Coupling Effect of Transient Temperature-Pressure on Casing String During Volume Fracturing in Shale Gas Wells
Casing deformation has been found to be a very significant issue in the development process of shale gas in China, while the coupling effect of transient temperature-pressure has a significant impact on casing stress, and worthy of study. This paper presented a new numerical investigation to understand the coupling effect of transient temperature-pressure on casing string during volume fracturing. A wellbore temperature model was established to obtain the required input parameters of dynamic temperature boundary. The numerical model considers the coupling effect of transient temperature-pressure and the various cement sheath shapes. The results showed that the temperature of casing changed drastically during fracturing. Under the influence of the coupling effect of transient temperature-pressure, (a) when the cement sheath shape was integrity, the casing stress increased greatly and showed dynamic changes: first increased and then decreased, (b) when there was deficiency in cement sheath, with the increase of the eccentric distance or deficiency angle, the casing stress increased aggravating risk of casing deformation. Rotating the casing string during the cementing process to avoid the deficiency in cement sheath or using warm fracturing fluids to minimize the influence of the coupling effect of transient temperature-pressure are possible innovative strategies to solve these difficult problems.
KeywordsVolume fracturing Shale gas Wellbore temperature field model Coupled thermal-mechanical effect Semi-analytical method
The authors thank the National Natural Science Foundation “Study on optimization of un-uniform clustering perforation for long horizontal inhomogeneous shale formation” (Item No. 51674272), National Science and Technology Major Project “Optimizing technology of cluster perforation completion design in complicated structure wells” (Item No. 2017ZX05009), the Science Foundation of China University of Petroleum (Beijing) “Research on optimization method of cluster perforation parameters in anisotropy shale gas reservoirs” (Item No. 2462015QZDX05), and the State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development “Research on casing loading spectrum under multi-factor coupling effect in shale gas wells”, for contributions to this paper.
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