Effects of combined dynamic-static loading and acidic corrosion treatment on the mechanical properties and microstructure of shale

Abstract

A critical scientific gap exists in quantifying the intrinsic mechanisms of shale mechanical property degradation induced by the combined effects of perforation (impact) and acidization—two core techniques for shale reservoir permeability enhancement. To address this gap, this study proposed an innovative coupled experimental framework integrating dynamic-static cyclic loading (to simulate perforation impact) and acid erosion. Static uniaxial compression tests were performed on treated damaged shale samples, with microstructural characterization via X-ray diffraction (XRD) and scanning electron microscopy (SEM). Key findings include: (1) The damage factor (characterized by longitudinal wave velocity) showed a significant positive correlation with acid concentration; (2) Combined damage (impact + acidization) caused far more severe mechanical deterioration than single damage modes—for instance, samples under combined damage with 20% hydrochloric acid exhibited a strength reduction to 158.97 MPa, with sharp decreases in peak strength and elastic modulus; (3) Damage reduced total energy and elastic strain energy of samples while increasing dissipated energy proportion, leading to more developed internal fractures and severe failure in combined damage samples; (4) Acidization promoted sample fragmentation into smaller debris, resulting in significantly higher fractal dimensions of acidized shale than other damage types under the same acid concentration; (5) XRD and SEM analyses confirmed that high-concentration acid erosion reduced shale carbonate content, and the synergy of mechanical pre-damage and chemical dissolution in combined damage accelerated acid-rock reactions, significantly increasing micro-interfacial pores and degrading shale structural integrity. This study’s innovation lies in establishing a coupled experimental framework that reproduces the actual ‘‘perforation-acidization” sequence, quantitatively revealing the synergistic degradation mechanism of shale mechanical properties under combined damage—providing a novel theoretical basis for optimizing shale reservoir stimulation parameters.

Keywords

Shale / Acid treatment / Combined damage / Energy dissipation / Microstructure

CRediT authorship contribution statement

Kang Peng: Resources, Funding acquisition. Hankuo Zhang: Project administration, Formal analysis. Mao Jing: Writing – original draft, Methodology. Yunge Zhao: Validation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was funded by the National Natural Science Foundation of China (No. 52474120), the National Key Research and Development Program of China — 2023 Key Special Project (No. 2023YFC2907400), the Fundamental Research Funds for the Central Universities (No. 2023CXQD045), and the Hunan Provincial Natural Science Foundation for Distinguished Young Scholars (No. 2023JJ10072).

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