Hydrocarbon Reservoir

A hydrocarbon reservoir is a subsurface natural storage of hydrocarbon fluids such as crude oil and natural gas. Generally, these natural storages are sedimentary rocks like sandstone or limestone. In rare occasions, igneous rocks like granite can also store hydrocarbon naturally in some very special conditions.

In order to form a hydrocarbon reservoir, 3 basic conditions must fulfilled:

1. Presence of "Source Rock". A source where hydrocarbon formed in the vicinity of the reservoir.
2. Presence of "Cap Rock". These must be a "cap" or impermeable rock to prevent the hydrocarbon from escaping.
3. Presence of porous medium. For the hydrocarbon to reside, the reservoir rock must contain empty spaces called pore spaces. These may be in-matrix pores or fractures.