CNG injection skids: connecting stranded gas to the national grid

As the national pipeline network is knitted into a single grid, more stranded supplies are injected as CNG. That opens an economical route to market for associated gas around oil fields, coal-bed methane and shale pilot production, and it creates a new duty for CNG pressure-reducing skids.

In November 2025 the National Development and Reform Commission issued the revised Measures for the Planning, Construction and Operation of Oil and Gas Infrastructure, effective 1 January 2026. The policy encourages social capital to take part in non-trunk pipeline facilities and supports joint construction, while setting the well-known 5 % storage obligations for suppliers, PipeChina and city-gas companies, plus five days of emergency storage for local governments. The direction is large hubs, clustered siting, joint build and lease-or-buy, with scattered small storage discouraged — stranded gas is expected to enter the grid in a regulated, clustered way.

Stranded sources include associated gas, coal-bed methane, shale pilot gas and remote well gas. Without grid access, such gas is usually flared or used inefficiently. The CNG route is: treat, compress to CNG, haul to the injection point, then let the reducing skid put it into the pipeline.

The skid takes high-pressure gas delivered by tube trailer, typically 20–25 MPa, and reduces it to grid pressure. Compared with an ordinary CNG reducing skid, injection duty demands higher stability, continuous operation and safety redundancy. Two-stage reduction with one duty and one standby line is the usual arrangement: the first stage drops 20–25 MPa to 2.0–3.0 MPa, the second to 0.2–0.4 MPa or whatever the grid requires. Two stages cut the pressure ratio per valve, which avoids seat erosion and hydrate or ice blockage; the duty/standby pair lets one line be serviced while the other carries the load without interruption.

The engineering difficulty is heat exchange and frost protection. Reducing high-pressure gas absorbs a great deal of heat and the gas temperature can plunge below −30 °C; without adequate heat the line frosts or plugs. Skids are configured to site conditions: electric heating where no hot water exists, hot water from a boiler or waste heat, or steam where the plant has a steam source. Outlet temperature is usually held above 5 °C so downstream piping never freezes.

Take the March 2026 specification from Tengzhou China Resources Gas as a working example: single inlet, one duty plus one standby, each line independent, two-stage regulation, electric heating, 1000 Nm³/h per line, outlet 0.3–0.4 MPa. That combination is typical of injection and single-point supply projects.