Open Access

ARTICLE

The Influence of Acid on the Rock Mechanical Characteristics of Deep Shale in the Wujiaping Formation

by Hao Zhang¹, Yan Zhang^1,*, Wei Liu², Ximin Zhang³, Xiang Liu²

1 School of Petroleum Engineering, Yangtze University, Wuhan, 430100, China
2 Petroleum Engineering Technology Research Institute, Jianghan Oilfield Branch of Sinopec, Wuhan, 430035, China
3 Drilling Technology Research Institute, Sinopec Shengli Oilfield Service Corporation, Deyang, 618000, China

* Corresponding Author: Yan Zhang. Email:

Energy Engineering 2024, 121(1), 27-42. https://doi.org/10.32604/ee.2023.041410

Received 21 April 2023; Accepted 29 June 2023; Issue published 27 December 2023

Abstract

The microscopic characteristics and mechanical properties of rocks change after the action of acid on deep shale, which affects the fracturing effect. Accordingly, we designed and conducted indoor experiments related to the changes in macro and microscopic characteristics after the interaction of acid with the shale of Wujiaping Formation, based on which the characteristic law of fracture volume modification after acid fracturing was studied using numerical simulation. The results demonstrate that the pores and fractures are enlarged and the structure is significantly loosened after the acid immersion. And a 15% concentration of hydrochloric acid can effectively dissolve shale. Furthermore, the degree of acid-etching reaction is highly variable because of the different carbonate content, which reveals the strong inhomogeneity of the shale system in the Wujiaping Group reservoir section. After the acid interacted with the shale rock samples, the triaxial compressive strength, elastic modulus, and Poisson’s ratio of shale decreased. Moreover, the evaluation of the effect after acid fracturing simulated by fracturing software revealed that the smaller the value of elastic modulus in shale-based reservoirs, the more favorable the fracture volume modification. This discovery not only provides a theoretical basis for the expansion and extension patterns of acid-fracturing in carbonaceous shale formations but also offers research methods and theoretical insights for the fundamental exploration of other deep-seated oil and gas resources.

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