Measurement of Methane Emission from Gathering and Processing Facility: A Case Study in Typical Oil Field of China

Climate change has been ranked as one of the most severe challenges in the world. Greenhouse gas (GHG) emission was assumed to be the root cause. Carbon dioxide and methane are the most important GHG, while methane has a shorter atmospheric lifetime and higher global warming potential. Methane abatement was proposed as an indispensable measure to limit near-term global warming. Oil and gas (OG) production system are key methane emissions sources, with gathering and processing facility making high contribution. Measurement of methane emission from gathering and processing facility in an OG field was performed in China. Different components types, such as pressure gauge, valve, flange, connections, open-end pipeline and compressor system, were measured in 3 gathering facilities and 18 processing plants with a portable flame ionization detector (FID) and full range sampler. The component and facility based methane emission characteristics were confirmed. The results suggested 526 leak sources were identified from all sampled process components or sealing points. The leak frequency was founded to be 0.40% as a whole while it was 0.08% ~ 0.50% for gathering facility and 0.18% ~ 1.92% for processing plant, with gauge and valve category making up the highest portion. The open-end pipeline was more prone to suffer from leak problem than other type components. The flange category has a lowest population averaged emission rate of 0.16 L/min while compressor-related source has the highest mean value of 1.26 L/min. The population averaged emission rate was 0.72 L/min for gauge category and 0.22 L/min for valve category. In terms of facility-level emission rate, the population averaged value was determined to be 2.69 L/min per compressor system. The annual methane emission amount was estimated to be 45170.84 cubic meters (32.26 tons) for all sampled gathering and processing facilities. Different source category make disproportional contribution to total annual emission. The gauge category and compressor category predominates over other sources, contributing to more than 45.76% and 21.96% total emission respectively. The majority of emitted methane was attributed to a small portion of sources with emission rate higher than 1 L/min