PSI - Issue 58

Heng Yang et al. / Procedia Structural Integrity 58 (2024) 144–149 H. Yang et al. / Structural Integrity Procedia 00 (2022) 000–000

147

4

cement sheath has shear failure; In Fig. 3 (b), the circumferential stress is the compressive stress, and the cement sheath will not have tensile failure. It can be seen from Fig. 4 that the contact pressures of cement sheath interfaces increase with the increase of creep time. And the larger the uniform horizontal in-situ stress is, the larger the contact pressures of cement sheath interfaces are. In Fig. 4, contact pressure>0, the cement sheath will not have debonding failure.

σ H =σ h =50MPa

σ H =σ h =60MPa

σ H =σ h =70MPa

σ H =σ h =80MPa

σ H =σ h =90MPa

σ H =σ h =50MPa

σ H =σ h =60MPa

σ H =σ h =70MPa

0.0035

-5

σ H =σ h =80MPa

σ H =σ h =90MPa

0.0030

-10

0.0025

-15

0.0020

-20

0.0015

-25

PEEQ

0.0010

-30

0.0005

-35 Circumferential Stress(MPa)

0.0000

-40

-100 0 100 200 300 400 500 600 700 800 -0.0005

0

100 200 300 400 500 600 700 800

Time(h)

Time(h)

Fig. 3. Variation of PEEQ and circumferential stress of the cement sheath with the time of formation creep under uniform horizontal in-situ stress: (a) PEEQ; (b) circumferential stress.

σ H =σ h =50MPa

σ H =σ h =60MPa

σ H =σ h =70MPa

σ H =σ h =50MPa

σ H =σ h =60MPa

σ H =σ h =70MPa

σ H =σ h =80MPa

σ H =σ h =90MPa

100

σ H =σ h =80MPa

σ H =σ h =90MPa

90

90

80

80

70

70

60

60

50 Contact Pressure (MPa)

50 Contact Pressure (MPa)

40

40

0

100 200 300 400 500 600 700 800

0

100 200 300 400 500 600 700 800

Time (h)

Time (h)

Fig. 4. Variation of the contact pressures of cement sheath interfaces with the time of formation creep under uniform horizontal in-situ stress: (a) casing-cement sheath interface; (b) cement sheath-formation interface.

3.2. Measures to reduce the risk of failure of the cement sheath integrity The simulation conditions are: σ � �σ � � 50MPa, other parameters of the model remain unchanged. After 30 days of formation creep, the PEEQ of the cement sheath changes with the Elastic modulus of the cement sheath and Poisson's ratio of the cement sheath as shown in Fig. 5 (a) and Fig. 5 (b) respectively. It can be seen from Fig. 5 that reducing the Elastic modulus of the cement sheath and increasing the Poisson's ratio of the cement sheath can reduce the PEEQ of the cement sheath. That is, it can reduce the risk of shear failure of cement sheath.