# Matching of Water Breakthroughs in a Low-Resistivity Oil Reservoir Using Permeability Anisotropy
## 4 Results and Discussion
### Influence of Kv/Kh on the Production Curves  
The factor of similar horizontal and vertical permeabilities can play a substantial role in causing early water breakthrough. In this study, we focused on the influence of permeability anisotropy on the simulation results. The details of the simulation procedure can be found in [14; 15]. In the base-case simulation, a Kv/Kh of 1/10 was used by default in the history matching of OPR and WPR. Several Kv/Kh ratios were attempted in our simulations, such as 1:100, 1/1, 2/3, 10/1 and 20/1 for the comparison with the base-case. For some wells, slight differences between the results were observed for cases with 1/1 and 2/3, but the simulation appeared to be insensible to higher ratios when a Kv/Kh of 10/1 was compared to 20/1. In addition, there was no difference between the results of 1/10 and 1/100. Therefore, only the results for the cases with 1/10 and 1/1 were compared. Well D was perforated in the lower porous part of the LHS-UD and the upper part of LHS-LD (Figure 8) and no water breakthroughs were observed in the well. In the simulation case with Kv/Kh = 1/1, WPR with a value close to zero was predicted,  
Figure 8: Gamma ray (GR) logs, resistivity logs (ILD, LLS), density porosity (FOR), plots in reverse scale of porosity (PHI) calculated using EPT (TPL), neutron (NPHI) and density (PHIT) logs, average of neutron and density porosity (PHIT_ND), water saturation (Sw) calculated using Archie and Simandoux equations, and perforations in Well E of LHS reservoir. which better matches the actual WPR below 20 STB/d. On the contrary, the case with Kv/Kh = 1/10 predicted a higher WPR. Moreover, Well G was perforated in LHS-UD and LHS-LD, but the production has also occurred from Gharif Basal Sandstone. In this well, the water breakthroughs began in 1983 and ended in 1985, with a maximum of 2200 STB/d. The case with Kv/Kh = 1/1 predicted WPR of about 900 STB/d on average, but one month earlier than the actual date. The case with Kv/Kh = 1/10 predicted significantly lower WPR but matched more accurately the start of the water breakthrough. The end of the water breakthrough was predicted by both cases on the same date, matching the observed data (Figure 9a). In Well C, WPR predicted by the case with a 1/1 ratio is two times higher than that predicted by the case with 1/10 during the first year of production. In the following three years, the WPR for the case with 1/10 gradually increased to the same WPR of 1000 STB/d on average and became similar to the WPR of the 1/1 case between 1986 and 1987. Water production rate (WPR) using Kv/Kh of 1 and 0.1: (a) Well G, (b) Well B. Kv/Kh = 1 scenario better match to WPR than 0.1 The field-observed WPR between 1983 and 1987 was higher, varying between 3000 and 4000 STB/d. The comingled production started on the same date from LHS and Basal Gharif, which indicates that the water could be from Basal Gharif. In Well B, the comingled production started with LHS and DD in 1982 and the water breakthrough started at the end of June 1983, reaching a maximum of 2700 STB/day at the end of 1987. WPR of 650 STB/d on average was predicted using 1/1, while WPR below 100 STB/d was predicted using 1/10 (Figure 9b). In Well E, the WPR was below 300 STB/day, which is much lower than in Wells C and B. From 1986 to 1993, Kv/Kh = 1/10 predicted the beginning of water inflow 3 months earlier, close to the WPR in 1988-1990, but about two times higher than in 1990-1994. Similar to Well D, 1/1 predicted a WPR near zero, which indicates that the water inflow was lateral (Figure 10a). In Well A, the WPR predicted by Kv/Kh = 1/10 is higher by 500 STB/day than the actual 1000 STB/day on average. The match provided by 1/10 indicates that the water inflow was in the lateral direction. The case using the 1/1 ratio predicted significantly higher WPR, illustrating the severity of the Kv/Kh effect. However, this scenario is not unrealistic considering that Well A is located at the edge of the structure.