The benefits of geographic information system (GIS) technology in the oil and gas industry are well understood, especially in the local distribution network. GIS technology has served as a valuable tool for the efficient and effective management of assets in the industry for many years. From a cartographic and geospatial data perspective, three major structural differences distinguish the corridor- mapping projects performed for gas and oil pipeline companies from traditional mapping projects performed for local gas distribution companies, municipalities and counties, telephone and utility companies and most other private sector companies. The first difference is the geometry of the network. The second difference is the need to support remote or long-distance design, monitoring and maintenance activities. The third difference is the need to accommodate often extremely variable terrain conditions and accessibility issues during base-map data collection. These differences, which affect the definition and development of appropriate GIS, are the focus of this article.
Network Geometry
Traditionally, local service companies have concentrated their efforts on the provision of services within relatively small, contiguous service areas. Even in situations where the corporate entity provided service over a large geographic area, the territory was typically contiguous and subdivided to facilitate local support and logistics.
In contrast, corridor-based transmission networks are essentially concerned with point-to-point linkages over great physical distances. For engineering design purposes, such a network can be thought of as one-dimensional. The basic work unit is a line or link (the pipeline) connecting nodes such as compressor stations.
One significant result of this difference is the area covered by a basic work unit and therefore the method of organising data and contracting for engineering and data conversion services. Another result is reflected in the arrangement and number of maps required for graphic display. A typical local service gas company in the US might serve an area of 15km by 20km in extent, or approximately 300km2. The GIS for this typical service area might use maps that are 500m (north to south) by 1,000m (east to west). Therefore, approximately 600 maps would be required to provide complete coverage.
The basic work unit for a corridor-based transmission company is the backbone project, which defines a link between two major sites (and, perhaps, intermediate stations). A typical work unit might be a line of 1,200km (or more) in length and from 1–3m wide. The as-built records will provide information only for a narrow swath, perhaps 50m wide, of the project’s total length. Therefore, the mapping area covered by this work unit would be, in aggregate, only a few dozen square kilometres. However, because this area might extend more than 1,200km, at least 1,200 digital maps (500m by 1,000m) would be needed for complete coverage.
The phrase ‘at least’ is an important qualifier. If the local service company approach of panelling maps together is used by a corridor-based transmission company, and if the 1,200km route runs straight east to west, 1,200 maps would suffice. If the route runs straight north to south, 2,400 maps would be needed. If the route was markedly sinuous, an even larger number of maps might be needed.
At this point, an objection might be raised that panelling in this manner is not an efficient way to map corridor-based transmission company facilities. Although this is an option in some circumstances, there are two fundamental reasons for retaining the panelling approach. First, corridor-based transmission company systems often exhibit a pattern of irregular growth (at least in terms of ancillary or secondary routes), and the jigsaw puzzle-like network continues to become more complex. Provision must be made in many cases for the addition of new route information in some coherent and rational manner. The same would be true in the case of asset acquisition or the management of multiple routes by a single owner. The integration of geo-referenced third-party databases is accommodated most easily bybuilding the system using a regular geographic co-ordinate system and grid. This is particularly important if secondary uses such as the addition of fibre optic cables to pipeline corridors are anticipated. Regardless of the approach to tiling, the question of tile configuration must be explicitly considered for corridor-mapping.
Given the theoretical length of the project, the GIS designer must also consider the probability that the project will cross one or more central meridians (longitude origins) for a given projection and co-ordinate system, requiring calculation of dual co-ordinates near that line of longitude to accommodate multiple co-ordinate systems or zones.
Category:
Transportation
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