http://earthwise-staging.bgs.ac.uk/index.php?action=history&feed=atom&title=OR%2F15%2F066_Fracture_propagationOR/15/066 Fracture propagation - Revision history2026-04-17T08:06:54ZRevision history for this page on the wikiMediaWiki 1.42.3http://earthwise-staging.bgs.ac.uk/index.php?title=OR/15/066_Fracture_propagation&diff=44313&oldid=prevAjhil at 12:45, 3 December 20192019-12-03T12:45:29Z<p></p>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>===Fracture height===</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>===Fracture height===</div></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Fisher, King and Warpinski (Fisher & Warpinski, 2011<ref name="Fisher 2011">Fisher, K, and Warpinski, N. (2011). Hydraulic fracture-height growth: real data. Paper SPE 145949 presented at the ''Annual Technical Conference and Exhibition of the Society of Petroleum Engineers'', Denver, Colorado. DOI: 10.2118/145949-MS</ref>; King, 2012<ref name="King 2012">King, G E. (2012). Hydraulic fracturing 101: what every representative, environmentalist, regulator, reporter, investor, university researcher, neighbours and engineer should know about estimating frac risk and improving frac performance in unconventional gas and oil wells. ''Society of Petroleum Engineers''. Hydraulic Fracturing Technology; Woodlands, TX, 2012.</ref>) have published the most comprehensive research on observations of hydraulic fracturing during shale gas exploitation. They used microseismic data from thousands of fracture treatments carried out on the Barnett, Woodford, Marcellus and Eagle Ford Shale formations; these being some of the highest producing formations in North America. The largest vertical fracture observed had a vertical extent of 1,500 feet (457 metres<del style="font-weight: bold; text-decoration: none;"><ref name="Davies 2012">Davies et al. (2012) report 588 metres in Barnett shale</ref></del>) and occurred in the Marcellus shale. The largest mapped fractures tended to occur at the greatest depths. Fisher & Warpinski speculate that these are associated with the interaction with natural fractures. They observed that fractures grow much taller in the Marcellus than in the Barnett.</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Fisher, King and Warpinski (Fisher & Warpinski, 2011<ref name="Fisher 2011">Fisher, K, and Warpinski, N. (2011). Hydraulic fracture-height growth: real data. Paper SPE 145949 presented at the ''Annual Technical Conference and Exhibition of the Society of Petroleum Engineers'', Denver, Colorado. DOI: 10.2118/145949-MS</ref>; King, 2012<ref name="King 2012">King, G E. (2012). Hydraulic fracturing 101: what every representative, environmentalist, regulator, reporter, investor, university researcher, neighbours and engineer should know about estimating frac risk and improving frac performance in unconventional gas and oil wells. ''Society of Petroleum Engineers''. Hydraulic Fracturing Technology; Woodlands, TX, 2012.</ref>) have published the most comprehensive research on observations of hydraulic fracturing during shale gas exploitation. They used microseismic data from thousands of fracture treatments carried out on the Barnett, Woodford, Marcellus and Eagle Ford Shale formations; these being some of the highest producing formations in North America. The largest vertical fracture observed had a vertical extent of 1,500 feet (457 metres) and occurred in the Marcellus shale. The largest mapped fractures tended to occur at the greatest depths. Fisher & Warpinski speculate that these are associated with the interaction with natural fractures. They observed that fractures grow much taller in the Marcellus than in the Barnett.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Fisher & Warpinski (2011)<ref name="Fisher 2011"></ref> present tiltmeter data from more than 10&nbsp;000 fractures and examine the vertical and horizontal components of these fractures. The overall pattern is that fractures shallower than 4,000 feet (1,200 metres) are predominantly vertical whereas below this point the ratio between vertical and horizontal fracture growth is more complex. Fisher & Warpinski (2011)<ref name="Fisher 2011"></ref> discuss these patterns and conclude that the ''in situ ''stress and mechanical properties of the stratigraphy, such as variations in moduli and anisotropy associated with laminations, are the reasons why vertical fractures are hindered and lateral fracture growth is the preferred path of least resistance. Outside factors such as large faults in the area can lead to an increase in vertical fracture growth. This complex data set goes to show the complexities associated with fracture development and the mechanics driving fracture propagation in a heterogeneous layered rock.