Issues & Design Trends In Onshore Gas Reception Facilities

Abstract

Abstract In pursuit of greater safety, lower environmental impact and lower capital expenditure, it is desired to reduce (or preferably eliminate) upstream offshore processing. Specifically for offshore platforms, the biggest capital expenditure savings can be achieved by either designing the offshore production facilities to be unmanned platforms or having subsea completions without a platform. In both cases all produced wellhead fluids will need to be transported untreated to shore in trunklines. A major contributor to HSE incidents in the upstream oil and gas industry is the logistics of bringing people to and from the platforms by boat or helicopter transport. Being able to avoid the necessity of this people transport will greatly improve the overall safety performance of the gas production. Furthermore, zero-effluent discharge offshore can be achieved by sending all of the produced fluids to the onshore plant for processing and disposal, as an alternative to the standard offshore processing and reinjection. A further trend in recent developments is that of poorer-quality feedstock gas. Amongst others gas is becoming more sour, containing up to 40% H2S and up to 70% CO2. This, coupled with the elimination of offshore processing facilities requires the injection of chemicals to combat trunkline corrosion and formation of hydrates. The higher quantities of acid gases, free water (condensed and formation water), injected chemicals and increased corrosion products all have to be handled by the onshore gas-reception facilities that have to produce acceptable quality gas for the downstream facilities. The onshore facilities also have to be robust for transient conditions like receiving significant slugs of production water during pigging and start up. As the gas and condensate specifications are getting more and more stringent stable operation of the units downstream the slugcatcher is essential to ensure on specification products. To realize this the downstream condensate stabiliser train needs a continuous feed of condensate even when water slugs enter the slugcatcher. Furthermore, potential water breakthrough to the condensate stabiliser train brings challenges to the design of the stabiliser column. These trends require the onshore gas-reception facilities to do more, and in more difficult circumstances. This in turn is leading to more complex gas-receiving facilities and an increase in the unit's cost. As the experience with the onshore gas-receiving facilities without offshore platform is still building up, it is essential that sufficient time and effort is spent in the design phase to identify the possible risks and challenges.