To control inlet pressure on devices, such as separators, treaters, and heaters, system designers use regulators. The purpose of this application guide is to familiarize you with the common product applications in the oil and gas industry

Types of Regulators

The regulators used in the oil and gas industry fall into three categories: pressure reducing, differential/bias, or relief backpressure.

Pressure Reducing Regulators

In some applications, the pressure may need to be reduced for a process or equipment. Depending upon the accuracy required by the application, a direct-operated or pilot-operated regulator can be used to reduce the fluid pressure.

Direct-operated regulators are used for lower flow rates. Pilot-operated regulators are used for high flow rates or where precise pressure control is required.

Differential/Bias Regulators

A differential or bias regulator maintains a pressure difference between two locations in the system.

Relief Valves/Backpressure Regulators

A relief valve or backpressure regulator opens when the upstream controlled pressure increases above the setpoint. Relief valves and backpressure regulators are the same devices. The name is determined by the application.

Overpressure protection is provided by relieving pressure when it rises above the setpoint. When upstream pressure rises above the setpoint, the relief/backpressure regulator opens to allow excess upstream pressure to flow downstream, typically into a pressurized system or to atmosphere.

Oil and Gas Applications

Applications for Emerson Regulators

Emerson regulators are used throughout the oil and gas production industry. Following is a list of the common applications and the regulators used for each application:

Fuel gas for heaters and separators - Types 630, 627, 99, 66, 64, and Y690A

Fuel gas for compressors and turbines - Types 310A and 99

Thermal injection recovery - Types 95, 98, and 63EG-98HM

Gas gathering - Types 630 and 627

Utilization - Type Y690A

Farm taps - Types 630 and 627

Pump recirculation - Types 98 and 63EG-98HM

Lubrication systems - Types 98 and 63EG-98HM

Underground gas storage - Types EZR, 399A and 310A

Instrument supply - Types 1305, 1367, 1301, 64, and 67

Dump valve - Type 119

General pressure reduction applications - Types 630, 627, 95, Y690A, 1098-EGR, EZR and 99

General relief/backpressure applications - Types 98, H120, H200, 414, 1805, 289, 63EG, 630R, EZR, and EZR LD

Secondary Oil Recovery Methods

A reservoir may approach the end of its primary life having produced only a small fraction of the oil in place. Even when using the best primary production methods, much of the oil may be left behind. To recover this oil, secondary recovery methods are used.

A common secondary recovery method is thermal injection. Thermal injection recovery methods lower the viscosity of oil and increase its flow by introducing heat (steam or hot water) into a reservoir. High-viscosity and high-density crude oil responds better to heat applications than to other recovery methods. The steam or hot water is pumped into the injection wells and moved toward the producing wells.

Separation

Producing wells contain a wide variety of complex fluids, including unwanted impurities. These fluids and impurities are separated prior to further processing.

A well stream separator divides the liquid hydrocarbons from the gas. Through the use of level and pressure control instrumentation, regulators, and control valves, the separated gases and liquids are discharged from the separator.

Treating

Treating is another method of removing any water that remains in the liquid hydrocarbon. This water is considered to be in an emulsified state. The specific treating method is determined by the characteristic of the emulsion. Chemical treatment, mechanical extraction, and heating are common methods of treating.

Chemical Treating and Filtering

The introduction of chemicals into the flowing stream weakens the film surrounding the water droplets. Some form of mechanical extraction is typically used to remove the droplets from the well stream.

Mechanical Extraction

Mechanical extraction filter beds, baffles, or mist extractors provide surface areas on which the water droplets can collect.

Line Heating

Heat increases the effectiveness of a chemical on an emulsion, and reduces the viscosity of the oil-water emulsion making it easier for the water droplets to be separated.

 

 

The heating of a well stream can be accomplished directly or indirectly. Indirect line heaters transfer heat to the process stream through a heat transfer media (bath). Direct-fired line heaters are those in which the heat is transferred to the flow stream without the use of a media (See Figure 3).

 

 

Heater Treaters

The majority of emulsion treating used in the oil industry combines heating, mechanical extraction, and settling. Heater treaters were developed as a logical integration of these three emulsion-treating processes.

Hydrate Formation

Most natural gas contains water vapor, and if it cools below a certain temperature hydrates can form. A hydrate is a solid compound formed by hydrocarbons and water that forms under certain pipeline conditions. Hydrates may pack solidly in gathering lines, regulators, and control valves, blocking the flow of gas.

Hydrate formation can be prevented by: heating the gas, injecting chemical inhibitors, and dehydrating the gas

Sweetening

Often natural gas needs to be "sweetened." A gas or crude is termed "sweet" if the hydrogen sulfide (H2S) or carbon dioxide (CO2), or both, have been removed from the well stream to levels below industry limits. A gas or crude that remains contaminated with H2S or CO2 is called "sour". Sour gas can cause damage to equipment, such as sulfide stress cracking. When selecting regulators for use on sour gas, always choose the NACE options. Wetted parts are made of special materials to comply with NACE standards.

Sulfide Stress Cracking (SSC)

H2S does not actively participate in the SSC reaction, but sulfides act to promote the entry of the hydrogen atoms into the base material. While most molecules will eventually collect, form hydrogen bubbles, and float away harmlessly, a percentage of the hydrogen atoms will diffuse into the base metal and embrittle the crystalline structure to failure.

NACE (MR0175)

The NACE Standard MR0175, "Sulfide Stress Corrosion Cracking Resistant Metallic Materials for Oil Field Equipment" is widely used throughout the world, specifying the proper materials to provide good service life in sour gas and oil environments. NACE (National Association of Corrosion Engineers) is a worldwide technical organization which studies various aspects of corrosion and the damage that may result in refineries, chemical plants, water systems, and other types of industrial equipment.

The Regulator

The MR0175 Standard requires the use of double heat-treated cast steel castings. No special treatment is required for CF8M stainless steel castings. Emerson Process Management Regulator Technologies offers several regulators made from WCC steel or WCB steel and CF8M stainless steel which are compliant with NACE standards.

The MR0175 Standard does allow the use of aluminum-base alloys. However, the user is cautioned that corrosion may be excessive.

MR0175 does not allow the use of cast iron for a pressure containing part because of low ductility. Also, cast iron cannot be used in a non-pressure containing part without approval of the purchaser. For this reason, Emerson Process Management Regulator Technologies does not provide cast iron regulators for sour gas service.

The Spring

If a regulator spring used for sour gas service is a wetted part, it must be NACE compatible. This presents a problem because springs must have high strength (hardness) to function properly. Typically, Inconel X750 springs are used for sour gas service.

Gas Gathering

After the natural gas is separated and treated, it is brought together in gathering lines. These gathering lines join the gas from several production sites. The gathering lines meet at a field compressor. Gas enters the compressor at 30 to 60 psig (2,1 to 4,1 bar) and is compressed for transmission.

Utilization

Field gas is piped from the compressor back to the production site. This gas is used as fuel gas for separators and treaters, for heating and injection systems, and for on-site utilization.

This gas can also be utilized by isolated farms or lodges along the pipeline. This application is typically called a field or farm tap.