Open Access

ARTICLE

Numerical Investigation of Stress and Toughness Contrast Effects on the Vertical Propagation of Fluid-Driven Fractures in Shale Reservoirs

Manqing Qian^*, Xiyu Chen, Yongming Li

State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, 610500, China

* Corresponding Author: Manqing Qian. Email:

(This article belongs to the Special Issue: Fluid and Thermal Dynamics in the Development of Unconventional Resources II)

Fluid Dynamics & Materials Processing 2025, 21(6), 1353-1377. https://doi.org/10.32604/fdmp.2025.061652

Received 29 November 2024; Accepted 13 March 2025; Issue published 30 June 2025

Abstract

Shale reservoirs are characterized by numerous geological discontinuities, such as bedding planes, and exhibit pronounced heterogeneity across rock layers separated by these planes. Bedding planes often possess distinct mechanical properties compared to the surrounding rock matrix, particularly in terms of damage and fracture behavior. Consequently, vertical propagation of hydraulic fractures is influenced by both bedding planes and the heterogeneity. In this study, a numerical investigation into the height growth of hydraulic fractures was conducted using the finite element method, incorporating zero-thickness cohesive elements. The analysis explored the effects of bedding planes, toughness contrasts between layers, and variations in in-situ stress across different strata. The results reveal that hydraulic fractures are more likely to propagate along bedding planes instead of traversing them and extending vertically into barrier layers when (1) bedding strength is low, (2) stress contrast between layers is high, and (3) toughness contrast is significant. Furthermore, for a given bedding strength, increased stress contrast or higher toughness contrast between layers elevate hydraulic fracture extension pressure. When a substantial stress difference exists between layers (L_c = 0.4), hydraulic fractures preferentially propagate along bedding planes. Conversely, as bedding strength increases, the propagation distance along bedding planes decreases, accompanied by an amplified horizontal compressive stress field. Notably, when the stress difference is sufficiently small (SD < −0.2), a phenomenon termed “stress rolling” emerges, wherein hydraulic fractures deviate from vertical growth and instead extend along a near-horizontal trajectory.

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