Combined Effect of Pore Water Overpressure, Far-Field Stresses, and Strength Parameters in Wellbore Stability

Deangeli, Chiara; Marchelli, Maddalena

doi:10.3389/feart.2022.860818

Cited by 3 publications

(2 citation statements)

References 62 publications

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“…Further developments could investigate more deeply the distributions of the input variable or the method could be extended also to rigid barriers [23,24] or even embankments [25].…”

Section: Discussionmentioning

confidence: 99%

A time-independent reliability based design approach for debris flow flexible barriers

Marchelli,

Deangeli

2023

E3S Web of Conf.

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The design of debris flow protective structures has represented a challenge since the last decades. The design process might consider several variables related to actions and resistances, mainly linked to impact pressure and dynamic pressure resistance. Debris flow events do not have always the same magnitude, and small events can occur with a high probability. Therefore, an events frequency-magnitude relationship might be considered in the design of protective structures. In the Eurocodes framework, the fixed partial safety factors design approach not considering the intrinsic site variability of these phenomena, does not allow obtaining a specific probability of failure. Reliability-based approaches reveal to be compelling solutions. Focusing on flexible barriers, the paper presents a novel time-independent reliability approach, which considers all the possible debris flow events and provides the failure probability of a barrier in a given temporal interval.

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“…Further developments could investigate more deeply the distributions of the input variable or the method could be extended also to rigid barriers [23,24] or even embankments [25].…”

Section: Discussionmentioning

confidence: 99%

A time-independent reliability based design approach for debris flow flexible barriers

Marchelli,

Deangeli

2023

E3S Web of Conf.

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“…The determination of the shale mechanical properties at large depth is still a problem. An accurate assessment of rock mechanical properties is through laboratory tests; however, core retrieval at large depths can be a difficult task [18]. In fact, shale cores can be subject to alteration as they are retrieved from the subsurface due to changes in pressure, temperature and oxidation state [19].…”

Section: Introductionmentioning

confidence: 99%

Sensitivity Analysis of Wellbore Mud Pressure towards Anisotropic Shale Properties, Pore Fluid Pressure and Far Field Stresses

Deangeli,

Liu,

Yang

2023

Applied Sciences

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The paper investigates the mud pressure to maintain the stability of wellbores drilled in transversely isotropic shale through sensitivity analyses, carried out with analytical and numerical modeling (FLAC). To this end, we interpreted the anisotropic strength of the Tournemire shale with the Weakness Plane Model (WPM) and the modified Hoek–Brown criterion (HBm). The sensitivity analyses of synthetic case studies indicated a different trend in mud pressure for the two criteria. In some cases, the WPM predicts mud pressures higher than those predicted by the HBm and vice versa. The mud pressures predicted by the HBm resulted in being more sensitive to the increase in the anisotropy of the far field stresses for all the inclinations of the weakness planes. In this context, the WPM predicts some anomalous low mud pressures in a wide range of inclinations of the weak planes. The change in the frictional component of strength decreases with an increase in the pore fluid pressure for both criteria. The mud pressure predicted by the WPM resulted in being more sensitive to the change in frictional strength. The change in trend of the two criteria with change in input data suggests caution in the “a priori” selection of the strength criterion. A simple solution is proposed to predict a safe and reliable mud pressure with a small number of lab tests.

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Comparison of Mud Pressures Predicted with Different Constitutive Models in Anisotropic Shale Rocks

Liu,

Deangeli,

Martinelli

2024

SPE Europe Energy Conference and Exhibition

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Depleted oil and gas fields are good targets for gas storage both in offshore and onshore environments. Carbon capture and sequestration (CCS) must repurpose existing rigs to drill new wells cost-effectively. The integrity of the well is crucial for successful carbon dioxide sequestration. During the drilling phase, well integrity involves preventing not uniform wellbore wall geometry induced by local rock failures and ensuring that cave-ins and washouts do not occur. The post-drilling experience in depleted fields can undoubtedly help selecting mud pressures to avoid instability when drilling new wells. The cap of most depleted fields is composed of shale rock that often exhibits variation in strength properties along and across the lamination planes and has been responsible for the major source of instability [Carey & Torsæter, 2019; Mehrabian et al., 2019]. The mechanical properties of shale at significant depths are hard to ascertain [Steiger & Leung, 1992]. Although laboratory tests provide accurate assessments, retrieving cores from deep wells is challenging due to potential alterations during retrieval and specimen preparation. Shale cores can undergo changes in pressure, temperature, and oxidation state as they are brought to the surface, which can affect their properties [Basu et al., 2020]. Cores retrieved from wells may be limited and damaged, making it difficult to obtain reliable mechanical property data directly from them [Josh et al., 2012]. Alternatively, mechanical properties can be obtained from laboratory tests conducted on outcropping formations similar to those found in the subsurface [Risnes, 2001]. Mechanical properties at depth are often inferred indirectly using correlations with log data and microscopic models [Abousleiman et al., 2007, Woehrl et al., 2010]. These correlations are empirical equations used to establish continuous profiles of elastic constants and strength parameters (Mandal et al. 2021]. Empirical relationships derived from log data are typically valid within specific geological settings, reflecting the conditions of the region where they were established. Additionally, the transverse isotropy of shale, a common characteristic in many formations, is often not specifically addressed in indirect approaches. This can lead to challenges in accurately characterizing the mechanical behavior of shale formations, particularly in situations where transverse isotropy significantly influences rock behavior. The low permeability of saturated shale rock indeed has implications for wellbore stability, especially immediately after drilling. When drilling through shale formations, the drilling process can disturb the equilibrium of pore fluid pressure within the rock, leading to undrained conditions in the short term. The undrained pore fluid pressure evolution can enhance plasticity around the wellbore [Asaka & Holt 2021; Vales et al. 2004; Aoki et al., 1993; Holt et al. 2014; Detournay & Atkinson, 2000; Deangeli & Marchelli, 2022; Tran et al., 2022]. All the previous considerations evidenced the difficulty and uncertainties related to the prediction of mud pressures in wellbore drilled in transversely isotropic shales. To reduce uncertainties on mud pressure prediction, there is the need of properly investigate the mechanical response of anisotropic shales during drilling operations. By integrating multiple models, engineers can gain a deeper understanding of the complex interactions between different factors influencing shale behavior. This enables them to anticipate potential challenges and hazards during drilling and wellbore operations, leading to more proactive risk mitigation strategies.

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Combined Effect of Pore Water Overpressure, Far-Field Stresses, and Strength Parameters in Wellbore Stability

Cited by 3 publications

References 62 publications

A time-independent reliability based design approach for debris flow flexible barriers

A time-independent reliability based design approach for debris flow flexible barriers

Sensitivity Analysis of Wellbore Mud Pressure towards Anisotropic Shale Properties, Pore Fluid Pressure and Far Field Stresses

Comparison of Mud Pressures Predicted with Different Constitutive Models in Anisotropic Shale Rocks

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