Methane emission rate estimate using airborne measurement at offshore oil platforms in Newfoundland and Labrador, Canada

Methane (CH4) measurements are needed to better understand emissions from oil and gas sources. While many CH4 measurement studies have been done in Canada, they have not yet targeted offshore production from which low emission intensities are reported by industry. For this study, a Twin Otter aircraft was equipped with a Picarro 2210-i gas analyzer and an Aventech wind measurement system (AIMMs_30) to measure CH4 emissions from three oil production facilities in offshore Newfoundland and Labrador. Each facility was visited three times to account for daily variability. Measured concentrations were used to estimate emission rates and production-weighted intensities using two different methods, Top-down Emission Rate Retrieval Algorithm (TERRA), a mass conservation technique developed by Environment and Climate Change Canada, and a Gaussian Dispersion method (GD). Overall, TERRA mass balance-derived emission rates from our measurements were 2,890±3,027 m3 CH4 day-1(GD=7,721 m3 CH4 day-1), 3,738 ±7,199 m3 CH4 day-1 (GD=13,131 m3 CH4 day-1) and 7,975±4,453 m3 CH4 day-1 (GD=7,242 m3 CH4 day-1), respectively for SeaRose, Hibernia and Hebron. Based on results from both TERRA and Gaussian dispersion the weighted average was (considering number of samples in each method) 5,000 m3 CH4 day-1 (3.35 tonnes CH4 day-1), which is comparable to the federally reported estimate of 8,037 m3 CH4 day-1 of federal estimates, reported in 2019. Production-weighted methane intensities calculated using measured emission rates and reported oil production show that Canadian offshore production ranges from 0.4-2.2 MJ emitted/MJ produced, making it among the least methane-intensive oil produced in Canada.甲烷（CH₄）监测数据可为深入解析油气源排放特征提供关键支撑。尽管加拿大已开展大量甲烷监测相关研究，但目前尚未针对海上油气生产平台开展相关工作——尽管行业报告显示此类平台的排放强度较低。本研究依托一架双水獭（Twin Otter）型航空器，搭载Picarro 2210-i型气体分析仪与Aventech风力测量系统（AIMMs_30），对纽芬兰与拉布拉多近海的三座石油生产设施开展甲烷排放监测。为表征每日排放的波动特征，每座设施均完成三次监测飞行。本研究采用两种方法，基于实测浓度估算排放速率与产量加权排放强度：其一为加拿大环境与气候变化部开发的质量守恒技术——自上而下排放速率反演算法（Top-down Emission Rate Retrieval Algorithm，TERRA）；其二为高斯扩散法（Gaussian Dispersion Method，GD）。整体而言，基于本次实测数据经TERRA质量守恒法反演得到的排放速率，依次为SeaRose平台2890±3027 立方米甲烷/日（GD法结果为7721立方米甲烷/日）、Hibernia平台3738±7199 立方米甲烷/日（GD法结果为13131立方米甲烷/日）、Hebron平台7975±4453 立方米甲烷/日（GD法结果为7242立方米甲烷/日）。综合TERRA与GD法的结果，结合各方法的样本量计算得到加权平均排放速率为5000立方米甲烷/日（折合3.35吨甲烷/日），该结果与加拿大联邦2019年报告的8037立方米甲烷/日的估算值具有可比性。基于实测排放速率与公开原油产量数据计算得到的产量加权甲烷排放强度显示，加拿大近海石油生产的排放强度区间为0.4~2.2兆焦排放/兆焦产出，属于加拿大国内甲烷排放强度最低的石油生产类型之一。