bubble-point pressure: the pressure at which gas, held in solution in crude oil, breaks out of solution as free gas. Syn: saturation pressure.

density-driven convection: convection (circular motion) that occurs owing to differences in density of fluids.

diagenesis: all the chemical, physical, and biologic changes undergone by a sediment after its initial deposition, and during and after its lithification, exclusive of surficial alteration (weathering) and metamorphism.

diffusion: the process by which both ionic and molecular species dissolved in water move from areas of higher concentration to areas of lower concentration (Fetter, 1994). Movement is random and is proportional to the gradient of concentration. The process tends to distribute the particles more uniformly.

fluid-density segregation: segregation of two different fluids (water and oil, gas and water, etc.) owing to differences in their density.

fluid-flow communication: two wells communicate with each other in a fluid-flow sense if a change in rock pore pressure at one well can be detected in the second well.

four-dimensional seismic: a time-lapse seismic survey of three-dimensional data, the fourth dimension being lapsed time. Abbr.: 4-D.

gas-cap expansion (drive): the force exerted by the energy released from expanding gas of a gas cap, used to produce (drive) oil from the reservoir.

gas:oil ratio (GOR): a measure of the volume of gas produced with oil, expressed in cubic feet per barrel or cubic meters per metric ton.

genetic units: sedimentary bodies representing complex genetically related facies formed in the same environment, and mostly as the effect of a single leading process, e.g., alluvial deposits, deltaic deposits, lagoonal deposits, or marine deposits.

HKW: abbr.: highest known water, the highest subsea depth at which water occurs; usually measured for individual well bores.

hydrodynamics: the aspect of hydromechanics that deals with forces that produce motion.

LKG: abbr.: lowest known gas, the lowest subsea depth at which gas occurs; usually measured for individual well bores.

LKO: abbr.: lowest known oil, the lowest subsea depth at which oil occurs; usually measured for individual well bores.

normally pressured system: a normally pressured system is a system where the pressure at the hydrocarbon-water contact is determined by the hydrostatic head.

production-time-series analysis: consists of graphing and mapping of oil, gas, water cut, fluid levels, and pressure-depletion variation over the producing life of a reservoir. Next, fluid-flow trends within the reservoir are established from a set of production-performance maps that illustrate initial potential, cumulative and current production, gas:oil ratio (GOR), fluid levels, water cut, and pressure depletion on a per-well basis. Anomalies in these maps can indicate barriers to fluid flow, which may also indicate reservoir compartmentalization.

solution-gas drive: in a solution-gas-drive reservoir (known also as dissolved-gas-drive), the lighter hydrocarbon components that are dissolved in the oil before it is produced come out in the form of gas as the reservoir pressure is depleted. The solution gas coming out of the oil expands to force the oil into the well bore.

stiff diagram: a graphical representation of cation and anion concentration within a water sample. The concentration of cations Na+k, Ca, and Mg and the anions Cl, HCO3, and SO4, are plotted together on a diagram with lines connecting them in to a polygon. The shape of the polygons for different samples can easily be compared to look for similarities and differences in water chemistry.

water (aquifer) drive: Any process by which energy for the production of oil is derived principally from the pressure of water in the formation. A water-drive reservoir is one from which the oil or gas is wholly or partly expelled by pressure owing to encroaching water. The water may have been in the reservoir initially, in which case the drive is natural, or it may have been introduced artificially.

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