Presented By:Himanshu Rajawat (12/396)

Gas Hydrates Problems in

Oil and Gas Wells

Gas Hydrates:

Gas Hydrates are crystalline water based solids physically resembling ice, in which small non-polar molecules (typically gas) or polar molecules are trapped inside “cages” of hydrogen bonded, frozen water molecules.

Other names are gas clathrates, clathrates, hydrates, etc.

Simply, Gas Hydrates are clathrate compounds in which the host molecule is water and the guest molecule is typically a gas or liquid.

Most low molecular weight gases, including O2, H2, N2, CO2, CH4, H2S, Ar and Kr.

Necessary Conditions:

The necessary conditions: - Presence of water or ice - Suitable sized gas/liquid molecules ( Such as C1, C2, C3, C4, CO2, N2, H2S etc.) - Suitable Temperature and Pressure conditions. - Temperature and pressure condition is a function of gas/liquid and water composition. (Generally High pressure and low temperature)

Gas Hydrates At the appropriate combination of temperature,

pressure and low-molecular-weight-gases, water molecules arrange themselves into co-planar 5- or 6- membered rings which then form three dimensional (3D) polyhedra around the gases

The temperature at which the gas hydrates are formed is higher than the temperature at which ice forms.

The exact PT conditions for equilibrium vary with hydrocarbon-gas-composition and the dissolved salt contents in liquid water phase.

(Generally salt wil control the chemical activity of water from which the hydrate forms)

General Phase Diagram of Hydrates

1. hydrates+gaseous hydrocarbon (+excess liquid water)

2. Hydrates+liquid hydrocarbon (+excess liquid water)

3. Ice+gaseous hydrocarbon

4. Liquid water+gaseous hydrocarbon

5. Liquid water+liquid hydrocarbon

Prevention of Hydrate Formation

1.) By the use of model The first step in controlling hydrate formation is

to know the pressure and temperature conditions in the well by PVT simulators.

The second step is to compare this information to measured PT profile within the producing system.

Prevention of Hydrate Formation The alternative of prevention is to use INHIBITORS These are classified as: 1. Environmental Inhibitors 2. Thermodynamic Inhibitors 3. Kinetic Inhibitors

“Environment inhibition” method is to dry the gas before it is cooled. Remove the water and hydrates so they can not form.

This involves adsoption onto silica gel, absoption of water into alcohol, adsorption onto hydroscopic salt.

Prevention of Hydrate Formation “Thermodynamic Inhibition” has

been the most common method for controlling gas hydrates.

These are : heating the gas, decreasing pressure in the system, injecting salt solution, and injecting alcohol or glycol.

The use of electrical-resistance heating via cables connected to the Transformer.

Prevention of Hydrate Formation Injection of salt (generally CaCl2)

reduces the hydrates formation by lowering the chemical activity of water, and by lowering the solubility of gas in the water.

Removal of Solid Hydrates Solid hydrates are removed with many of the

same chemicals and technology used in inhibition of hydrate formation. The simplest method is, if possible, to reduce the pressure above hydrate plug sufficiently enough to reverse the equilibrium reaction. Addition of solvents, such as alcohols and glycols, is the most common technique. Hydrate plug removal with coiled tubing jetting technique. Chemical heating such as wax.