# Matching of Water Breakthroughs in a Low-Resistivity Oil Reservoir Using Permeability Anisotropy
## 5 Conclusions  
1. The Lower Haushi Sandstone (LHS) oil reservoir has a complex lithological architecture that is transitional from marine to basinal due to its position on the continental slope. The LHS reservoir is divided into two parts by a shale layer. The uppermost part of the upper layer is tight across almost the entire thickness, with high water saturation confirmed by a well test. The reservoir was waterflooded early, which could be due to uncertainties in water saturation and fluid contact caused by low resistivity, presenting unclear vertical and lateral hydrology. 2. The analysis of all factors showed that the low resistivity was caused by the high salinity of the Formation water in combination with the well-connected porous system of the homogeneous sandstone that is characterized by a cementation factor of 1.6, permeability anisotropy with a Kv/Kh = 1, and the presence of fissures, indicating that such a porous system can be highly electrically conductive. In contrast, the Dolomite Drain oil reservoir above the LHS with a different porous system demonstrated high resistivity. Figure 15: Petrophysical models of water saturation of porous LHS-UD reservoir: before the start of production (**a**) and at the end of production with (**b**) Kv/Kh = 0.1 and (**c**) Kv/Kh = 1. Red, orange, and yellow colors indicate the areas of remaining oil. 3. Using Petrel software, simulation was performed to test varying Kv/Kh ratios and relative permeability curves to understand the reason for the early water breakthrough and obtain a better history match with production data. An increase in Kv/Kh from 0.1 used by default in the simulation to 1 increased the WPR substantially in Well G and Well B throughout the production period, and about two times higher in Well C during the first 2 years. This provided a better match to the observed data and is indicative of vertical water inflow. However, Kv/Kh = 0.1 provided a better match in Well A and Well E, which can be explained by their location on the edges of the structures and lateral water inflow from the adjacent areas. The high water influx can be attributed to the faster-than-expected water encroachment due to the high hydrodynamic connectivity in all directions leading to the fast depletion of the reservoir. The shift of the relative permeability ratio to more oil-wet in some production periods shows the wettability changes and can help in history matching. 4. The depletion of the reservoir is confirmed by the two areas remaining unswept in the LHS reservoir due to the absence of wells: to the NW of Wells C and F and to the SE of Wells E and G. With Kv/Kh = 1, the areal size and the oil saturation in the potentially unswept areas were greater. The remaining oil in the tight upper part of LHS-UD requires unconventional methods of oil extraction. Methodology, S.R., U.T. ; software, M.A.-M., U.T. ; validation, S.R., M.A.-M. and U.T. ; formal analysis, P.S. ; investigation, S.R., P.S. and U.T. ; data curation, S.R., U.T., and M.A.-M.; writing--original draft preparation, S.R. ; writing--review and editing, S.R., U.T. and P.S. ; visualization, S.R., U.T., M.A.-M. and P.S. ; supervision, S.R. ; project administration, S.R., U.T. ; funding acquisition, P.S. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Data is contained within the article. The authors would like to express their sincere gratitude to the company that provided the field data used in this study. Their valuable contribution and support played a critical role in the success of this research project. Additionally, the authors would like to thank Schlumberger for granting us academic licenses for Petrel, Intersect, and Techlog, which were instrumental in the analysis and interpretation of the data. Without the generous support and collaboration from these organizations, this study would not have been possible. The authors declare no conflict of interests.