Investigation of Stress State During Cement Hardening and its Effect on Failure of Cement Sheath in Shale Gas Wells

2021 ◽  
pp. 1-21
Author(s):  
Chaojie Zhao ◽  
Yanxin Jin ◽  
Jun Li ◽  
Musharraf Zaman ◽  
Xue Wang ◽  
...  
Keyword(s):  
Stress State ◽  
Shale Gas ◽  
Hoop Stress ◽  
Cement Slurry ◽  
Gas Wells ◽  
Initial Stress State ◽  
Measurement Capability ◽  
Cement Interface ◽  
Sheath Formation ◽  
Cement Sheath

Abstract Consideration of initial stress state after cement hardening provides a vital basis for the prediction of cement failure, which has been overlooked in previously published methodologies partly due to the difficulties in examining this problem rationally. In the present study, the hoop stress at casing-cement interface during cement hardening is investigated experimentally based on the full-scale casing-cement sheath-formation system (CCFS) facility, which is equipped with the real-time stress-strain measurement capability. The hoop stress at casing-cement interface during cement hardening drops sharply, rather than equating with the initial annulus pressure of cement slurry. It presents a higher drawdown under higher annulus pressure and thinner casing, and a lower drawdown under elastic cement slurry and thicker cement sheath. Furthermore, an analytical model taking the effect of cement hardening into account is developed to predict the integrity of cement sheath. Reliability of the model is verified by comparison with field observations. Excellent agreements are observed. The results illustrate that the tensile cracks are likely to occur at the inner cement (inner surface of cement sheath) by the effect of cement hardening, since the hoop stress at inner cement during cement hardening drops greatly and even becomes tensile. A detailed sensitivity analysis illustrates that an elastic cement slurry with a lower elastic modulus works more effectively, which can resolve the SCP problem in shale gas wells.

scholarly journals Integrity tests of cement sheath for shale gas wells under strong alternating thermal loads

2020 ◽  
Vol 7 (6) ◽  
pp. 671-679
Author(s):  
Yuanhua Lin ◽  
Kuanhai Deng ◽  
Hao Yi ◽  
Dezhi Zeng ◽  
Liang Tang ◽  
...  
Keyword(s):  
Shale Gas ◽  
Thermal Loads ◽  
Gas Wells ◽  
Cement Sheath ◽  
Integrity Tests

Study on Preapplied Annulus Backpressure Increasing the Sealing Ability of Cement Sheath in Shale Gas Wells

SPE Journal ◽  
2021 ◽  
pp. 1-17
Author(s):  
Kui Liu ◽  
Shidong Ding ◽  
Shiming Zhou ◽  
Qian Tao ◽  
Linhai Zhang ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Analytical Model ◽  
Shale Gas ◽  
Radial Stress ◽  
Fluid Pressure ◽  
Outer Diameter ◽  
Gas Wells ◽  
Sealing Ability ◽  
Cement Sheath ◽  
Sealing Failure

Summary Annulus pressure buildup (APB) problems in shale gas wells seriously affected on the safety and efficient exploitation of shale gas all around the world. The sealing failure of the cement sheath on interfaces caused by periodically changed fluid pressure in casing during hydraulic fracturing is treated as the main reason for APB in shale gas wells. Many methods are put forward to solve the APB problem in the field, and fortunately, the preapplied annulus backpressure (PABP) method shows an excellent utility. In this paper, an analytical model is established to explain the mechanism of the PABP method increasing the sealing ability of the cement sheath. The residual strain of the cement sheath and radial stress on interfaces are considered to analyze the factors that affect the effectiveness of the PABP method. In addition, based on the field data, an experimental device is established to test the validity of the PABP method and to certify the accuracy of the analytical model established in this paper. The analytical results show that the thickness of the casing has little effect on radial stress on interfaces. The outer diameter of the casing and the thickness of the cement sheath can temperately affect the radial stress. The elastic modulus of the cement sheath and the formation rock can significantly affect the radial stress. The higher elastic modulus of the cement sheath can dramatically increase the radial stress on interfaces. On the contrary, the higher elastic modulus of formation rock will induce smaller radial stress on the interfaces. In the field, the number of newly added shale gas wells with APB problems has dramatically decreased by using the PABP method. The work in this paper can be significantly useful for researchers and engineers to reduce the APB in shale gas wells.

