PEC EPE Petro-Gas key terms

The fraction of a rock's bulk volume that is pore space, expressed as a percentage or decimal. It determines how much oil, gas, or water the rock can store.

A measure of how easily a rock transmits fluid through its connected pores under a pressure gradient. It is reported in darcies or millidarcies and controls flow rate.

The fraction of pore volume filled with water in a reservoir rock. Its complement, one minus water saturation, represents the hydrocarbon saturation used in volumetric estimates.

The effective permeability of a particular phase at a given saturation divided by the rock's absolute permeability. It describes how easily oil, gas, and water flow together.

A volumetric accounting method that equates underground fluid withdrawal to expansion of reservoir fluids and rock. It estimates original hydrocarbons in place and identifies the dominant drive mechanism.

The pressure at which the first bubble of dissolved gas comes out of solution from crude oil at reservoir temperature. Below it, gas evolves and oil shrinks.

The density of drilling fluid, usually reported in pounds per gallon or kilograms per cubic metre. It must exceed formation pore pressure while remaining below the fracture gradient.

An unintended influx of formation fluid into the wellbore caused by formation pressure exceeding the hydrostatic pressure of the drilling fluid. If uncontrolled, it can escalate into a blowout.

The bottom end of a casing string, cemented in place to provide a pressure-tight seal. It anchors subsequent drilling and is tested for formation integrity.

A stack of hydraulically operated rams and annular seals installed at the wellhead. It closes the wellbore around drill pipe, tubing, or an open hole to prevent uncontrolled flow.

The rate of change of wellbore inclination and azimuth over a measured course length, commonly expressed in degrees per thirty metres. High values increase torque, drag, and casing wear.

A curve or equation describing how production rate from the reservoir into the wellbore varies with bottomhole flowing pressure. It defines the well's deliverability.

Any method that adds energy to produced fluids when natural reservoir pressure is insufficient to lift them to surface. Common forms are gas lift, electric submersible pumps, and rod pumps.

The fraction of water in the total liquid produced by a well, expressed as a percentage. Rising water cut signals aquifer influx or breakthrough and reduces oil production efficiency.

A dimensionless number representing extra pressure loss or gain near the wellbore caused by damage, perforation, or stimulation. Positive skin indicates damage; negative skin indicates improvement.

A systems-engineering technique that compares the pressure-rate performance of inflow from the reservoir with outflow through tubing, choke, and surface facilities to find the operating point.

The ratio of a gas's molecular weight or density to that of air at the same conditions. It is used to estimate gas properties and is typically around 0.6 to 0.8 for natural gas.

Also called the compressibility factor; it corrects the ideal gas law for real-gas behaviour. It equals the ratio of actual gas volume to ideal volume at the same pressure and temperature.

The pressure, at a given temperature, at which the first liquid hydrocarbon droplets condense from a gas. It sets the minimum operating pressure for gas transmission.

An ice-like solid in which water molecules form cages enclosing small gas molecules under high pressure and low temperature. It can block pipelines, valves, and wellbores.

The formation of liquid from a gas-condensate fluid as reservoir pressure falls below the dew point. The liquid drops out in the reservoir and becomes difficult to produce.

A gas-processing process that removes hydrogen sulphide and carbon dioxide by absorbing them into a chemical amine solution, which is then regenerated by heating.

A gas-processing method that removes water vapour by contacting gas with a hygroscopic glycol, usually triethylene glycol. It lowers the water dew point to prevent hydrates and corrosion.

The practice of driving a device called a pig through a pipeline to clean the bore, inspect the wall, or separate batches of different products.

A set of contractual quality limits that pipeline or sales gas must meet, including heating value, hydrogen sulphide, carbon dioxide, water content, and hydrocarbon dew point.

A fine-grained, organic-rich sedimentary rock that generates oil or gas when buried and heated to sufficient maturity. Its kerogen type and maturation control the hydrocarbons produced.

A geological configuration that prevents hydrocarbons from migrating further, allowing them to accumulate. Common types are anticlines, fault blocks, and stratigraphic pinch-outs sealed by impermeable rock.

A geophysical method that records sound waves reflected from boundaries where acoustic impedance changes. The resulting images reveal subsurface structure, faults, and potentially reservoir properties.

A thermal maturity measurement based on the reflectivity of vitrinite particles under a microscope. Values near 0.6 to 1.0 percent generally correspond to the oil window.

An empirical relationship that estimates water saturation from formation resistivity, porosity, water resistivity, and cementation and saturation exponents. It applies to clean, water-wet sandstones.

A borehole measurement of a formation's resistance to electrical current. Because hydrocarbons do not conduct, high resistivity together with porosity indicates potential hydrocarbon saturation.

The sum of future cash flows discounted to today's value at a chosen rate. A positive NPV indicates that a project is expected to create value above the required return.

The probability-weighted average of all possible outcomes of a decision. It is used in decision trees to compare risky alternatives on a consistent value basis.

A risk-management principle requiring risks to be reduced as low as reasonably practicable, balancing the cost of further controls against the benefit of reduced harm.

A structured team technique that systematically examines deviations from design intent in a process plant, using guide words to identify hazards and operability problems.

A situation in which a professional's personal, financial, or family interest could improperly influence judgement. It must be disclosed and managed to protect integrity and trust.