Flow Assurance/Natural Gas Dewatering

The Hydrate Asymmetric Restraint Technology (HART™) water extraction for flow assurance project concerns dehumidifying natural gas through the formation of hydrate masses on porous restraints, functioning as sophisticated heat exchangers. This technology has the potential to prevent the formation of unwanted hydrate within natural gas pipelines near the wellhead without the use of chemicals.  The energy costs are very low and the process is environmentally friendly.  The HART™ flow assurance system is comprised of modular units that can be inserted into an existing pipeline system or placed within process manifolds or shunt systems. 

Gas and oil fields in the Gulf of Mexico have moved from shallow water where drilling and production platforms could be almost co-located to progressively further offshore and into deeper water.  Deep-water fields may be over 25 miles from production platforms located in shallow water.  As the pipelines get longer and the bottom waters progressively colder as deeper water wellheads are opened up, the flow assurance problem of unwanted natural gas hydrate formation is becoming acute.  Other deep-water areas are also encountering increasingly difficult to deal with unwanted hydrate formation.

(image courtesy of the Minerals Management Service)

Unwanted hydrate forms when hot, water-saturated gas is extracted from its geological trap and transmitted through seafloor pipelines.  The problem is particularly acute where reservoir pressures are high and where seafloor temperatures are very cold.  The cold water cools the pipeline, which in turn cools the gas and drives the dissolved water into super-saturation. In these conditions of supercooling, unwanted hydrate will form from the hydrate forming natural gases and the dissolved water.

At present, thermodynamic and kinetic inhibitors are used to retard the formation of hydrate.  Conventional inhibition is expensive and its usefulness is limited in many deepwater energy sites.  HART™ approaches the unwanted hydrate problem differently. HART™ reduces the concentration of water in the gas so unwanted hydrate will not form, no matter how long the transmission system distance or residence time in the transmission system. The water entrapped within the hydrate that is formed on the porous restraint is removed from the pipeline system and gas is returned to the system.  The technology does not require adding any chemicals such as methanol, glycol or LDHI.  Energy requirements are low, especially where the method can be implemented at or near the wellhead in deep water, utilizing the cold water to chill the restraint.