Understanding Tortuosity and Permeability variations in Naturally Fractured Reservoirs: Niobrara Formation

Tokan-Lawal, Adenike; Prodanović, Maša; Landry, Christopher J.; Eichhubl, Peter

doi:10.15530/urtec-2014-1922870

Cited by 8 publications

(3 citation statements)

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“…However, it must be mentioned that artificial "fractures" in lab-scale core sample are ideal due to the lack of roughness, tortuosity, and aperture variation. In fractured porous media, fractures will be more heterogeneous, and should these are taken into account (see for example the works by Tokan-Lawal et al, 2014;Laubach et al, 2010;and Becker et al, 2010) achieved permeability values after gel placement could be smaller compared to the ones reported in Tables 6 and 7. However, field applications pose several inherent challenges related to, among others, full wellbore control, fluids placement issues, unknown reservoir heterogeneities, three dimensional fluid flow, temperature variations in the direction away from the injection well, variations of ions type and concentration, fluids mixing especially at the front of the placed chemical system.…”

Section: Summary Of Core Scale Laboratory Experimentsmentioning

confidence: 97%

Laboratory Testing of Environmentally Friendly Chemicals for Water Management

Hatzignatiou

Askarinezhad²,

Giske

et al. 2015

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The goal of this work is to screen and evaluate laboratory mixtures of existing commercial, green sodium silicate chemicals that can be used for water management in carbonate naturally fractured (CNF) reservoirs. A thorough evaluation of a chemical for water management purposes requires the investigation of the chemical properties before, during, and after gelation. These properties are the gelant's viscosity, pH, filterability and injectivity, gelation time and kinetics of the gelation process, strength of the formed gel against applied external forces, gel stability, gel shrinkage, and post-gelation time behavior. This investigation has been conducted for different combinations (gelant systems) of sodium silicate with two types of polymers (a biopolymer and a synthetic polymer) along with a crosslinker.Measurements on the gelant systems viscosity showed that the base sodium silicate system has a low viscosity with a practically Newtonian behavior. Therefore, potential field placement difficulties may exist due to the lack of wellbore control with the possibility of the injected gellant reaching non-depleted formation regions; this can be partially addressed by improving the gelant's viscosity through the addition of polymers without sacrificing, or even increasing in some cases, the resulting gel strength. Gelant systems containing biopolymer resulted in a more shear-thinning behavior than other gelant systems, and the measured viscosity/shear-rate data could be well-matched with the Carreau model.Traditional tube testing and dynamic oscillatory tests, using an Anton-Paar MCR Rheometer, were performed to measure the gelation time and monitor the gelation process (initial viscous to viscoelastic state), and viscoelastic behavior of the formed gel at various temperatures. It was found that gelation time, a critical factor in the placement of the injected chemical system, can be tailored to field conditions by adjusting the gelant systems' contents and concentrations.The strength of the formed gels of various gelant systems were compared based on results from Maximum Compressional Pressure (MCP) tests. Strength tests showed promising gel behavior mainly for two of the selected gelant systems, one of which is the base system (sodium silicate without polymer additives) and the other is a silicate/biopolymer system. Silicate/synthetic-polymer, with or without crosslinker, systems yield significantly weaker gels. More detailed investigations are needed mostly on the interpretation of the tests to be able to upscale the laboratory results to field applications.In addition to bulk measurements, core flood tests were also conducted in artificially fractured carbonate cores to investigate gel isolation effectiveness, as well as formed gel stability and shrinkage at static gelation conditions. Although some shrinkage was observed over time in practically all core-scale experiments, the resulting core average permeabilities in post-gelation floods were significantly lower than the original fracture rock sample permeability;...

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Section: Summary Of Core Scale Laboratory Experimentsmentioning

confidence: 97%

Laboratory Testing of Environmentally Friendly Chemicals for Water Management

Hatzignatiou

Askarinezhad²,

Giske

et al. 2015

All Days

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“…An average density range was calculated for each hydrogeological unit according to the rock types identified in the borehole cuttings. The third of these parameters was the tortuosity (α), defined as a ratio of fluid flow in a porous media (Pisani, 2011;Tokan-Lawal et al, 2014). For this study, the value of α was fixed at 1.4 (Urish, 1981;Aguilera, 2008;Piedrahita and Aguilera, 2017) for all the hydrogeological units due to its low impact in zones with low porosity, a primary characteristic of this catchment.…”

Section: Claymentioning

confidence: 99%

Quantification of groundwater storage heterogeneity in weathered/fractured basement rock aquifers using electrical resistivity tomography: Sensitivity and uncertainty associated with petrophysical modelling

