Well Logging (???)

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Well Logging(???)

• ?????????
• ?????
• 2008. 12. 08-15

2
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• ??(well logging)????????????,??????????????,??????
  ???,?????????????????????????????????
• ????????????,??????????????????

3
N
M
A
?????????(A)??????(M?N)??????,??????????????
?????????????????????????????????????????
4
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5
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• Schlumberger ???1912????????????????????????,?1927
  ????Pechelbronn ??????????????????????,???????(???
  ???),???????????????????????????????,??,??????????
  ??????
• 1931????????????,????????????????,1943??????????,?
  ?????????

6
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• 1947???????????,?????????????????????????????,1950
  ??,??????????,????????????????
• 1951??????????????????????,??????????????

7
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• 1951???????????????????,?????????????,????????????
  ????????,?1957???????????????,??1962??????????????
  ??
• ???????,???1951?????????,??1960??????????,???1965?
  ??????????

8
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• ??????1966?????,???????????????,??1978??,?????????
  ???????????????????????
• ??,?1988?,?????????(Measurement-While-Drilling,
  MWD)???,?????????????????,???????????,???????????

9
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• ???????????????,?????????,
• ?????????(????????????)?
• ????????????(?????),
• ????????(???????)???????????(?????)?
• ?????????????,?????????????????

10
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11
????

• ????????????????????????
• ????
• ???????(SP Log)
• ????(GR Log)
• ????(Caliper Log)
• ?????
• ????
• ??????
• ????
• ????
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12
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15
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• ???????????????SP ???,?SP ???
• ????????,????????????,??????????,???????
• ?????,?????????,?????????????????????,????????????
  ?,??,???????????????,??????????????,SP
  ????????(??????)???

16
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• ??????????????????????????????????,???????????,???
  ?,??????????
• ??????????????????(Rw) ?

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SP Log

• The SP log is recorded on the left hand track of
  the log and is used to
• (1) detect permeable beds
• (2) detect boundaries of permeable beds
• (3) determine formation water resistivity (Rw),
  and
• (4) determine the volume of shale in permeable
  beds (Vsh)

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SP Log

• The concept of static spontaneous potential (SSP)
  is important because SSP represents the maximum
  SP that a thick, shale-free, porous and permeable
  formation can have for a given ratio between
  Rmf/Rw.
• The SP value that is measured in the borehole is
  influenced by bed thickness, bed resistivity,
  invasion, borehole diameter, shale content, and
  most important the ratio of Rmf/Rw.

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SP Log

• Bed thickness
• As a formation thins (i.e. lt 10ft thick) the SP
  measured in the borehole will record an SP value
  less than SSP.
• Bed resistivity
• Higher resistivities reduce the deflection of the
  SP curves.
• Borehole and invasion
• Hilchie (1978) indicates that the effects of
  borehole diameter and invasion on the SP log are
  very small and, in general, can be ignored.
• Shale content
• The presence of shale in a permeable formation
  reduces the SP deflection.

20
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• ?????????????????,???????????,????????????????????
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• ??,??????????????????,(??K40)??,??????????????????
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  ????????(???)?

21
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Gamma Ray Logs

• Gamma ray logs measure natural radioactivity in
  formations and because of this measurement, they
  can be used for identifying lithologies and for
  correlating zones. Shale- free sandstones and
  carbonates have low concentrations of radioactive
  material, and give low gamma ray readings.
• As shale content increases, and gamma ray log
  response increases because of the concentration
  of radioactive material in shale. However, clean
  sandstone (i.e. low shale content) may also
  produce a high gamma ray response if the
  sandstone contains potassium feldspars (????),
  micas (??), glauconite (???????), or uranium
  -rich water (?????).

23
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25
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• ???????????????????(???)??????????????????????????
  ,??????????(???????)?

where
sonic derived porosity
interval transit time of the matrix
interval transit time of formation
interval transit time of the fluid in the well
bore (fresh mud189 salt mud185)
compaction factor The compaction factor is
obtained from the following formula
26
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27
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• ??????????????????????(????????????)??,???????????
  ?????
• ????????????(???????)???????(?????????2.65g/cm3)??
  ?????(????????????1.1g/cm3),??????????(???????)?

where fden density derived porosity ?ma
matrix density ?b formation bulk density ?f
fluid density (1.1 salt mud, 1.0 fresh mud, and
0.7 gas)
28
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29
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where
neutron-density porosity
neutron porosity (limestone unit)
density porosity (limestone unit)
neutron-density porosity
where
neutron porosity (limestone unit)
density porosity (limestone unit)
31
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32
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33
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Borehole Environment
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Borehole Environment (cont.)

• Hole Diameter (dh)
• A wells borehole size is described by the
  outside diameter of the drill bit. The size of
  the borehole is measured by a caliper log(????).
• Drilling Mud (Rm)
• Today, most wells are drilled with rotary bits
  and use special mud as a circulating fluid.
• Mudcake (Rmc)
• As invasion occurs, many of the solid particles
  (i.e. clay minerals from the drilling mud) are
  trapped on the side of the borehole.

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Borehole Environment (cont.)

• Mud Filtrate (Rmf)
• Fluid that filters into the formation during
  invasion.
• Invaded Zone(???)
• The zone which is invaded by mud filtrate is
  called the invaded zone. It consists of a flushed
  zone (Rxo) and a transition or annulus (Ri) zone.
  
