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OS3C-1：MONITORING HYDRATES FORMATION BY GAS COMPOSITION CHANGES DURING GAS/CONDENSATE PRODUCTION WITH AA-LDHI: THE MEILLON FIELD TEST RESULTS.
发布时间:2014-07-28
Philippe GLÉNAT1, Jean-Michel MUNOZ1, Reza HAGHI2, Bahman TOHIDI2,3, Saeid MAZLOUM3 and Jinhai YANG2,3
1. TOTAL S.A., CSTJF, France ; 2. Institute of Petroleum Engineering, Heriot-Watt University, U.K.; 3. Hydrafact Ltd., Quantum Court, Heriot-Watt University Research Park, U.K.
MEILLON is a very mature sour gas condensate on-shore field in France close to the LACQ field producing for 50 years. One of a few remaining wells is still producing with a water cut of around 50% and GCR (Gas Condensate Ratio) of around 67,000 vol/vol. A buried 10” flow line transfers the well streams to a separator some 1.6 km away, where gas and liquid are separated before being transported to the main Processing Centre 20 kms away. Gas production is continuous through a pressure control value, whereas the small liquid produced is pumped on a batch basis by a level control value. Due to high wellhead temperature and medium wellhead pressure, there is no risk of hydrate formation in the transfer pipeline during production. However, the conditions inside the surface separator could be inside the hydrate stability zone, in particular in winter seasons and at nights. Temporary methanol injection at the wellhead was the primary method of preventing hydrate problems, however, due to increased water cut and successive changes in production modes due to the field maturing, it is no longer possible to inject methanol for hydrate prevention in winter and the well was produced until a hydrate plug formed at the separator liquid outlet. In winter 2013, injection of AA-LDHI at the well-head was implemented as hydrate plug prevention strategy to ensure the well uninterrupted production.
It was decided to use this opportunity and examine feasibility of monitoring changes in the gas composition as a means for detecting hydrate formation. The technique was developed at Heriot-Watt University as part of a Joint Industry Project. The technique is based on the fact that hydrates prefer certain molecules (in general large and round molecules), hence hydrate formation should result in a reduction in the concentration of these components in the gas phase. An online Gas Chromatograph (GC) was installed, taking gas samples from the gas outlet of the separator. The composition of the gas was analysed routinely as well as recording the system pressure and temperature. The results show that it is possible to detect hydrate formation by monitoring the separator outlet gas composition (e.g., C3 and/or i-C4 concentrations C1/C3 and/or C1/i-C4 ratios) despite the high GCR and the low frequency batch liquid production mode and some inconstancies related to the co-formation of sI and sII hydrates.
This field test demonstration indicates that this technique in addition to monitoring hydrate transport as liquid slurry with AA-LDHI could also be used for detecting early signs of hydrate formation which could have important field applications, such as optimising inhibitor injection timing/rates, preventing hydrate blockages, examining effectiveness of hydrate prevention strategies, etc...
In this communication we will present the details of the field trial, results obtained, lessons learned and some suggestions for future work.
1. TOTAL S.A., CSTJF, France ; 2. Institute of Petroleum Engineering, Heriot-Watt University, U.K.; 3. Hydrafact Ltd., Quantum Court, Heriot-Watt University Research Park, U.K.
MEILLON is a very mature sour gas condensate on-shore field in France close to the LACQ field producing for 50 years. One of a few remaining wells is still producing with a water cut of around 50% and GCR (Gas Condensate Ratio) of around 67,000 vol/vol. A buried 10” flow line transfers the well streams to a separator some 1.6 km away, where gas and liquid are separated before being transported to the main Processing Centre 20 kms away. Gas production is continuous through a pressure control value, whereas the small liquid produced is pumped on a batch basis by a level control value. Due to high wellhead temperature and medium wellhead pressure, there is no risk of hydrate formation in the transfer pipeline during production. However, the conditions inside the surface separator could be inside the hydrate stability zone, in particular in winter seasons and at nights. Temporary methanol injection at the wellhead was the primary method of preventing hydrate problems, however, due to increased water cut and successive changes in production modes due to the field maturing, it is no longer possible to inject methanol for hydrate prevention in winter and the well was produced until a hydrate plug formed at the separator liquid outlet. In winter 2013, injection of AA-LDHI at the well-head was implemented as hydrate plug prevention strategy to ensure the well uninterrupted production.
It was decided to use this opportunity and examine feasibility of monitoring changes in the gas composition as a means for detecting hydrate formation. The technique was developed at Heriot-Watt University as part of a Joint Industry Project. The technique is based on the fact that hydrates prefer certain molecules (in general large and round molecules), hence hydrate formation should result in a reduction in the concentration of these components in the gas phase. An online Gas Chromatograph (GC) was installed, taking gas samples from the gas outlet of the separator. The composition of the gas was analysed routinely as well as recording the system pressure and temperature. The results show that it is possible to detect hydrate formation by monitoring the separator outlet gas composition (e.g., C3 and/or i-C4 concentrations C1/C3 and/or C1/i-C4 ratios) despite the high GCR and the low frequency batch liquid production mode and some inconstancies related to the co-formation of sI and sII hydrates.
This field test demonstration indicates that this technique in addition to monitoring hydrate transport as liquid slurry with AA-LDHI could also be used for detecting early signs of hydrate formation which could have important field applications, such as optimising inhibitor injection timing/rates, preventing hydrate blockages, examining effectiveness of hydrate prevention strategies, etc...
In this communication we will present the details of the field trial, results obtained, lessons learned and some suggestions for future work.
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