In
rock physics and
petrophysics
Petrophysics (from the Greek πέτρα, ''petra'', "rock" and φύσις, ''physis'', "nature") is the study of physical and chemical rock properties and their interactions with fluids.
A major application of petrophysics is in studying reservo ...
, the mudrock line, also called Castagna's equation or Castagna's relation, is an
empirical
Empirical evidence for a proposition is evidence, i.e. what supports or counters this proposition, that is constituted by or accessible to sense experience or experimental procedure. Empirical evidence is of central importance to the sciences and ...
linear relation between
seismic P-wave
A P wave (primary wave or pressure wave) is one of the two main types of elastic body waves, called seismic waves in seismology. P waves travel faster than other seismic waves and hence are the first signal from an earthquake to arrive at any ...
velocity and
S-wave velocity in
brine
Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for br ...
-saturated siliciclastic rocks (i.e.
sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates) ...
s and
shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
s).
The equation reads:
:
Where
and
refer to P-wave velocity and S-wave velocity, respectively. Velocities are given in kilometers per second (km/s).
The name of the equation refers to
John Castagna
John Castagna is an American geophysicist, known for the Mudrock line, currently the Margaret S. and Robert E. Sheriff Endowed Faculty Chair in Applied Seismology at Universidad Politécnica del Centro and formerly the Edward L. McCullough Chair.
...
, professor of
exploration geophysics at the
University of Houston
The University of Houston (UH) is a Public university, public research university in Houston, Texas. Founded in 1927, UH is a member of the University of Houston System and the List of universities in Texas by enrollment, university in Texas ...
,
[http://www.geosc.uh.edu/people/faculty/john-castagna/index.php "University of Houston directory"] who discovered the relation while working for
ARCO
ARCO ( ) is a brand of gasoline stations currently owned by Marathon Petroleum after BP sold its rights. BP commercializes the brand in Northern California, Oregon and Washington, while Marathon has rights for the rest of the United States an ...
, an oil company that is now a subsidiary of
Marathon Petroleum
Marathon Petroleum Corporation is an American petroleum refining, marketing, and transportation company headquartered in Findlay, Ohio. The company was a wholly owned subsidiary of Marathon Oil until a corporate spin-off in 2011.
Following it ...
.
References
Geophysics
Well logging
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