Petroleum reservoir

A subsurface body of porous, permeable rock containing hydrocarbons that can flow to wells. Its ability to store and transmit fluids depends on pore structure, pressure, and geological confinement.

Porosity: The fraction of a rock's bulk volume occupied by pores or voids. Pore volume determines how much petroleum the reservoir rock can store.
Sedimentary rock: Rock formed from deposited sediment, chemical precipitation, or accumulated organic material. Most petroleum reservoirs occur in sedimentary formations shaped by burial and deposition.
Reservoir engineering: The discipline that analyzes subsurface fluid flow to plan and optimize hydrocarbon production. It uses reservoir properties and pressure data to design production strategies.
Petroleum source rock: A hydrocarbon-generating rock in which organic matter has been transformed into oil or gas. Unlike a reservoir, it generates petroleum and need not transmit it to wells.
Permeability: A measure of how readily fluids pass through connected spaces in a material. Connected pores let hydrocarbons flow through the reservoir toward wells.
Source rock: A rock containing organic matter capable of generating oil or natural gas under heat and pressure. It supplies hydrocarbons that can migrate into a separate reservoir.
Well logging: Measurements made in or near a borehole to characterize surrounding rock and fluids. Logs help estimate porosity, fluid content, and rock boundaries in a reservoir.
Tight oil: Crude oil held in low-permeability rock that generally requires stimulation for commercial production. Its host rock resists ordinary flow, unlike a conventionally permeable reservoir.
Hydrocarbon migration: The movement of oil and gas from source rocks into other geological formations. Migration delivers petroleum into reservoir rock after it forms in a source rock.
Seal rock: A low-permeability rock layer that restricts fluid movement across it. A seal helps keep buoyant hydrocarbons from escaping the reservoir.

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