Laboratory tests and field implementation of gas-drag-reduction chemicals

Abstract

Drag reduction in gas-transmission lines can be achieved by applying a thin chemical coating on the pipe inner surface to reduce friction between the flowing gas and pipe wall. Newly identified molecules used for gas-drag reduction can strongly bond to metal surfaces and form a smooth film to mitigate gas turbulence at the gas/solid interface. Effective gas-drag reducers have properties similar to corrosion inhibitors and lubricants or a combination of both. Fatty acids, oxylated fatty acid amines, and/or amides with carbon numbers between 18 and 54 can provide this type of behavior.1 The desired scenario is based on positively charged amine and amide functional groups providing strong binding to the metal surface and the long-chain hydrocarbon part serving as a compliant or lubricating surface to mitigate turbulence at the gas-phase boundary.2 A field test using Nalco 945 corrosion inhibitor at High Island 24L [a 7.625-in. inside diameter (ID) and 6.25-mile-long gas line from an offshore platform to the inland facilities in Sabine Pass, Texas] demonstrated gas-throughput improvement up to 20% at its peak performance. The improvement can be defined either as a reduction in pressure drop at a constant flow or as a flow-rate increase at a constant pressure drop. In this case, the gas-drag reducer resulted in a decrease in pressure drop from 180 to 150 psi and an increase in flow rate from 50 to 52 MMscf/D, while maintaining discharge pressure at about 840 psi. Its effectiveness peaked at the third week after one injection treatment, and then gradually tapered off. Benefits lasted more than 2 months.