Understanding of Oilfield Souring and Effective Monitoring: A Case Study
- Ardian Nengkoda (Petroleum Development Oman) | Mohammad Hajri (Petroleum Development Oman) | John Michael Walsh (Petroleum Development Oman) | Ron Hofland (Shell International E&P) | Hilal Barhi (Petroleum Development Oman) | Khalid Nasser Al-Ghammari (Petroleum Development Oman)
- Document ID
- Society of Petroleum Engineers
- SPE Middle East Oil and Gas Show and Conference, 15-18 March, Manama, Bahrain
- Publication Date
- Document Type
- Conference Paper
- 2009. Society of Petroleum Engineers
- 4.1.5 Processing Equipment, 5.1.1 Exploration, Development, Structural Geology, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.2.3 Materials and Corrosion, 5.2 Reservoir Fluid Dynamics, 5.8.3 Coal Seam Gas, 4.6 Natural Gas, 4.2 Pipelines, Flowlines and Risers, 3.1 Artificial Lift Systems, 4.1.9 Heavy Oil Upgrading, 3.1.6 Gas Lift, 5.2.1 Phase Behavior and PVT Measurements, 4.1.2 Separation and Treating, 5.4.2 Gas Injection Methods
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In the X oilfield Sultanate of Oman, water has been injected since June 2001 for EOR purposes. The water supply sources, was used through 4 dedicated injection wells, at a maximum total rate of 4000 m3/d in early 2003. By end of April 2003 the injection water source was switched to produce water, and separated at in line separator. The production wells suddenly turned to produced high H2S, while the well injectivity decline around 50% and levels have caused concern for on going Field Development scenarios. Meanwhile, in opposite, in Y oilfield, when discovered, the field was found to be sour, hence production facilities were designed for sour service. Occasional monitoring confirmed high H2S levels to prevail, but also showed an alarming increase with time, casting doubts on future integrity assurance. As the materials used in the X and down stream receiving facilities are not to be NACE 175 souring compliant and consider H2S released are hazard for safety. Starting December 2005, production chemistry and reservoir study have initiated an integrated H2S Monitoring and implemented a Mitigation Program by improving H2S onsite measurement and method revision, adopted instrument calibration accuracy, established frequent surveillance teams, investigated the caused of souring by Sulphur Isotope methodology for both X and Y field, and monitor the produce solid. Overall its improved business performance, HSE awareness, saving the plant upgrade cost, and finally now days in November 2008, the H2S level from X Field become traces and the area is safe for full field development.
In the X field Sultanate of Oman, water has been injected since June 2001 for enhanced oil recovery purposes. Initially Umm Er Radhumma (UeR) water, featuring high H2S levels in this area, was used for this, as obtained from 6 water supply wells (WSW), through 4 dedicated injection wells, at a maximum total rate of some 3900 m3/d, reached in April 2003. By end of April 2003 the injection water source was switched to produced water, as separated in the in-line separator at the central X processing facility.
The increasing H2S levels have caused concern for future production scenarios, as the materials used in the X field subsequent processing facilities at down stream facilities are reported not to be Natl. Assn. of Corrosion Engineers (NACE) 175 compliant. This needs to be addressed further, as H2S levels seem to level out, and the production system seems to cope with current conditions.
Meanwhile, in opposite, having started production in the early 1970, Y field produces from the S (sour) and the H (sweet). Both reservoirs are mature, needing artificial lift to sustain high water cut production. Currently, the S sour wells are equipped with ESPs, and the H wells are being gaslifted. Development plans for the S are currently being progressed. Whilst studies are being conducted on possible recovery mechanisms, recent reports of sharply increasing H2S levels have caused concerns on HSE and facility integrity in future operational modes. In order to place this into project perspective, a study was commissioned to both X and Y oilfield to verify H2S trends, understand their root cause and predict possible future H2S scenarios.
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