A lot of exaggerated nonsense in blogs on the raddio.
Seismicity is used to find likely oil and gas traps in the subsurface. "Highs" or blockages to trap hydrocarbons in porous sediments are two anomalies sought by petroleum explorationists, and become prospects.
The hydrocarbons encountered vary, depending on the thermal history.
The hyrdocarbons in sediments undergo a natural 'cracking' depending on the heat and pressure on the formation. Very heavy hydrocarbon molecules are separated, lighter fluids and gases are generated that can be extracted through the well bore. If thermal effects are very strong, the result is more gas and less or no liquid hydrocarbons.
The formation being explored at the Macondo well has a strong gas element, but liquid hydrocarbons are also present; contributing to a desirable crude. Gases have become an important contributor to our energy needs.
Of course if the formation is breached, the gas pressure will force both liquid and gaseous materials to the surface, usually confined and prepared for production.
Unfortunately, mistakes and unpreparedness led to the gusher at Macondo being uncontrolable.

Nonsense about eventual collapse and tsunami belongs in children's science fiction comics. Of course the disaster is catastrophic enough without such laughable speculation.

Hydrocarbon gases normally are a mixture of the lightest hydrocarbons, methane to ethane and etc.; there is nothing unusual about that. In some regions subjected to stronger thermal effects, the gases approach the very light end, methane.
Along with the hydrocarbon gases, many crudes contain sulfurous gases and compounds. There is a good market for sulfur at present, but I remember seeing large piles of extracted sulfur near some refineries.
All of these gases are toxic, the degree depending on the type and concentration. Care must be taken in handling them. Crude oil itself is not the friendliest of substances.