Greenhouse gas emissions from oilfield-produced water in Shengli Oilfield, Eastern China

Greenhouse gas (GHG) emissions from oil and gas systems are an important component of the GHG emission inventory. To assess the carbon emissions from oilfield-produced water under atmospheric conditions correctly, in situ detection and simulation experiments were developed to study the natural release of GHG into the atmosphere in the Shengli Oilfield, the second largest oilfield in China. The results showed that methane (CH₄) and carbon dioxide (CO₂) were the primary gases released naturally from the oilfield-produced water. The atmospheric temperature and release time played important roles in determining the CH₄ and CO₂ emissions under atmospheric conditions. Higher temperatures enhanced the carbon emissions. The emissions of both CH₄ and CO₂ from oilfield-produced water were highest at 27°C and lowest at 3°C. The bulk of CH₄ and CO₂ was released from the oilfield-produced water during the first release period, 0–2 hr, for each temperature, with a maximum average emission rate of 0.415 g CH₄/(m³·hr) and 3.934 g CO₂/(m³·hr), respectively. Then the carbon emissions at other time periods gradually decreased with the extension of time. The higher solubility of CO₂ in water than CH₄ results in a higher emission rate of CH₄ than CO₂ over the same release duration. The simulation proved that oilfield-produced water is one of the potential emission sources that should be given great attention in oil and gas systems.