González

Comte

Legchenko

et al. 2021

Journal of Hydrology

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Quantifying groundwater storage in weathered/fractured basement rock aquifers can be challenging owing to both their high degree of heterogeneity and their overall low storage capacity.Therefore, in these aquifers, the use of direct borehole hydraulic data is usually insufficient. Here we assessed the popular method of electrical resistivity tomography (ERT), combined with borehole data and including associated uncertainties, to resolve the spatial variability of groundwater storage properties at high resolution within a fractured mica schist aquifer in Ireland. Porosity distributions across both the saturated and unsaturated zones were calculated from two-dimensional (2D) ERT resistivities using two standard petrophysical models, Archie and Waxman & Smits (WS), the latter accounting for the influence of clay minerals on resistivity data. Our results demonstrated the importance of the hydrogeological conceptual constraints provided by ERT when parametrizing the 2D petrophysical models from borehole point data. They also confirmed the importance of accounting for clay minerals (the products of bedrock weathering processes) in the WS model, whereas predictions from Archie's model produced unrealistically high porosity values of over an order of magnitude higher than the WS model. The WS model predicted porosities decreasing exponentially with depth, with values ranging from a few % in the shallowest, most-weathered part of the bedrock (upper 5 m on average) and deep fractured zones (to about 20 m deep), to less than 1% in the underlying fissured aquifer, and possibly down another order of magnitude in the deep massive bedrock. WS-derived porosities were in agreement with independent vertical water content profiles derived from magnetic resonance sounding (MRS), as well as point storativity values estimated from borehole hydraulic testing at the study site, with particularly good matches in the upper weathered/fractured bedrock and deeply weathered/fractured zones associated with regional faults.Detailed comparison suggested that WS provides an upper-bound estimate of groundwater storage in this environment. In the deep massive, un-weathered, and poorly fractured bedrock, however, discrepancies between groundwater storage estimate obtained from the three methods (ERT, MRS, and hydraulic) prevented reliable storage quantification, owing to the methods' inherent technical limitations in such low porosity rocks. Our results demonstrated the suitability of resistivity tomography to quantify groundwater storage heterogeneity in weathered/fractured basement rock aquifers at high resolution and with reasonable overall uncertainty given the relative high uncertainties in petrophysical parameters at the kilometric scale. The results are promising for better characterization of groundwater storage variations in these hydrogeological systems, which are crucial to predict their response to climate variability and human exploitation.

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“…The limitation of these empirical correlations is that the coefficients are empirical and vary with rock type. Tokan-Lawal et al (2014) captured the fracture geometry with x-ray microtomograpgy (CT) scan and determined the permeability and tortuosity of the fracture by cubic law equation (Eq. 4 in the following section).…”

Section: Introductionmentioning

confidence: 99%

A new correlation to evaluate the fracture permeability changes as reservoir is depleted

Ling

Pei

et al. 2016

Journal of Petroleum Science and Engineering

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The increasing development of unconventional resources plays an important role in filling the gap between demand and conventional oil and gas supply. Due to the nature of low permeability, tight gas and shale reservoirs need fractures, natural and artificial, to produce hydrocarbon at commercial rates. Fracture permeability is a key factor affecting the development of these unconventional reservoirs. It is observed that fracture permeabilities decline as reservoirs are depleted because pore pressure declines lead to the closures of fractures and the permeability reductions. Therefore a correlation to quantify the variations of the fracture permeability with pore pressure is highly needed. In this study we investigate the effects of pore pressures on fracture permeabilities assuming constant in-situ stresses exert on the formations. Starting from the force balance, we derived equations to calculate fracture permeability based on fracture geometry. Our new correlations can also be used to evaluate the changing fracture permeability during the recovery of hydrocarbon. The proposed correlations provide a way to estimate the fracture permeability at initial pressure and the depleted pressure at any production stage. Although some experiments had been conducted to build relationships between fracture permeability and pressure for some types of rocks. It is noted that experiments are time

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Understanding Tortuosity and Permeability variations in Naturally Fractured Reservoirs: Niobrara Formation

Cited by 8 publications

References 0 publications

Laboratory Testing of Environmentally Friendly Chemicals for Water Management

Laboratory Testing of Environmentally Friendly Chemicals for Water Management

Quantification of groundwater storage heterogeneity in weathered/fractured basement rock aquifers using electrical resistivity tomography: Sensitivity and uncertainty associated with petrophysical modelling

A new correlation to evaluate the fracture permeability changes as reservoir is depleted

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