Historically, Saudi Arabia's natural gas resources have taken a backseat to oil. Associated gas in produced oil was seen as an unwanted by-product and flared. As oil reservoir pressures declined, Aramco experimented with re-injecting this gas to maintain pressure, but this method was soon replaced with water injection to maintain pressure. In 1975 work started to create the Master Gas System (MGS) — a system of gas gathering facilities and pipelines networks — that would process the associated gas to produce sales gas (almost pure methane), ethane for feedstock, Natural Gas Liquids (NGL), sulphur and transport the end product to customers. As the need for domestic use of natural gas demand grew, additional facilities were added to the MGS to extract, process, and deliver sales gas, ethane and NGL to customers. Presently, sales gas is produced in six gas processing facilities. In addition, an NGL recovery plant ("straddle plant") extracts higher order gas fractions and NGLs from rich gas streams and injects lean gas (methane) back into the MGS. The sales gas is transported through a number of large diameter pipelines (36-inch to 56-inch) along the Eastern region and out to the Central (Riyadh area) and Western regions of Saudi Arabia. Gas demand can drive the capacity of the MGS to its limits. It exceeds 7 bcfd during the summer months as an aggregate and can go much higher on an instantaneous rate basis. This paper will present the new pipeline management tool ("MGS-STAT") and will outline how this tool meets the specific requirements for operating this unique system, such as online survival time predictions, optimizing rich gas injection to meet demand and contractual pressures, and minimize associated costs. The paper will present in detail the implementation procedure, hydraulic design, communication architecture, maintenance process, optimization process, challenges faced and results of the implementation of the pipeline management tool.
Crude oil from various oil wells is fed through flow lines to gas/oil separation plants (GOSPs). At the GOSP, associated gases, oil and water are separated with the gas sent to gas processing plants, oil to crude stabilization units and then onwards to refineries and tank farms. Gas from the crude stabilization units are sent to gas processing plants. Non-associated gases from gas fields (from the Khuff reservoir) are also sent to the gas processing plant for processing. The products from gas plants include sales quality natural gas for domestic end users, Natural Gas Liquids (NGL) for fractionation, and ethane for feedstock. Most of the gas processing plants are in Saudi Arabia's Eastern Province west of the Arabian Gulf. On the southern end the Haradh Gas Plant ("HdGP") and the Hawiyah Gas Plant ("HGP") process nonassociated gas and feed sales gas to the pipeline network. Large diameter pipelines then take this gas to a "straddle plant" known as the Hawiyah NGL Recovery Plant ("HNGL") where the heavy constituents of the sales gas are extracted to produce NGL and lean gas is fed back into the grid.
