Презентация на тему Basic well logging analysis – sonic log

that measures interval transit time (Δt) of a compressional

sound wave traveling through one foot of formation.

Interval transit time (Δt) in microseconds per foot is the reciprocal of the velocity of a compressional sound wave in feet per second.

one or more sound transmitters, and two or more

receivers.

Modern sonic logs are borehole compensated devices (BHC). These devices greatly reduce the spurious effects (假性效應) of borehole size variations (Kobesh and Blizard, 1959), as well as errors due to tilt (傾斜) of the sonic tool (Schlumberger, 1972).

in tracks #2 and #3 (in your example Figure).

A sonic derived porosity curve is sometimes recorded in tracks #2 and #3, along with the Δt curve.

Track #1 normally contains a caliper log and a gamma ray log or an SP log.

dependent upon both lithology and porosity.

Therefore, a formation's

matrix velocity (Table 1) must be known to derive sonic porosity either by chart (Fig. 27) or by formula (Wyllie et al, 1958).

Δtma   
Vma Δtma (μsec/ft)
(ft/sec) (μsec/ft) commonly used
Sandstone 18,000 to 19,500 55.5 to 51.0 55.5 to 51.0
Limestone 21,000 to 23,000 47.6 to 43.5 47.6
Dolomite 23,000 to 26,000 43.5 to 38.5 43.5
Anhydrite 20,000 50.0 50.0
Salt 15,000 66.7 67.0
Casing
(Iron) 17,500 57.0 57.0

formation's matrix velocity must be known
Derive sonic porosity by

chart

9310 ft
Lithology [=] Dolomite (Vma=26000 ft/sec)
Sonic porosity =

?

(2)
Depth = 9320 ft
Lithology [=] Limestone (Vma=21000 ft/sec)
Sonic porosity = ?

= sonic derived porosity
Δtma = interval transit time

of the matrix
Δtlog = interval transit time of formation
Δtf = interval transit time of the fluid in the well bore
(fresh mud = 189；salt mud = 185)

9310 ft
Lithology [=] Dolomite
Mud [=] fresh mud
Sonic porosity

= ?

(2)
Depth = 9320 ft
Lithology [=] Limestone
Mud [=] fresh mud
Sonic porosity = ?

al. (1958) formula for calculating sonic porosity can be

used to determine porosity in consolidated sandstones and carbonates.

Where a sonic log is used to determine porosity in unconsolidated sands, an empirical compaction factor or Cp should be added to the Wyllie et al. (1958) equation:



Where Cp = compaction factor

compaction factor is obtained from:



Where Cp = compaction factor

Δtsh = interval transit time for adjacent shale
C = a constant which is normally 1.0 (Hilchie,1978)

(Δt) of a formation is increased due to the

presence of hydrocarbons (i.e. hydrocarbon effect).

If the effect of hydrocarbons is not corrected, the sonic derived porosity will be too high.

Hilchie (1978) suggests the following empirical corrections for hydrocarbon effect：
Ф = Фsonic × 0.7 (gas)
Ф = Фsonic × 0.9 (oil)

shale (Vsh) is determined, it can be used to

correct the porosity log for shale effect. The formula for correcting the sonic log for volume of shale is (Dresser Atlas, 1979):



Where Δtsh = interval transit time for adjacent shale