• Flushed zone (Rxo)
• Occurs close to the borehole where the mud
  filtrate has almost completely flushed out a
  formations hydrocarbons and/or water (Rw).

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Borehole Environment (cont.)

• The transition or annulus zone (Ri)
• A formations fluids and mud filtrate are mixed,
  occurs between the flushed (Rxo) zone and the
  uninvaded zone (Rt).
• Flushed Zone (Rxo)
• The flushed zone extends only a few inches from
  the well bore and is part of the invaded zone.
• Uninvaded Zone (Rt)
• The uninvaded zone is located beyond the invaded
  zone. Pores in the uninvaded zone are
  uncontaminated by mud filtrate instead, they are
  saturated with formation water (Rw), oil, or gas.

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Borehole Environment (cont.)

• Diameter of invasion (di and dj)
• The depth of mud filtrate invasion into the
  invaded zone is referred.
• Water saturation of uninvaded zone (Sw)
• Water saturation of flushed zone (Sxo)

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Invasion and Resistivity Profiles

• Invasion and resistivity profiles are
  diagrammatic, theoretical, cross sectional views
  moving away from the borehole and into a
  formation.
• They illustrate the horizontal distributions of
  the invaded and uninvaded zones and their
  corresponding relative resistivities.
• There are three commonly recognized invasion
  profiles (1) step, (2) transition, and (3)
  annulus.

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Step Profile

• The step profile has a cylindrical geometry with
  an invasion diameter equal to dj.
• Shallow reading, resistivity logging tools read
  the resistivity of the invaded zone (Ri), while
  deeper reading, resistivity logging tools read
  true resistivity of the uninvaded zone (Rt).

Ro resistivity of the zone with pores 100
filled with formation water (Rw). Also called wet
resistivity
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Transition profile

• The transient profile also has a cylindrical
  geometry with two invasion diameters di (flushed
  zone) and dj (transition zone).
• It is probably a more realistic model for true
  borehole conditions than the step profile.
• Three resistivity devices measure resistivities
  of the flushed, transition, and uninvaded zones
  Rxo, Ri, and Rt.

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Annulus profile

• An annulus profile is only sometimes recorded on
  a log because it rapidly dissipates in a well.
• However, it is very important to a geologist
  because the profile can only occur in zones which
  bear hydrocarbons.
• As the mud filtrate invades the
  hydrocarbon-bearing zone, hydrocarbons move out
  first. Next, formation water is pushed out in
  front of the mud filtrate forming an annulus
  (circular) ring at the edge of the invaded zone.

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44
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45
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Resistivity

• Resistivity is the rock property on which the
  entire science of logging first developed.
• Resistivity is the measurement of resistance the
  reciprocal of resistivity is conductivity.

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Temperature of Formation

• Formation temperature (Tf) is also important in
  log analysis because the resistivities of the
  drilling mud (Rm), the mud filtrate (Rmf), and
  the formation water (Rw) vary with temperature.
• The temperature of a formation is determined by
  knowing
• (1) formation depth
• (2) bottom hole temperature (BHT)
• (3) total depth of the well (TD)
• (4) surface temperature.

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Temperature of Formation (cont.)

• The formation temperature is also calculated
  (Asquith, 1980) by using the linear regression
  equation

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Temperature Gradient Calculation

• Assume
• y bottom hole temperature (BHT) 250 F
• x total depth (TD) 15,000 ft
• c surface temperature 70 F
• Solve for m (i.e. slope or temperature
  gradient)

70 ?
TD 15000 ft
250 ?
50
Temperature Gradient Calculation (solution)
51
Formation Temperature Calculation

• Assume
• m temperature gradient 0.012 F /ft
• x formation depth 8,000ft
• c surface temperature 70 F
• Calculate the formation temperature at 8,000
  ft

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Formation Temperature Calculation (solution)
53
Resistivity Calculation

• After s formations temperature is determined
  either by chart or by calculation, the
  resistivities of the different fluids (Rm, Rmf,
  or Rw) can be corrected to formation temperature.
• Figure 9 is a chart that is used for correcting
  fluid resistivities to formation temperature.
  This chart is closely approximated by the Arps
  formula

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Fig. 8
55
Fig. 9
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Resistivity Calculation

• Using a formation temperature of 166 F and
  assuming an Rw of 0.04 measured at 70 F, the Rw
  at 166 F will be
• Resistivity values of the drilling mud (Rm), mud
  filtrate (Rmf), mudcake (Rmc), and the
  temperatures at which they are measured, are
  recorded on a logs header.

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Resistivity Calculation (solution)
58
Log Header (??)
Note sometimes, as in this example, a value for
the Rmc is not recorded on the header.
59
Exercise 1

• Given
• Surface temperature 80 F
• Bottom hole temperature (BHT) 180 F
• Total depth (TD) 10,000 ft
• Formation depth 6,000 ft
• Calculate the formation temperature at 6000 ft

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Exercise 1 (solution)
61
Exercise 2

• Given
• Resistivity of drilling mud (Rm) equals 1.2 at 75
  F
• Formation temperature (Tf) 160 F
• Calculate the resistivity at formation
  temperature (160 F)

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Exercise 2 (solution)
63
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66
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