On Application of Horizontal Wells to Reduce Condensate Blockage in Gas Condensate Reservoirs
- Nathan Miller (Texas A&M U.) | Hadi Nasrabadi (Texas A&M U at Qatar) | Ding Zhu (Texas A&M U.)
- Document ID
- Society of Petroleum Engineers
- International Oil and Gas Conference and Exhibition in China, 8-10 June, Beijing, China
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
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Natural gas is an important source for global energy. It will play a more important role in the future due to increasing energy demands, existing constraints in oil production, and environmental concerns for other fossil fuel types. Much of the current gas reserves can be found in gas-condensate reservoirs. These reservoirs, from a recovery and deliverability standpoint, can have significant differences from oil reservoirs. When the pressure, either in the wellbore or in the reservoir, drops below the dew point pressure, a liquid condensate phase appears and reduces gas production significantly. Several methods have been suggested to handle the condensate blockage problem: hydraulic fracturing, wettability alteration, Huff ‘n' Puff gas injection, and nonconventional wells. In this work, we study the application of horizontal wells in a giant gas-condensate reservoir (North Field-Qatar) to reduce the condensate blockage. We try to address a critical question of what fraction of increased gas production in a horizontal well is due to increased formation contact and what fraction results from condensate blockage reduction. Horizontal wells have smaller drawdown pressures than vertical wells, which leads to a delay in reaching the dew point pressure compared to vertical wells. Our results indicate that once the dew point pressure is reached and oil saturation is formed in the reservoir, the magnitude of oil saturation buildup in the near wellbore is lower in a horizontal well than a vertical well. The ratio of horizontal well PI to vertical well PI increases after the dew point. The fact that the PI increased after reaching the dew point indicates that this increase in productivity index is directly due to the ability of the horizontal well to reduce condensate blockage in the near wellbore. The PI in the vertical well case is decreasing significantly once the dew point pressure is reached, while the PI in the horizontal well seems to remain steady even after the dew point pressure is reached.
Much of the 6,183 trillion cubic feet of worldwide gas reserves can be found in gas-condensate reservoirs. For this reason gas condensate reservoirs are important to today's energy supply/demend problem. Some of the largest gas-condensate reservoirs in the world include the Arun Field in Indonesia, the Cupiagua Field in Colombia, the Karachaganak Field in Kazakhstan, the North Field in Qatar which borders with the South Pars Field in Iran, and the Shtokmanovskoye Field in the Russian Barents Sea. All of these large gas condensate fields have one thing in common: condensate blockage. Condensate blockage occurs due to the formation of liquid phase around the wellbore as pressure decreases below dew -point pressure. Production performance can
decrease dramatically if these condensate banking effects are not understood at the start of field development.
The initial producing gas-oil ratio, the gravity of the stock-tank liquid, and the color of the stock-tank liquid are three fluid properties that can be used in the field to determine what type of fluid is in a reservoir. Retrograde gases exhibit a lower GOR limit of 3,300 scf/stb and an upper GOR limit of 150,000 scf/stb. Retrograde gases have stock-tank liquid gravities between 40° and 60° API, and can be lightly colored, orange, brown, greenish, or water-white in color. Retrograde gases are referred to as retrograde gas-condensates, retrograde condensate gases, gas condensates, and condensates (McCain 1990).
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