The Role of Gas Processing in the Natural-Gas Value Chain

Abstract

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Abstract Production of natural gas is the first step in the value chain that takes gas from the reservoir to the customer (typically at a burner-tip). An integral and essential part of this value chain is the midstream sector. Midstream refers to the gathering, compression, and processing functions required between the wellhead and the transmission system. Midstream assets and activities are found at any location where natural gas is produced, transported, or sold. For example, in North America the first gas-gathering and -processing facilities were installed circa 1910, primarily to extract casinghead gasoline from solution gas produced with crude oil. In Europe, the midstream sector developed in the 1960s with the discovery of large nonassociated-gas fields in the southern North Sea and in the Groningen field in The Netherlands. Industry development in the Middle East was spurred by the huge associated-gas-gathering and -processing projects initiated by Saudi Aramco in the late 1970s and early 1980s. Fig. 1 shows a schematic of the gas-gathering and -processing facilities in the total production system. This article discusses the gas-processing portion of the midstream sector, with the primary objective of providing technical professionals on the upstream side of the industry some insight into the midstream sector. Gas Conditioning and Sales-Gas Specifications One of the principal objectives of the gas-processing industry is to condition the gas for sale. Natural gas must meet several specifications before it can enter the transmission system. Historically, these specifications have been referred to as "sales-gas specifications," but in many areas they are really transportation specifications. This is because gas from many producers will be transported in "open-access" gas pipelines to the gas buyers along the pipe route. The sales agreement may be between the producer and the buyer, but there is no guarantee the buyer will actually receive the producer's molecules. In North America, for example, producers negotiate transportation agreements with pipelines and must meet the shipper's transportation specifications before the pipeline operator will accept the gas. These specifications are set out in the tariff the shipper files with the US Federal Energy Regulatory Commission. Table 1 shows some example sales/ transportation specifications in North America and Europe.