scope:

The schematic presented in Figure 1-1 depicts the overall building blocks that might be considered in developing a comprehensive emissions inventory. The other blocks, aside from directly operated emission sources, should to be evaluated carefully to prevent either under- or over-estimation of facility/company/industry segment emissions.

Source applicability considerations and other boundary issues are often an integral part of the emissions inventory development process. Although answers to the following questions are company-specific decisions, some of the issues considered by the API along with some recommended approaches are summarized below:

• Issue: What compounds or emissions should be targeted?

Recommendation: Focus on carbon dioxide (CO 2) and methane (CH 4) first, assess other GHGs later if industry is a significant emitter.

• Issue: What industry sectors should be included?

Recommendation: It is advisable to have a common framework for all sectors, from well-head to retail. Nonetheless, special attention is needed for specific operating practices and unique process units.

• Issue: Should the inventory scope include all operations globally?

Recommendation: The methods compiled are universally applicable. Specific needs for local, national, regional, or global summaries should determine the inventory scope. In applying the methods globally, care should be taken to allow for regional differences in the definition of standard conditions and fuel properties specifications.

• Issue: Should the inventory account for emissions attributable to imported and/or exported steam and power?

Recommendation: The methodology allows for both calculational approaches - emissions from directly operated devices along with indirect emissions associated with utilities use. If such emissions are included, separate, clearly labeled summaries should be used to differentiate between "direct" and "indirect" emissions to prevent double counting sources in national inventories.

Issue: Should the inventory account for emissions from joint ventures or other non-wholly owned enterprises?

Recommendation: Two parallel inventories could be developed, one based on "100% as operated" approach, while the second tracks the "equity share" in facilities and operations.

This compendium represents a compilation of methodologies for estimating greenhouse gas emissions. It is strongly recommended that any approach taken should be well annotated, and all input information recorded, to allow for future changes as new information becomes available.

Methodologies outlined in this compendium can be used to guide the estimation of GHG emissions for individual projects, entire facilities or company-wide inventories. The methodologies focus on estimating CO 2 and CH 4 emissions from oil and gas industry operations. Carbon dioxide and methane were selected because they are the most relevant potential GHG compounds to the oil and gas industry. Other compounds may require evaluation for specific, non-traditional operations, or as new data become available.

The emission estimation approaches presented are practical for all segments of the oil and gas industry. Operations and facilities addressed range from the well-head to retail outlets, including exploration and production (E & P), refining, marine vessels, pipelines, bulk distribution, and other transportation, and retail marketing. The methods presented in this compendium pertain only to emissions from operations and not those that might be attributable to product use. Industry data provided throughout this document list the carbon content fraction for typical fuels in commerce, but no attempt is made to account for hypothetical efficiencies associated with products use.

It is important to note that prior to applying thse methodologies and developing any inventory, careful consideration should be given to the scope and boundaries for the estimate, per company policy and its needs. Careful documentation of decisions made and boundaries for the inventory being created will help avoid duplication, redundancy, or other problems with the final estimate. Moreover, the dynamic nature of oil and gas industry operations, along with changes in estimation procedures, necessitate good narrative descriptions of operations and equipment included, in addition to careful calculations and knowledge of operating procedures.