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Fisher & Warpinski (2011)<ref name="Fisher 2011"></ref> present tiltmeter data from more than 10&nbsp;000 fractures and examine the vertical and horizontal components of these fractures. The overall pattern is that fractures shallower than 4,000 feet (1,200 metres) are predominantly vertical whereas below this point the ratio between vertical and horizontal fracture growth is more complex. Fisher & Warpinski (2011)<ref name="Fisher 2011"></ref> discuss these patterns and conclude that the ''in situ ''stress and mechanical properties of the stratigraphy, such as variations in moduli and anisotropy associated with laminations, are the reasons why vertical fractures are hindered and lateral fracture growth is the preferred path of least resistance. Outside factors such as large faults in the area can lead to an increase in vertical fracture growth. This complex data set goes to show the complexities associated with fracture development and the mechanics driving fracture propagation in a heterogeneous layered rock.</div></td></tr>
</table>Ajhilhttp://earthwise-staging.bgs.ac.uk/index.php?title=OR/15/066_Fracture_propagation&diff=44312&oldid=prevAjhil at 12:39, 3 December 20192019-12-03T12:39:55Z<p></p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 13:39, 3 December 2019</td>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Cosgrove (1995)<ref name="Cosgrove 1995">Cosgrove, J W. (1995). The expression of hydraulic fracturing in rocks and sediments. In: ''Fractography: Fracture Topography as a Tool in Fracture Mechanics and Stress Analysis''. Geological Society Special Publication No.'''92''', pp.187–196.</ref> showed that natural hydraulic fractures can be observed in outcrops from the centimetre to metre scale. There are several types of natural hydraulic fracture that have all been extensively studied, including: injectities (e.g. Hurst ''et al.'', 2011<ref name="Hurst 2011">Hurst, A, Scott, A, and Vigorito, M. (2011). Physical characteristics of sand injectites. ''Earth Science Reviews'', 106, pp.215–246.</ref>), igneous dykes (e.g. Polteau ''et al.'', 2008<ref name="Polteau 2008">Polteau, S, Mazzini, A, Galland, O, Planke, S, and Malthe-Sørenssen, A. (2008). Saucershaped intrusions: occurrences, emplacement and implications. ''Earth and Planetary Science Letters'', '''266''', pp.195–204.</ref>), veins (e.g. Cosgrove, 1995<ref name="Cosgrove 1995"></ref>), coal cleats (e.g. Laubach ''et al.'', 1998<ref name="Laubach 1998">Laubach, S E, Marrett, R A, Olson, J E, and Scott, A R. (1998). Characteristics and origins of coal cleat: a review. ''International Journal of Coal Geology'', 35, pp.175–207.</ref>), and joints (e.g. McConaughy & Engelder, 1999<ref name="McConaughy 1999">McConaughy, D T, and Engelder, T. (1999). Joint interaction with embedded concretions: joint loading configurations inferred from propagation paths. ''Journal of Structural Geology'', 21, pp.1637–1652.</ref>). Savalli & Engelder (2005)<ref name="Savalli 2005"></ref> showed that growth of natural hydraulic fractures could be studied in the Devonian Marcellus formation in the US on the basis of plume lines that occur over a range of scales from centimetre to metre scale. The formation of these natural features is inferred to derive from gas diffusion and expansion within the shale during multiple propagation events.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Cosgrove (1995)<ref name="Cosgrove 1995">Cosgrove, J W. (1995). The expression of hydraulic fracturing in rocks and sediments. In: ''Fractography: Fracture Topography as a Tool in Fracture Mechanics and Stress Analysis''. Geological Society Special Publication No.'''92''', pp.187–196.