The origin of the world’s mineral resources lies deep within the earth. Source rock – rock in which hydrocarbons are capable of being generated – formed both on land (continental source rock) and at sea (marine source rock). Huge quantities of plant and animal life sink to the sea bed – while on land, vast amounts of dead vegetation accumulate in swamps, moors, and on rainforest floors. High temperatures, bacteria, and extreme pressure caused the organic sediment to turn into source rock.

When the source rock has reached a certain maturity, its lighter contents rise. Because crude oil and natural gas have lower density than water, they are pressed up out of the source rock. For crude oil, that happens at depths of less than two kilometres – and for natural gas, more than three kilometres below the surface.

The valuable hydrocarbons are then trapped in natural oil and gas folds – named reservoir rock – that form when porous sandstone or limestone bulges out above the source rock and is capped by impervious rock layers such as salt or clay.

Natural gas or crude oil deposits require the following to exist:

— Source rock that has collected and released hydrocarbons

— Reservoir rock that stores oil and gas in its pores and can release it when drilled into

— Cap rock that completely seals the deposit from above

— The formation of geometric traps in reservoir and cap rock – also referred to as structures – that trap the hydrocarbons