Global Greenhouse-Gas-Emissions Inventory Method
Authors: Schievelbein Vernon , Lee Arthur 
Published: June 2014

This paper (SPE 57080) was revised for publication from paper SPE 52672, originally presented at the 1999 SPE/EPA Exploration and Production Environmental Conference held in Austin, Texas, 28 February–3 March. Original manuscript received 13 January 1999. This paper has not been peer reviewed.

Summary
An emissions inventory is a powerful, multipurpose tool used by regulators, public-interest groups, and other stakeholders in the environmental protection arena. Given the growing conviction that market-based approaches are more effective than command-and-control regulations, inventories will increasingly be used to influence the behavior of companies in the marketplace. Carbon dioxide (CO2) and other greenhouse-gas (GHG) emissions are becoming important elements in the emissions inventory. Under the Framework Convention for Climate Change and now the Kyoto Protocol, emissions inventory of nations, as well as of the regulated community, will come under additional scrutiny when emissions targets and timetables have to be met once the protocol is put in place.
Data accuracy and consistency and the cost and timing of delivery of data from Texaco's worldwide business units (BU's) were important considerations in the selection of the company's emissions inventory method. This method is based primarily on the coupling of emissions factors with fuel or product throughput or with equipment-component count. The emissions source list is comprehensive, and, in some cases, the emissions factors used are based on more recent source measurements with greater accuracy. This paper describes the basis for generation of a worldwide emissions inventory for the company.

Introduction
In 1998, Texaco Inc. decided to inventory the 1997 GHG emissions that come from its worldwide operations. The purpose of the inventory is to provide data for GHG-emissions management and for participation in the ongoing GHG dialogue. The company took the following steps to complete the inventory.Management announced a corporate goal to complete the inventory in 1998 and commissioned an emissions inventory team for this inventory collection. The team included representatives from the Health, Safety, and Environmental (HSE) staff of the BU's; from technology and general engineering centers; from the corporate center; and from among other BU staff.The emissions inventory team prepared a guidance document that defined the scope and method for the inventory. A subteam created the questionnaire that was completed by the operating units within the BU's.The questionnaire was completed on schedule, with coordination, follow-up, and verification provided by BU HSE offices.The data from the BU's were compiled and organized by the inventory team to complete the corporate emissions inventory.
The inventory team realized that issues regarding the scope of the inventory and choice of method needed resolution before the inventory could be completed. The issues at stake included inventory cost and reliability and data comparability and consistency within the company and over extended time frames. There was a need for agreement within the company before the BU's were asked to supply data or information necessary to do the companywide inventory. We had to be certain that the BU's were capable of supplying data within the time frame allotted for data collection. The inventory team considered these issues and formalized the conclusions into the Texaco Emissions Inventory Document. The method detailed in this document is summarized in this paper.

Principles to Ensure Usefulness of Inventory Data

Comparability and Consistency.
The inventory method addresses oil and gas fields, refineries, oil and gas pipelines, gas plants, and petroleum-product marketing operations in many countries and from offshore operations. It also addresses emissions from joint ventures, including those that are operated by other companies and those that are the operating company for assets that are partially owned by other companies. Texaco's operations are operated with a high degree of autonomy by BU's, which have their own HSE organizations and generally manage their environmental issues to meet local environmental concerns and regulations. In consideration of cost and time, the BU's supplied data for the inventory that were already available or that could be obtained quickly. The guidance document stressed consistent emission factors for determining emissions across our companywide business segments.
We needed to achieve comparability in the inventory that would allow quantitative assessment of the similarities and differences among different facilities and different sectors of the company. In addition, consistency was needed to allow comparison over time of information from the same facility, same sector, and even the company itself. Because the company plans to grow its business, correlation of product-production rate with GHG-emission rates was stressed.
In areas of the world where environmental regulations are relatively mature, much of the data needed for the inventory data already existed in databases of operating units. These data typically would be obtained by methods that satisfied state or local regulatory agency requirements. For other segments of our company and in other parts of the world, emission data were either not available or not readily available.