Performance of Horizontal Wells, Safah Field, Oman
- Hsiu-Kuo Chen (Occidental of Oman)
- Document ID
- Society of Petroleum Engineers
- Middle East Oil Show, 3-6 April, Bahrain
- Publication Date
- Document Type
- Conference Paper
- 1993. Society of Petroleum Engineers
- 5.2.1 Phase Behavior and PVT Measurements, 5.7.2 Recovery Factors, 3 Production and Well Operations, 1.6.6 Directional Drilling, 2 Well Completion, 3.3.1 Production Logging, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 5.1.2 Faults and Fracture Characterisation, 5.5 Reservoir Simulation, 1.6 Drilling Operations, 4.5 Offshore Facilities and Subsea Systems
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This paper reviews the performance of seven horizontal wells completed between October 1990 and February 1992 in the Safah field, the Sultanate of Oman. The horizontal well sections range from 1985 to 4718 ft. The well performance indicates that there is no direct correlation between initial well productivity index (PI) and length of the horizontal section. The long-term PI of the horizontal wells depends on the GOR of the well. The average PI of the horizontal wells is about 10 times that of the average vertical wells. It takes about one fifth of the time to produce a given production with a horizontal well. The excellent performance of the horizontal wells has increased oil production. The use of horizontal wells is expected to increase the overall recovery for the Safah field.
Safah field, located 415 kilometers west of Muscat in the Sultanate of Oman, produces oil from a lime mudstone (average permeability of 5 md) of the Upper Shuaiba Formation (Lower Cretaceous age). The field contains 650 million barrels of oil-in-place and 54 billion cubic feet of gas cap. The field is divided into East and West lobes. The East lobe is subdivided into Northeast and Southeast lobes based on PVT properties (Fig. 1). The Northeast lobe contains saturated oil with a gas oil contact at 6015 ft subsea and an oil water contact (40% water saturation) at 6115 ft subsea. The Southeast lobe has undersaturated oil with an oil water contact at 6125 ft subsea.
Prior to drilling the first horizontal well in October 1990, a total of 114 vertical wells were drilled in the Safah field. The wells completed in the gas cap area have experienced early gas coning. A reservoir simulation study predicted an oil recovery factor from drilling 124 acre vertical wells of less than 6% of the OOIP under the gas cap. The study also showed that the recovery factor can be improved by drilling horizontal wells under gas cap.
The first two horizontal wells (S-115 and S-116) completed in October and December 1990 showed extremely good performance. The oil production rate for S-115 was about 1500 BOPD and for S-116 was around 1800 BOPD. These oil rates are about five times the rates for average new vertical wells. Both wells were producing with gas oil ratios of less than 2000 SCF/B. The drilling and completion cost was 2.5 to 3.5 times the cost for the average vertical well. Based on the encouraging results of these horizontal wells, five more horizontal wells were drilled during 1991 and 1992.
This paper briefly reviews Safah horizontal drilling and completions and production logging in the horizontal well. The paper discusses in detail the performance of the seven horizontal wells in the Safah field.
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