Casing gas refers to the gas that escapes from the annulus of oil well casing during the process of oil and gas extraction. It has the following characteristics:
Complex composition
The main component of casing gas is hydrocarbon gas, such as methane, ethane, propane, etc. Among them, methane usually accounts for a large proportion and is an important component of casing gas. These hydrocarbon gases are flammable and can be recycled as energy materials.
Containing non hydrocarbon gases: In addition to hydrocarbon gases, casing gases also contain a certain amount of non hydrocarbon gases such as carbon dioxide, hydrogen sulfide, nitrogen, etc. The presence of carbon dioxide may affect the calorific value and combustion performance of the gas; Hydrogen sulfide has strong corrosiveness and can cause corrosion to equipment and pipelines. At the same time, its toxicity is also harmful to human health and the environment; Nitrogen will reduce the calorific value and combustion efficiency of the gas.
Wide range of pressure and temperature
Large pressure variation: The pressure of casing gas varies greatly due to factors such as the depth of the oil well, geological conditions, and production stage. In the early stage of oil well exploitation, the gas pressure in the casing may be high, reaching several megapascals or even higher; As mining progresses, the pressure will gradually decrease, possibly to several hundred kilopascals or even lower. This wide range of pressure changes poses certain challenges for the recovery and treatment of casing gas, requiring the selection of appropriate equipment and processes to adapt to gas recovery under different pressures.
The temperature difference is significant: the temperature of the casing gas will also vary depending on the depth of the oil well and the production conditions. Generally speaking, the temperature of casing gas in deep oil wells is relatively high, reaching over 100 ℃; The gas temperature in shallow oil wells is relatively low. The change in temperature can affect the physical properties and chemical activity of gases, thereby affecting the recovery efficiency of gases and the operational performance of equipment.
Unstable traffic
Change with production stage: Throughout the entire lifecycle of the oil well, the flow rate of casing gas will undergo significant changes with different production stages. In the early stage of production, the oil well has a high output and the gas flow rate in the casing is relatively large; As the oil well gradually dries up and production decreases, the flow rate of casing gas will also decrease accordingly. The instability of this flow requires consideration of the flexibility and adaptability of the system when designing a casing gas recovery system to cope with flow changes at different stages.
Affected by production conditions: The production conditions of oil wells, such as the working status of pumping units and fluctuations in wellhead pressure, can also affect the flow rate of casing gas. For example, changes in the stroke and number of strokes of a pumping unit, as well as sudden fluctuations in wellhead pressure, can all cause instantaneous changes in the flow rate of casing gas. Therefore, it is necessary to monitor and regulate the flow rate of casing gas in real time to ensure the stable operation of the recovery system.
May contain impurities
Solid particle impurities: Due to the complexity of geological conditions in oil wells, casing gas may carry a certain amount of solid particle impurities, such as sand particles, rock debris, etc. These solid particles can cause wear and tear on equipment such as compressors and pipelines, reduce their service life, and even lead to equipment blockage, affecting the normal operation of gas recovery.
Liquid impurities: In addition, the casing gas may also contain small amounts of liquid impurities such as water, oil droplets, etc. The presence of liquids can affect the compression performance of gases, increase the energy consumption of compressors, and may also lead to pipeline corrosion and equipment failure. Therefore, before the recovery of casing gas, it is usually necessary to pre treat the gas to remove impurities.
Flammable and explosive
Explosion limit range: The hydrocarbon components in the casing gas make it flammable and explosive. Different hydrocarbon gases have different explosion limit ranges, for example, the explosion limit of methane is generally between 5% and 15%. When the concentration of casing gas in the air is within the explosive limit range, it may explode when encountering a fire source or energy source, posing a serious threat to production safety.
Safety risk prevention: Given the flammability and explosiveness of casing gas, strict safety measures must be taken during the recovery, treatment, and transportation of casing gas, such as using explosion-proof equipment, installing gas leak monitoring devices, and strengthening ventilation, to prevent gas leaks and explosion accidents.
