Crow Daniel J G, Balcombe Paul, Brandon Nigel, Hawkes Adam D
Sustainable Gas Institute, Imperial College London, London SW7 2AZ, UK.
Sustainable Gas Institute, Imperial College London, London SW7 2AZ, UK; Department of Chemical Engineering, Imperial College London, London SW7 2AZ, UK.
Sci Total Environ. 2019 Jun 10;668:1242-1258. doi: 10.1016/j.scitotenv.2019.03.048. Epub 2019 Mar 7.
Greenhouse gases (GHGs) produced by the extraction of natural gas are an important contributor to lifecycle emissions and account for a significant fraction of anthropogenic methane emissions in the USA. The timing as well as the magnitude of these emissions matters, as the short term climate warming impact of methane is up to 120 times that of CO. This study uses estimates of CO and methane emissions associated with different upstream operations to build a deterministic model of GHG emissions from conventional and unconventional gas fields as a function of time. By combining these emissions with a dynamic, techno-economic model of gas supply we assess their potential impact on the value of different types of project and identify stranded resources in various carbon price scenarios. We focus in particular on the effects of different emission metrics for methane, using the global warming potential (GWP) and the global temperature potential (GTP), with both fixed 20-year and 100-year CO-equivalent values and in a time-dependent way based on a target year for climate stabilisation. We report a strong time dependence of emissions over the lifecycle of a typical field, and find that bringing forward the stabilisation year dramatically increases the importance of the methane contribution to these emissions. Using a commercial database of the remaining reserves of individual projects, we use our model to quantify future emissions resulting from the extraction of current US non-associated reserves. A carbon price of at least 400 USD/tonne CO is effective in reducing cumulative GHGs by 30-60%, indicating that decarbonising the upstream component of the natural gas supply chain is achievable using carbon prices similar to those needed to decarbonise the energy system as a whole. Surprisingly, for large carbon prices, the choice of emission metric does not have a significant impact on cumulative emissions.
天然气开采产生的温室气体（GHG）是生命周期排放的重要贡献者，在美国人为甲烷排放中占很大比例。这些排放的时间和规模都很重要，因为甲烷的短期气候变暖影响高达二氧化碳的120倍。本研究使用与不同上游作业相关的二氧化碳和甲烷排放估计值，构建了常规和非常规气田温室气体排放随时间变化的确定性模型。通过将这些排放与天然气供应的动态技术经济模型相结合，我们评估了它们对不同类型项目价值的潜在影响，并确定了各种碳价格情景下的搁浅资源。我们特别关注甲烷不同排放指标的影响，使用全球变暖潜能值（GWP）和全球温度潜能值（GTP），采用固定的20年和100年二氧化碳当量值，并基于气候稳定目标年份以时间依赖的方式进行计算。我们报告了典型气田生命周期内排放的强烈时间依赖性，并发现提前稳定年份会显著增加甲烷对这些排放贡献的重要性。利用单个项目剩余储量的商业数据库，我们使用模型量化了美国当前非伴生气储量开采产生的未来排放量。至少400美元/吨二氧化碳的碳价格可有效将累计温室气体减少30 - 60%，这表明使用与使整个能源系统脱碳所需的碳价格相似的价格，天然气供应链上游部分的脱碳是可以实现的。令人惊讶的是，对于高碳价格，排放指标的选择对累计排放量没有显著影响。
