Acoustic travel time test

Test may be carried out both on saturated and unsaturated cylindrical specimen. The travel time of acoustic signal through the sample and two steel platens is represented on figures 20, 21. The test setup is such that the oscilloscope triggers when the pulse is fired [1]. Then the receiver captures and records the travel time of this signal. Calibration time for travel through the steel platens exists and it is taken in account in calculation travel time for S and P waves (figure 20). At the figure 19 it is shown the procedure of this test.

Figure 19. Procedure of the determination travel time for P and S acoustic waves.

Figure 20. Signal of P wave

Figure 21. Signal of S wave

After determination the travel time of each type of waves it is possible to define velocities of P and S waves by means of next equations:

	(8)
	(9)

where L – length of the sample;

– travel time of S and P waves respectively.

After that it can possible to determine the modulus of elasticity (Young’s modulus), E and Poisson’s coefficient, 𝜈:

(10)

(11)

The results of calculation are represented in the table 5.

𝜌, kg/	Length, m	, µsec	, µsec	, m/sec	, m/sec	ν	E, GPa
2300	0.076	26.08	17.14	2914.11	4434.072	0.12	43,745

Table 5. Results of the Acoustic travel time test

The results that are derived from elastic components test and the results that are derived from this test are different because of different physics of the measurements. Also difference between two samples in these tests may influence on end results. So at the elastic components test the load is applied on the sample and specimen deforms. But in the acoustic travel time test the sample does not deform (table 6).

Type of test	ν	E, GPa
Elastic components test	0.163	25.377
Acoustic travel time test	0.12	43,745

Table 6. Modulus of elasticity (Young’s modulus), E and Poisson’s coefficient, 𝜈 from different tests

Conclusion

Results of this work are determinated values of next parameters:

• Poisson’s coefficient

• Young’s modulus

• cohesion and internal fraction angle

• triaxial factor

• tensile strength

• uniaxial compressive strength

It should be noted that elastic coefficient were be obtained with two different method and we can say that different methods can have strong influence on results. That is why laboratory engineer must very careful calculate and compare all parameters.

Mechanical properties of the rock that are obtained from these and other tests can strongly help with development oil field as in reservoir evaluation as in reservoir engineering.