Pressure-Dependent Natural-Fracture Permeability in Shale and Its Effect on Shale-Gas Well Production
01 May 2013-Spe Reservoir Evaluation & Engineering (Society of Petroleum Engineers)-Vol. 16, Iss: 02, pp 216-228
About: This article is published in Spe Reservoir Evaluation & Engineering.The article was published on 2013-05-01. It has received 276 citations till now. The article focuses on the topics: Oil shale & Permeability (earth sciences).
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TL;DR: In this article, the authors present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization, orientation, and size patterns, and identify a need for further work in this field and on the role of natural fractures generally.
Abstract: Natural fractures have long been suspected as a factor in production from shale reservoirs because gas and oil production commonly exceeds the rates expected from low-porosity and low-permeability shale host rock. Many shale outcrops, cores, and image logs contain fractures or fracture traces, and microseismic event patterns associated with hydraulic-fracture stimulation have been ascribed to natural fracture reactivation. Here we review previous work, and present new core and outcrop data from 18 shale plays that reveal common types of shale fractures and their mineralization, orientation, and size patterns. A wide range of shales have a common suite of types and configurations of fractures: those at high angle to bedding, faults, bed-parallel fractures, early compacted fractures, and fractures associated with concretions. These fractures differ markedly in their prevalence and arrangement within each shale play, however, constituting different fracture stratigraphies—differences that depend on interface and mechanical properties governed by depositional, diagenetic, and structural setting. Several mechanisms may act independently or in combination to cause fracture growth, including differential compaction, local and regional stress changes associated with tectonic events, strain accommodation around large structures, catagenesis, and uplift. Fracture systems in shales are heterogeneous; they can enhance or detract from producibility, augment or reduce rock strength and the propensity to interact with hydraulic-fracture stimulation. Burial history and fracture diagenesis influence fracture attributes and may provide more information for fracture prediction than is commonly appreciated. The role of microfractures in production from shale is currently poorly understood yet potentially critical; we identify a need for further work in this field and on the role of natural fractures generally.
709 citations
TL;DR: The results from an ongoing laboratory study investigating petrophysical characteristics of the Montney and Bakken formations in Canada are presented in this article, where the pore network (porosity, pore size distribution, and fluid transport permeability) properties of these formations in areas with limited datasets are analyzed.
187 citations
TL;DR: In this paper, a simulation model was constructed for CO2 flooding and huff and puff in the Marcellus and New Albany shale fields to examine the effects of CO2 injection to enhanced gas recovery (EGR) and CO2 storage.
151 citations
TL;DR: In this paper, the authors provide an overview of the challenges associated with evaluating key reservoir and hydraulic fracture properties and discuss recent advances in the area of shale gas reservoir and fracture characterization.
128 citations
TL;DR: The potential of CO2 as an alternative working fluid, both in fracturing and re-stimulating activities, beyond its environmental advantages is discussed, as part of the themed issue ‘Energy and the subsurface’.
Abstract: Despite the impact that hydraulic fracturing has had on the energy sector, the physical mechanisms that control its efficiency and environmental impacts remain poorly understood in part because the length scales involved range from nanometres to kilometres. We characterize flow and transport in shale formations across and between these scales using integrated computational, theoretical and experimental efforts/methods. At the field scale, we use discrete fracture network modelling to simulate production of a hydraulically fractured well from a fracture network that is based on the site characterization of a shale gas reservoir. At the core scale, we use triaxial fracture experiments and a finite-discrete element model to study dynamic fracture/crack propagation in low permeability shale. We use lattice Boltzmann pore-scale simulations and microfluidic experiments in both synthetic and shale rock micromodels to study pore-scale flow and transport phenomena, including multi-phase flow and fluids mixing. A mechanistic description and integration of these multiple scales is required for accurate predictions of production and the eventual optimization of hydrocarbon extraction from unconventional reservoirs. Finally, we discuss the potential of CO2 as an alternative working fluid, both in fracturing and re-stimulating activities, beyond its environmental advantages.This article is part of the themed issue 'Energy and the subsurface'.
113 citations
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References
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TL;DR: In this paper, the results of many years of research on joint properties are synthesized in a coupled joint behaviour model, which simulates stress and size-dependent coupling of shear stress, diplacement, dilation and conductivity.
1,269 citations
TL;DR: In this article, the authors characterized natural fractures in four Barnett Shale cores in terms of orientation, size, and sealing properties, and they measured a mechanical rock property, the subcritical crack index, which governs fracture pattern development.
Abstract: Gas production from the Barnett Shale relies on hydraulic fracture stimulation. Natural opening-mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone. Knowledge of both the present-day maximum horizontal stress, which controls the direction of hydraulic fracture propagation, and the geometry of the natural fracture system, which we discuss here, is therefore necessary for effective hydraulic fracture treatment design. We characterized natural fractures in four Barnett Shale cores in terms of orientation, size, and sealing properties. We measured a mechanical rock property, the subcritical crack index, which governs fracture pattern development. Natural fractures are common, narrow (0.05 mm; 0.002 in.), sealed with calcite, and present in en echelon arrays. Individual fractures have high length/width aspect ratios (1000:1). They are steep (75), and the dominant trend is west-northwest. Other sets trend north-south. The narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability, but the population may follow a power-law size distribution where the largest fractures are open. The subcritical crack index for the Barnett Shale is high, indicating fracture clustering, and we suggest that large open fractures exist in clusters spaced several hundred feet apart. These fracture clusters may enhance permeability locally, but they may be problematic for hydraulic fracture treatments. The smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments. Because the maximum horizontal stress trends northeast-southwest and is nearly normal to the dominant natural fractures, reactivation widens the treatment zone along multiple strands.
954 citations
TL;DR: In this article, two computer codes, TOUGH2 and FLAC3D, are linked and jointly executed for coupled thermal-hydrologic-mechanical (THM) analysis of multiphase fluid flow, heat transfer, and deformation in fractured and porous rock.
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