Gas hydrate problem in Oil and Gas Wells Petroleum Engineering Problems in Wellbore Gas hydrate prevention

1. Gas Hydrates Problems
in
Oil and Gas Wells

2.  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.

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

5.  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)

7. 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

8. 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.

9.  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.

10.  “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 theTransformer.

11.  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.

12.  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.