer and the logging response of the invading water may not be the same as the connate water saturation.  
Hence, the lower parts of LHS-UD and LHS-LD sandstone are mostly clean homogeneous sandstone with porosities of up to 23% on average, with a low fraction of dispersed shale, which should not noticeably affect the water saturation. A sufficient contrast between oil and water zones is generated irrespective of the low resistivity. However, in the tight part of LHS-UD, low porosity with a shale volume of about 20-25%, even at higher resistivity, results in high water saturation due to a low contrast between oil and water.