</ref> showed that natural hydraulic fractures can be observed in outcrops from the centimetre to metre scale. There are several types of natural hydraulic fracture that have all been extensively studied, including: injectities (e.g. Hurst ''et al.'', 2011<ref name="Hurst 2011">Hurst, A, Scott, A, and Vigorito, M. (2011). Physical characteristics of sand injectites. ''Earth Science Reviews'', 106, pp.215–246.</ref>), igneous dykes (e.g. Polteau ''et al.'', 2008<ref name="Polteau 2008">Polteau, S, Mazzini, A, Galland, O, Planke, S, and Malthe-Sørenssen, A. (2008). Saucershaped intrusions: occurrences, emplacement and implications. ''Earth and Planetary Science Letters'', '''266''', pp.195–204.</ref>), veins (e.g. Cosgrove, 1995<ref name="Cosgrove 1995"></ref>), coal cleats (e.g. Laubach ''et al.'', 1998<ref name="Laubach 1998">Laubach, S E, Marrett, R A, Olson, J E, and Scott, A R. (1998). Characteristics and origins of coal cleat: a review. ''International Journal of Coal Geology'', 35, pp.175–207.</ref>), and joints (e.g. McConaughy & Engelder, 1999<ref name="McConaughy 1999">McConaughy, D T, and Engelder, T. (1999). Joint interaction with embedded concretions: joint loading configurations inferred from propagation paths. ''Journal of Structural Geology'', 21, pp.1637–1652.</ref>). Savalli & Engelder (2005)<ref name="Savalli 2005"></ref> showed that growth of natural hydraulic fractures could be studied in the Devonian Marcellus formation in the US on the basis of plume lines that occur over a range of scales from centimetre to metre scale. The formation of these natural features is inferred to derive from gas diffusion and expansion within the shale during multiple propagation events.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The tallest example of natural hydraulic fracture result when they cluster and form chimneys (also termed pipes or blowout pipes). These have been observed to extend vertically for hundreds of metres (e.g. Cartwright ''et al.'', 2007<ref name="Cartwright 2007">Cartwright, J, Huuse, M, and Aplin, A. (2007). Seal bypass systems. ''American Association of Petroleum Geologists Bulletin'', 91, pp.1141–1166.</ref>; Huuse ''et al.'', 2010<ref name="Huuse 2010">Huuse, M, Jackson, C A-J, Van Rensbergen, P, Davies, R J, Flemings, P B, and Dixon, R J. (2010). Subsurface sediment remobilization and fluid flow in sedimentary basins: an overview. ''Basin Research'', '''22''', pp.342–360.</ref>). Their origin is uncertain, but may result from critical pressurisation of aquifers and hydrocarbon accumulations (Zühlsdorff & Spieß, 2004<ref name="Zühlsdorff 2004">Zühlsdorff, L, and Spieß, V. (2004). Three-dimensional seismic characterization of a venting site reveals compelling indications of natural hydraulic fracturing. ''Geology'', '''32''', pp.101–104.</ref>; Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>; Davies & Clarke, 2010<ref name="Davies 2010">Davies, R J, and Clarke, A L. (2010). Storage rather than venting after gas hydrate dissociation. ''Geology'', '''38''', pp.963–966.</ref>). Chimney development may be followed by fluid driven erosion and collapse of the surrounding rock (Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>). The release and expansion of gas from solution during advective flow may also play a role in development (Brown, 1990<ref name="Brown 1990">Brown, K M. (1990). The nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems. ''Journal of Geophysical Research: Solid Earth'', '''''95''''', pp.8969–8982.</ref>; Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>). Chimneys are clearly identifiable in seismic data as vertical aligned discontinuities in otherwise continuous units (Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>; Løseth ''et al.'', 2011<ref name="Løseth 2011">Løseth, H, Wensaas, L, Arntsen, B, Hanken, N-M, Basire, C, and Graue, K. (2011). 1000 m long gas blow-out chimneys. ''Marine and Petroleum Geology'', '''28''', pp.1047–1060.</ref>). Davies ''et al. ''(2012)<ref name="Davies 2012"><del style="font-weight: bold; text-decoration: none;">Davies, R J, Mathias, S A, Moss, J, Hustoft, S, and Newport, L. (2012). Hydraulic fractures: How far can they go? ''Marine and petroleum geology'', '''37''', pp.1–6.