Page 371 - Geology and Geochemistry of Oil and Gas

332 APPENDIX C

Reduced temperature The absolute temperature divided by the absolute
critical temperature: T r ¼ T/T cr .
Reduction Process in which a given substance gains electrons.
Reef An organic buildup made of the remains of sedentary
calcareous organisms, especially corals.
Regression [sed] Retreat of the sea from land areas; also, any change
that converts offshore, deep-water condition to the
near-shore, shallow-water conditions. The landward
migration of sedimentary bodies and corresponding
depositional environments. Cf: Transgression.
Regression [stat] A model of the relationship between the expected
value of a random variable and the values of one or
more possibly related variables.
Relative frequency In a particular class interval, a fraction (as decimal or
percentage) of the total number of occurrences or
events in the sample.
Relative permeability Ratio of the effective permeability at a given
saturation of that fluid to the absolute (single-phase
fluid) permeability at 100% saturation.
Repeatability A precision with which a measured value can be
repeated in an experiment.
Replacement When one mineral replaces the another mineral, e.g.,
dolomitization, silicification.
Representative sample A sample that, well enough, represents the
proportions of the whole population.
Resendimentation Refers to sediments, originally formed and deposited
in one environment and subsequently transported to a
completely different environment.
Reservoir A subsurface accumulation of crude oil or natural gas
under adequate trap conditions.
Reservoir pressure The average pressure within the reservoir at any given
time.
Reservoir rock A porous and permeable rock holding an
accumulation of crude oil and/or natural gas.
Sandstones and carbonates (limestones and
dolomites) are the usually encountered reservoir
rocks.
Resin (a) Any of various hard, brittle, transparent or
translucent substances formed esp. in plant secretion
and obtained as exudates of recent or fossil origin by
the condensation of fluids or the loss of volatile oil.
Resins are yellowish to brown in color, with a
characteristic luster; they are fusible and flammable,
are soluble in ether and other organic solvents but not
in water.