Impact of stress regime change on the permeability of a naturally fractured carbonate buildup (Latemar, the Dolomites, northern Italy)

IF 3.2 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS Solid Earth Pub Date : 2024-07-08 DOI:10.5194/se-15-763-2024
Onyedika Anthony Igbokwe, Jithender J. Timothy, Ashwani Kumar, Xiao Yan, Mathias Mueller, Alessandro Verdecchia, Günther Meschke, Adrian Immenhauser
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Abstract

Abstract. Changing stress regimes control fracture network geometry and influence porosity and permeability in carbonate reservoirs. Using outcrop data analysis and a displacement-based linear elastic finite-element method, we investigate the impact of stress regime change on fracture network permeability. The model is based on fracture networks, specifically fracture substructures. The Latemar, predominantly affected by subsidence deformation and Alpine compression, is taken as an outcrop analogue for an isolated (Mesozoic) carbonate buildup with fracture-dominated permeability. We apply a novel strategy involving two compressive boundary loading conditions constrained by the study area's NW–SE and N–S stress directions. Stress-dependent heterogeneous apertures and effective permeability were computed in the 2D domain by (i) using the local stress state within the fracture substructure and (ii) running a single-phase flow analysis considering the fracture apertures in each fracture substructure. Our results show that the impact of the modelled far-field stresses at (i) subsidence deformation from the NW–SE and (ii) Alpine deformation from N–S increased the overall fracture aperture and permeability. In each case, increasing permeability is associated with open fractures parallel to the orientation of the loading stages and with fracture densities. The anisotropy of permeability is increased by the density and connectedness of the fracture network and affected by shear dilation. The two far-field stresses simultaneously acting within the selected fracture substructure at a different magnitude and orientation do not necessarily cancel each other out in the mechanical deformation modelling. These stresses affect the overall aperture and permeability distributions and the flow patterns. These effects – potentially ignored in simpler stress-dependent permeability – can result in significant inaccuracies in permeability estimation.
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应力机制变化对天然断裂碳酸盐堆积层渗透性的影响(意大利北部多洛米蒂山脉的拉特马尔)
摘要应力体系的变化控制着碳酸盐岩储层的断裂网几何形状,并影响着碳酸盐岩储层的孔隙度和渗透率。利用露头数据分析和基于位移的线性弹性有限元方法,我们研究了应力机制变化对裂缝网络渗透率的影响。该模型基于断裂网络,特别是断裂子结构。主要受沉降变形和阿尔卑斯山压缩影响的拉特玛尔地区,被视为具有以断裂为主的渗透性的孤立(中生代)碳酸盐岩堆积的露头模拟区域。我们采用了一种新颖的策略,其中包括受研究区域西北-东南和北-南应力方向制约的两个压缩边界加载条件。通过(i)使用断裂子结构内的局部应力状态和(ii)考虑每个断裂子结构中的断裂孔隙运行单相流分析,在二维域中计算了与应力相关的异质孔隙和有效渗透率。结果表明,在(i) 西北-东南方向的下沉变形和(ii) 南北方向的阿尔卑斯山变形时,模拟远场应力的影响增加了整个断裂孔径和渗透率。在每种情况下,渗透率的增加都与平行于加载阶段方向的开放裂缝和裂缝密度有关。渗透率的各向异性因断裂网络的密度和连通性而增加,并受剪切扩张的影响。在力学变形模型中,同时作用于所选断裂子结构内的两个不同大小和方向的远场应力不一定会相互抵消。这些应力会影响整体孔径和渗透率分布以及流动模式。这些影响--在简单的应力相关渗透率中可能被忽略--会导致渗透率估算的严重误差。
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来源期刊
Solid Earth
Solid Earth GEOCHEMISTRY & GEOPHYSICS-
CiteScore
6.90
自引率
8.80%
发文量
78
审稿时长
4.5 months
期刊介绍: Solid Earth (SE) is a not-for-profit journal that publishes multidisciplinary research on the composition, structure, dynamics of the Earth from the surface to the deep interior at all spatial and temporal scales. The journal invites contributions encompassing observational, experimental, and theoretical investigations in the form of short communications, research articles, method articles, review articles, and discussion and commentaries on all aspects of the solid Earth (for details see manuscript types). Being interdisciplinary in scope, SE covers the following disciplines: geochemistry, mineralogy, petrology, volcanology; geodesy and gravity; geodynamics: numerical and analogue modeling of geoprocesses; geoelectrics and electromagnetics; geomagnetism; geomorphology, morphotectonics, and paleoseismology; rock physics; seismics and seismology; critical zone science (Earth''s permeable near-surface layer); stratigraphy, sedimentology, and palaeontology; rock deformation, structural geology, and tectonics.
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