</del></ref> examined 368 chimneys from offshore Mauritania and showed that the average height was 247 metres, with the tallest chimney being 507 metres. In offshore Namibia 366 chimneys showed an average height of 360 metres, with the tallest being approximately 1,100 metres. In offshore Norway 466 chimneys showed an average height of 338 metres, with a maximum of 880 metres. From comparing natural with induced hydraulic fractures, Davies ''et al. ''(2012)<ref name="Davies 2012"></ref> conclude that the probability of an induced hydraulic fracture extending vertically more than 350 metres is about 1%. It should be noted that their conclusion is based on fracture height statistics alone and the mechanistic basis for fracture height control is not taken into account.</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The tallest example of natural hydraulic fracture result when they cluster and form chimneys (also termed pipes or blowout pipes). These have been observed to extend vertically for hundreds of metres (e.g. Cartwright ''et al.'', 2007<ref name="Cartwright 2007">Cartwright, J, Huuse, M, and Aplin, A. (2007). Seal bypass systems. ''American Association of Petroleum Geologists Bulletin'', 91, pp.1141–1166.</ref>; Huuse ''et al.'', 2010<ref name="Huuse 2010">Huuse, M, Jackson, C A-J, Van Rensbergen, P, Davies, R J, Flemings, P B, and Dixon, R J. (2010). Subsurface sediment remobilization and fluid flow in sedimentary basins: an overview. ''Basin Research'', '''22''', pp.342–360.</ref>). Their origin is uncertain, but may result from critical pressurisation of aquifers and hydrocarbon accumulations (Zühlsdorff & Spieß, 2004<ref name="Zühlsdorff 2004">Zühlsdorff, L, and Spieß, V. (2004). Three-dimensional seismic characterization of a venting site reveals compelling indications of natural hydraulic fracturing. ''Geology'', '''32''', pp.101–104.</ref>; Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>; Davies & Clarke, 2010<ref name="Davies 2010">Davies, R J, and Clarke, A L. (2010). Storage rather than venting after gas hydrate dissociation. ''Geology'', '''38''', pp.963–966.</ref>). Chimney development may be followed by fluid driven erosion and collapse of the surrounding rock (Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>). The release and expansion of gas from solution during advective flow may also play a role in development (Brown, 1990<ref name="Brown 1990">Brown, K M. (1990). The nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems. ''Journal of Geophysical Research: Solid Earth'', '''''95''''', pp.8969–8982.</ref>; Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>). Chimneys are clearly identifiable in seismic data as vertical aligned discontinuities in otherwise continuous units (Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>; Løseth ''et al.'', 2011<ref name="Løseth 2011">Løseth, H, Wensaas, L, Arntsen, B, Hanken, N-M, Basire, C, and Graue, K. (2011). 1000 m long gas blow-out chimneys. ''Marine and Petroleum Geology'', '''28''', pp.1047–1060.</ref>). Davies ''et al. ''(2012)<ref name="Davies 2012"></ref> examined 368 chimneys from offshore Mauritania and showed that the average height was 247 metres, with the tallest chimney being 507 metres. In offshore Namibia 366 chimneys showed an average height of 360 metres, with the tallest being approximately 1,100 metres. In offshore Norway 466 chimneys showed an average height of 338 metres, with a maximum of 880 metres. From comparing natural with induced hydraulic fractures, Davies ''et al. ''(2012)<ref name="Davies 2012"></ref> conclude that the probability of an induced hydraulic fracture extending vertically more than 350 metres is about 1%. It should be noted that their conclusion is based on fracture height statistics alone and the mechanistic basis for fracture height control is not taken into account.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Hydraulic fracture stimulation from a horizontal borehole is usually carried out in multiple stages with known volumes and compositions of fluid (e.g. Bell & Brannon, 2011<ref name="Bell 2011">Bell, C E, and Brannon, H D. (2011). Redesigning fracturing fluids for improving reliability and well performance in horizontal tight gas shale applications. In ''SPE Hydraulic Fracturing Technology Conference''. Society of Petroleum Engineers.