Page 370 - Geology and Geochemistry of Oil and Gas

GLOSSARY 331
Q

Quantile [stat] The argument of the cumulative distribution function
corresponding to a specified probability; (of a
sample) the value below which occur a specified
proportion of the observations in the ordered set
of observations.
Quartile [stat] The argument of the cumulative distribution function
corresponding to a probability of either 1 (first or
4
lower quartile), 1 (second or middle quartile or
2
3
median) or (third or upper quartile). In a sample, the
4
value below which a quarter, one-half or three-
quarters of the observations occurs in the ordered set
of observations.
R
Radial flow Two-dimensional flow from all points around a 3601
circle within a formation to a centered well.
Radioactivity logging The recording of the natural or induced radioactive
characteristics of subsurface formations. A
radioactivity log normally consists of two recorded
curves: a gamma-ray curve and a neutron curve.
Ramp A carbonate depositional surface that dips very gently
(o11) in a seaward direction, passing imperceptibly
from shallow to deep water.
Rate of Penetration (ROP) Speed with which the drilling bit cuts through the
formation.
Rate of shear Rate (in rpm) at which an action resulting from
applied forces causes or tends to cause two adjacent
parts of a body to slide relative to each other in a
direction parallel to their plane of contact.
Recovery The petroleum produced from the reservoir in % (or
fraction) of the total oil in-place reserves; it is
subdivided into primary, secondary, and tertiary
recovery.
Recrystallization Term that refers to an increase in the size of existing
crystals without a change in mineralogy.
Redox potential (Eh) A scale of values, measured as electric potential in
volts, indicating the ability of a substance or solution
to cause reduction or oxidation reactions under non-
standard conditions. The higher the value of Eh, the
more oxidizing the conditions.
Reduced pressure The absolute pressure at which the gas exists divided
by the absolute critical pressure: p r ¼ p/p cr .