The maximum permissible fracturing pressure in shale gas wells for wellbore cement sheath integrity

2018 ◽  
Vol 56 ◽  
pp. 324-332 ◽  
Author(s):  
Boyun Guo ◽  
Liqun Shan ◽  
Shuxian Jiang ◽  
Gao Li ◽  
Jim Lee
Keyword(s):  
Shale Gas ◽  
Gas Wells ◽  
Cement Sheath

Analytical Method to Evaluate Casing Stress during Multi-Fracturing for Shale Gas Wells

2019 ◽  
Vol 944 ◽  
pp. 1050-1060 ◽  
Author(s):  
Xue Li Guo ◽  
Jun Li ◽  
Yi Jin Zeng ◽  
Shi Dong Ding ◽  
Xu Zhang
Keyword(s):  
Analytical Model ◽  
Shale Gas ◽  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Sensitivity Analyses ◽  
Stress Deviator ◽  
Fluid Temperature ◽  
Analysis Model ◽  
Gas Wells ◽  
Cement Sheath

An analysis model of casing stress distribution and its variation regularities presents several challenges during hydraulic fracturing of shale gas wells. In this paper, an analytical mechanical - thermal coupling method was provided to evaluate casing stress. In the model, the casing, cement sheath, and formation (CCF) system was divided into four stress field induced by uniform stress, deviator stress, shear stress, and thermal stress,. Based on this analytical model, the parametric sensitivity analyses of casing stress such as mechanical properties, operation parameters, and geo-stress were conducted during multi-fracturing. The results indicated the casing stress increased first, then decreased with the increase of cement sheath modulus. However, it always decreased with the increase of cement sheath Poisson's ratio and the injection fluid temperature. The casing stress increased dramatically with the increase of δ. However, it decreased first, then increased with the increase of fracturing pressure. Higher fluid temperature, cement with small modulus and large Poisson’s ratio were effective to decrease the casing stress. In conclusion, the analytical model can accurately predict casing stress and become an alternative method of casing integrity evaluation for shale gas wells. It is a useful and efficient method for a preliminary design, being capable of simulation the actual situations in order to assess the casing stresses and integrity.

scholarly journals New Analytical Method to Evaluate Casing Integrity during Hydraulic Fracturing of Shale Gas Wells

2019 ◽  
Vol 2019 ◽  
pp. 1-19 ◽  
Author(s):  
Jun Li ◽  
Xueli Guo ◽  
Gonghui Liu ◽  
Shuoqiong Liu ◽  
Yan Xi
Keyword(s):  
Stress Field ◽  
Hydraulic Fracturing ◽  
Shale Gas ◽  
Poisson’S Ratio ◽  
New Method ◽  
Poisson's Ratio ◽  
Sensitivity Analyses ◽  
Fluid Temperature ◽  
Gas Wells ◽  
Cement Sheath

An accurate analysis of casing stress distribution and its variation regularities present several challenges during hydraulic fracturing of shale gas wells. In this paper, a new analytical mechanical-thermal coupling method was provided to evaluate casing stress. For this new method, the casing, cement sheath, and formation (CCF) system was divided into three parts such as initial stress field, wellbore disturbance field, and thermal stress field to simulate the processes of drilling, casing, cementing, and fracturing. The analytical results reached a good agreement with a numerical approach and were in-line with the actual boundary condition of shale gas wells. Based on this new model, the parametric sensitivity analyses of casing stress such as mechanical and geometry properties, operation parameters, and geostress were conducted during multifracturing. Conclusions were drawn from the comparison between new and existing models. The results indicated that the existing model underestimated casing stress under the conditions of the geostress heterogeneity index at the range of 0.5–2.25, the fracturing pressure larger than 25 MPa, and a formation with large elastic modulus or small Poisson’s ratio. The casing stress increased dramatically with the increase of in situ stress nonuniformity degree. The stress decreased first and then increased with the increase of fracturing pressure. Thicker casing, higher fluid temperature, and cement sheath with small modulus, large Poisson’s ratio, and thinner wall were effective to decrease the casing stress. This new method was able to accurately predict casing stress, which can become an alternative approach of casing integrity evaluation for shale gas wells.

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