</ref>). Rather than chimney formation, clustering of fractures commonly occurs along planes, which are theoretically orthogonal to the least principle stress direction. Therefore fundamental differences exist in the geometry of these fracture systems compared to those that cluster to form chimneys, the reasons for which are not yet understood (Davies ''et al.'', 2012<ref name="Davies 2012"></ref>).</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Hydraulic fracture stimulation from a horizontal borehole is usually carried out in multiple stages with known volumes and compositions of fluid (e.g. Bell & Brannon, 2011<ref name="Bell 2011">Bell, C E, and Brannon, H D. (2011). Redesigning fracturing fluids for improving reliability and well performance in horizontal tight gas shale applications. In ''SPE Hydraulic Fracturing Technology Conference''. Society of Petroleum Engineers.</ref>). Rather than chimney formation, clustering of fractures commonly occurs along planes, which are theoretically orthogonal to the least principle stress direction. Therefore fundamental differences exist in the geometry of these fracture systems compared to those that cluster to form chimneys, the reasons for which are not yet understood (Davies ''et al.'', 2012<ref name="Davies 2012"></ref>).</div></td></tr>
</table>Ajhilhttp://earthwise-staging.bgs.ac.uk/index.php?title=OR/15/066_Fracture_propagation&diff=44311&oldid=prevAjhil: /* Observations of natural hydraulic fracturing */2019-12-03T12:39:13Z<p><span dir="auto"><span class="autocomment">Observations of natural hydraulic fracturing</span></span></p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 13:39, 3 December 2019</td>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==Observations of natural hydraulic fracturing== </div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>==Observations of natural hydraulic fracturing== </div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Richard Davies and co-workers (Davies ''et al.'', 2012<ref name="Davies 2012">Davies, R J, Mathias, S A, Moss, J, Hustoft, S, and Newport, L. (2012). Hydraulic fractures: How far can they go? ''Marine and petroleum geology'', '''37''', pp.1–6.</ref>) published a study on natural hydraulic fractures, which is useful in assessing the geometric extent of induced or stimulated hydraulic fracturing.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Richard Davies and co-workers (Davies ''et al.'', 2012<ref name="Davies 2012">Davies, R J, Mathias, S A, Moss, J, Hustoft, S, and Newport, L. (2012). Hydraulic fractures: How far can they go? ''Marine and petroleum geology'', '''37''', pp.1–6.</ref>) published a study on natural hydraulic fractures, which is useful in assessing the geometric extent of induced or stimulated hydraulic fracturing.</div></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Cosgrove (1995)<ref name="Cosgrove 1995">Cosgrove, J W. (1995). The expression of hydraulic fracturing in rocks and sediments. In: ''Fractography: Fracture Topography as a Tool in Fracture Mechanics and Stress Analysis''. Geological Society Special Publication No.'''92''', pp.187–196.</ref> showed that natural hydraulic fractures can be observed in outcrops from the centimetre to metre scale. There are several types of natural hydraulic fracture that have all been extensively studied, including: injectities (e.g. Hurst ''et al.'', 2011<ref name="Hurst 2011">Hurst, A, Scott, A, and Vigorito, M. (2011). Physical characteristics of sand injectites. ''Earth Science Reviews'', 106, pp.215–246.</ref>), igneous dykes (e.g. Polteau ''et al.'', 2008<ref name="Polteau 2008">Polteau, S, Mazzini, A, Galland, O, Planke, S, and Malthe-Sørenssen, A. (2008). Saucershaped intrusions: occurrences, emplacement and implications. ''Earth and Planetary Science Letters'', '''266''', pp.195–204.</ref>), veins (e.g. Cosgrove, 1995<ref name="Cosgrove 1995"></ref>), coal cleats (e.g. Laubach ''et al.'', 1998<ref name="Laubach 1998">Laubach, S E, Marrett, R A, Olson, J E, and Scott, A R. (1998). Characteristics and origins of coal cleat: a review. ''International Journal of Coal Geology'', 35, pp.175–207.