Crude Oil Wellhead and Battery

Most of my experience is on major oil and gas plants even complexes, which are more downstream. From June 2010 to Feb. 2011, I worked for Vantage Engineering Inc., a smaller size EP&C company. It focuses on wellheads and batteries. Although the piping itself was simple, it gave me a chance to explore the upstream sector of the industry.

Figure 1, explains the routes oil and gas brought from underground to final users. Starting from a reservoir, oil or gas is extracted to the surface through wellhead. This leads to a processing facility, storage depot and/or other pipeline eventually leading to a refinery or distribution center (for gas). For oil sands, the extraction methods are different. I’ll discuss them in later posts.

 

Fig. 1 Oil and Gas Processing Block Diagram

What is a wellhead?

When a well is drilled on land, an interface is required between the individual casing strings and surface facilities. Wellhead provides suspending point for the casing strings running through the wellbore and also acts to contain the pressure inside the casing strings.

There are two categories of surface wellhead systems: onshore and offshore.

                    Fig. 2 Wellhead & Christmas Tree Components

Wellhead also provides means for attaching a Christmas tree for production operations. Christmas tree is equipped with set of isolation and choke valves and serves for pressure control. When the well and facilities are ready to produce and receive oil or gas, tree valves are opened and the formation fluids are allowed to go through a flow line.

The typical wellhead piping I did including block valves, pressure gauges and a pressure control valve. Before the pipe goes underground, a pig launcher is always installed for maintenance.

What is a battery?

Prior to delivery to market or other disposition, oil and gas normally need to be preliminarily processed. For example, heavy crude when first produced can have high levels of impurities such as 5+% sand and 30+% water. The total of these two must be reduced below 0.5%.  As well, the viscosity must often be decreased so it will flow.  The battery is where the cleaning and "treating" occurs. 

Fig. 3 Wellhead and Battery before pipeline

A battery is an upstream facility in an oil or natural gas field that collects raw oil or natural gas from one or more wells. Depends on for oil or gas and their quality, battery includes equipment for measurement, for separating inlet streams into oil, gas, and/or water phases, for cleaning and treating the oil, for disposal of the water, and for conservation of the produced gas. A tank battery may include a glycol dehydration unit and compressor.

After all these treatments, oil and gas are ready to be gathered into a pipeline for downstream process.