When people talk about "Energy Security" they are usually referring to the energy supply to the west. Most of the finite fossil fuels are owned by Nation States, ie they are nationalised. About 80% of all oil is nationalised. And most of those nations are not in the west.
Many people in the west fear that Europe will become too dependent on Russian or Middle East oil and gas, and that competition to secure new sources of oil could lead to conflict.
The "Great Game" describes the way Russia uses its energy policy to exert influence over its neighbours in the Caucasus or central Asia.
The "Scramble for Africa" refers to the west's competition with China over oil investments in Africa.
Many of the nation states with large supplies of oil are weak and/or authoritarian. This stems form the fact that these states do not have to rely on taxes to run the government. Reliance on taxes requires the cooperationof the populace.
Reliance on oil means the government does not have to listen to their people.- they do not have to have a "social contract with their citizens". These states are called "Rentier" as they rely on oil rents. It seems that oil rentiers are associated with voilent conduct. Pipelines are blown up, oil workers are taken hostage, smuggling and corruption are widespread in places like Iraq, Chechnya, Nigeria, or Columbia.
In many of these countries, there are both legal networks receiving oil rents, but also illegal and patronage networks.
Sudan is an example of a weak country, dependent on the oil rents. While the then UK Foreign Secretary, Margaret Beckitt claimed the war Darfur is down to climate change reducing resources thus increasing competition within the region. She didn't mention the competetion between west and China to capture these oil assets excerbates the system. More on Darfur, China & Oil from Human Rights Watch
One country that does not have nationalised oil any more is Iraq. One of the first Acts to be bought in by the new government in Iraq was the Hydrocarbon law, designed to allow local politicians to negotiate with external oil companies. This replaces the nationalised system that Saddam Hussain had introduced.