</ref>), and joints (e.g. McConaughy & Engelder, 1999<ref name="McConaughy 1999">McConaughy, D T, and Engelder, T. (1999). Joint interaction with embedded concretions: joint loading configurations inferred from propagation paths. ''Journal of Structural Geology'', 21, pp.1637–1652.</ref>). Savalli & Engelder (2005)<ref name="Savalli 2005"><del style="font-weight: bold; text-decoration: none;">Savalli, L, and Engelder, T. (2005). Mechanisms controlling rupture shape during subcritical growth of joints in layered rock. ''Geological Society of America Bulletin'', 117, pp.436–449.</del></ref> showed that growth of natural hydraulic fractures could be studied in the Devonian Marcellus formation in the US on the basis of plume lines that occur over a range of scales from centimetre to metre scale. The formation of these natural features is inferred to derive from gas diffusion and expansion within the shale during multiple propagation events.</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Cosgrove (1995)<ref name="Cosgrove 1995">Cosgrove, J W. (1995). The expression of hydraulic fracturing in rocks and sediments. In: ''Fractography: Fracture Topography as a Tool in Fracture Mechanics and Stress Analysis''. Geological Society Special Publication No.'''92''', pp.187–196.</ref> showed that natural hydraulic fractures can be observed in outcrops from the centimetre to metre scale. There are several types of natural hydraulic fracture that have all been extensively studied, including: injectities (e.g. Hurst ''et al.'', 2011<ref name="Hurst 2011">Hurst, A, Scott, A, and Vigorito, M. (2011). Physical characteristics of sand injectites. ''Earth Science Reviews'', 106, pp.215–246.</ref>), igneous dykes (e.g. Polteau ''et al.'', 2008<ref name="Polteau 2008">Polteau, S, Mazzini, A, Galland, O, Planke, S, and Malthe-Sørenssen, A. (2008). Saucershaped intrusions: occurrences, emplacement and implications. ''Earth and Planetary Science Letters'', '''266''', pp.195–204.</ref>), veins (e.g. Cosgrove, 1995<ref name="Cosgrove 1995"></ref>), coal cleats (e.g. Laubach ''et al.'', 1998<ref name="Laubach 1998">Laubach, S E, Marrett, R A, Olson, J E, and Scott, A R. (1998). Characteristics and origins of coal cleat: a review. ''International Journal of Coal Geology'', 35, pp.175–207.</ref>), and joints (e.g. McConaughy & Engelder, 1999<ref name="McConaughy 1999">McConaughy, D T, and Engelder, T. (1999). Joint interaction with embedded concretions: joint loading configurations inferred from propagation paths. ''Journal of Structural Geology'', 21, pp.1637–1652.</ref>). Savalli & Engelder (2005)<ref name="Savalli 2005"></ref> showed that growth of natural hydraulic fractures could be studied in the Devonian Marcellus formation in the US on the basis of plume lines that occur over a range of scales from centimetre to metre scale. The formation of these natural features is inferred to derive from gas diffusion and expansion within the shale during multiple propagation events.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The tallest example of natural hydraulic fracture result when they cluster and form chimneys (also termed pipes or blowout pipes). These have been observed to extend vertically for hundreds of metres (e.g. Cartwright ''et al.'', 2007<ref name="Cartwright 2007">Cartwright, J, Huuse, M, and Aplin, A. (2007). Seal bypass systems. ''American Association of Petroleum Geologists Bulletin'', 91, pp.1141–1166.</ref>; Huuse ''et al.'', 2010<ref name="Huuse 2010">Huuse, M, Jackson, C A-J, Van Rensbergen, P, Davies, R J, Flemings, P B, and Dixon, R J. (2010). Subsurface sediment remobilization and fluid flow in sedimentary basins: an overview. ''Basin Research'', '''22''', pp.342–360.</ref>). Their origin is uncertain, but may result from critical pressurisation of aquifers and hydrocarbon accumulations (Zühlsdorff & Spieß, 2004<ref name="Zühlsdorff 2004">Zühlsdorff, L, and Spieß, V. (2004). Three-dimensional seismic characterization of a venting site reveals compelling indications of natural hydraulic fracturing. ''Geology'', '''32''', pp.101–104.</ref>; Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>; Davies & Clarke, 2010<ref name="Davies 2010">Davies, R J, and Clarke, A L. (2010). Storage rather than venting after gas hydrate dissociation. ''Geology'', '''38''', pp.963–966.