FIG. 3 ELASTIC WAVE VELOCITY, Φ RELATIONSHIP
V,
k
m/
s
ec
4. 5
4.0
3. 5
3.0
2. 5
2.0
1. 5
1.0
0.5
Φ,
0 2 4 6 8 10 12 14 16
Vp
Vs
Saturated Vp ratio Dry Vp
Saturated Vs ratio Dry Vs
igneous rock samples collected from
a Carboniferous formation at a depth
of 3,600 m in the Junggar basin (Table
1, Fig. 1). X-ray diffraction and thin-section authentication determined the
rocks’ mineral compositions. Technicians processed the samples into 50-
mm long cylinders with a diameter of
25 mm and baked them at 50° C. for
48 hr. The dried samples were maintained in a vacuum state.
Researchers induced water-satura-tion by submerging the rock samples
under atmospheric conditions for 48
hr. Plastic film wrapped on the side
surface of the samples prevented moisture loss. 24 25
The GCTS-RTR-1000 rock mechanics system tested each sample.
Technicians replaced the system’s
standard hydraulic pressure head with
a bearing-type acoustic wave transducer to apply axial pressure to samples with a maximum loading capacity
of up to 960 khz. The transversal-wave
excitation center frequency measured
620 khz with an accuracy of 0.1 µs.
The experiments used longitudinal
and transversal waves with a RIGOL-
DS5022M oscilloscope connected to a
computer for synchronous acquisition
of time differences (Fig. 2). Length-measurement error and data acquisition time resolution were 0.1 mm and
0.02 µs, respectively.
The transducer converted the pulse
transmitter’s high-voltage signal into
ultrasonic waves, which were then applied to each rock sample. The oscilloscope measured the difference (T) between ultrasonic pulse generation and
reception times. The ultrasonic waves’
transmission times (Tt) in the rock
samples were calculated by deducting the transmission time
(T0) in the coupling layer. The wave velocity (V) is calculated
by dividing Tt by rock sample length (L), (V = (T-T0)/L).
Analysis
Under an axial pressure of 5 MPa and at normal tempera-
ture, Vp in the water-saturated rock core was higher than
that in the dry rock sample. The average Vp ratio before and
after water saturation was 1. 17. The Vp ratio for basalt was
1. 32, which is higher than average. Andesite’s was closer to
the average. Diorite porphyrite and granite porphyry both
wave velocities in igneous cores with the ultrasonic pulse
method and analyzed the rocks’ influencing internal factors,
revealing the physical mechanisms affecting elastic wave
velocity. In addition, lab work applied well testing data to
calibrate existing logs. Fluid-type identification in igneous
rock reservoirs was guided by existing research on identify-
ing gas and water zones using Vp and Vs.
Method, apparatus
The experiment analyzed 15 intermediate-basic and acid
