PSI - Issue 6

Chebyshev Igor et al. / Procedia Structural Integrity 6 (2017) 252–258 Chebyshev I.S./ Structural Integrity Procedia 00 (2017) 000–000

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Fig. 5. a. P-, b. S – wave velocities predicted with linear regression

6. Static elastic modulus

Cylindrical-shape samples with 30 mm in diameter and 60 mm in height are exposed to UCS (unconfined compression strength) and TXC tests (triaxial compression strength) before their deconstruction. Then all the graphs received should have been interpreted based on sample shape and behavior while compression. As a rule, zone of elastic deformation is divided with zone of plastic deformations by point of inflection. It is important to have understanding mechanical and acoustic properties in weak sandstone to develop the stability of wellbore and sand production, because the sand production in plastic zone is more active than in elastic zone, when the skeleton volume changes irretrievable. But this note doesn’t work with weak cemented rocks (Fig.6.). The graph shows (Fig.6.) that Young’s static modulus can be defined in the range of 0.57 – 2.7GPa. Because of their weakly consolidated structure the samples had been frozen and being unfrozen right before testing (Sa, 1997). In this case the calculation of correct static elastic moduli with poroelastic horizontal strain model (Eq. 3, 4) can be difficult.

υ E 1 − υ 2 υ E 1 − υ 2

E 1 − υ 2 E 1 − υ 2

υ 1 − υ

υ 1 − υ υ 1 − υ

υ 1 − υ υ 1 − υ

α P p + α P p +

α T Δ T

(3)

σ H max =

σ V −

ε H +

ε H +

υ 1 − υ

(4)

α P p + α P p +

α T Δ T

σ h min =

σ V −

ε h +

ε h +

Fig. 6. Unconfined compressive strength of weak consolidated sandstone.