</ref>). Chimney development may be followed by fluid driven erosion and collapse of the surrounding rock (Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>). The release and expansion of gas from solution during advective flow may also play a role in development (Brown, 1990<ref name="Brown 1990">Brown, K M. (1990). The nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems. ''Journal of Geophysical Research: Solid Earth'', '''''95''''', pp.8969–8982.</ref>; Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>). Chimneys are clearly identifiable in seismic data as vertical aligned discontinuities in otherwise continuous units (Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>; Løseth ''et al.'', 2011<ref name="Løseth 2011">Løseth, H, Wensaas, L, Arntsen, B, Hanken, N-M, Basire, C, and Graue, K. (2011). 1000 m long gas blow-out chimneys. ''Marine and Petroleum Geology'', '''28''', pp.1047–1060.</ref>). Davies ''et al. ''(2012)<ref name="Davies 2012">Davies, R J, Mathias, S A, Moss, J, Hustoft, S, and Newport, L. (2012). Hydraulic fractures: How far can they go? ''Marine and petroleum geology'', '''37''', pp.1–6.</ref> examined 368 chimneys from offshore Mauritania and showed that the average height was 247 metres, with the tallest chimney being 507 metres. In offshore Namibia 366 chimneys showed an average height of 360 metres, with the tallest being approximately 1,100 metres. In offshore Norway 466 chimneys showed an average height of 338 metres, with a maximum of 880 metres. From comparing natural with induced hydraulic fractures, Davies ''et al. ''(2012)<ref name="Davies 2012"></ref> conclude that the probability of an induced hydraulic fracture extending vertically more than 350 metres is about 1%. It should be noted that their conclusion is based on fracture height statistics alone and the mechanistic basis for fracture height control is not taken into account.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>The tallest example of natural hydraulic fracture result when they cluster and form chimneys (also termed pipes or blowout pipes). These have been observed to extend vertically for hundreds of metres (e.g. Cartwright ''et al.'', 2007<ref name="Cartwright 2007">Cartwright, J, Huuse, M, and Aplin, A. (2007). Seal bypass systems. ''American Association of Petroleum Geologists Bulletin'', 91, pp.1141–1166.</ref>; Huuse ''et al.'', 2010<ref name="Huuse 2010">Huuse, M, Jackson, C A-J, Van Rensbergen, P, Davies, R J, Flemings, P B, and Dixon, R J. (2010). Subsurface sediment remobilization and fluid flow in sedimentary basins: an overview. ''Basin Research'', '''22''', pp.342–360.</ref>). Their origin is uncertain, but may result from critical pressurisation of aquifers and hydrocarbon accumulations (Zühlsdorff & Spieß, 2004<ref name="Zühlsdorff 2004">Zühlsdorff, L, and Spieß, V. (2004). Three-dimensional seismic characterization of a venting site reveals compelling indications of natural hydraulic fracturing. ''Geology'', '''32''', pp.101–104.</ref>; Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>; Davies & Clarke, 2010<ref name="Davies 2010">Davies, R J, and Clarke, A L. (2010). Storage rather than venting after gas hydrate dissociation. ''Geology'', '''38''', pp.963–966.</ref>). Chimney development may be followed by fluid driven erosion and collapse of the surrounding rock (Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>). The release and expansion of gas from solution during advective flow may also play a role in development (Brown, 1990<ref name="Brown 1990">Brown, K M. (1990). The nature and hydrogeologic significance of mud diapirs and diatremes for accretionary systems. ''Journal of Geophysical Research: Solid Earth'', '''''95''''', pp.8969–8982.</ref>; Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>). Chimneys are clearly identifiable in seismic data as vertical aligned discontinuities in otherwise continuous units (Cartwright ''et al.'', 2007<ref name="Cartwright 2007"></ref>; Løseth ''et al.'', 2011<ref name="Løseth 2011">Løseth, H, Wensaas, L, Arntsen, B, Hanken, N-M, Basire, C, and Graue, K. (2011). 1000 m long gas blow-out chimneys. ''Marine and Petroleum Geology'', '''28''', pp.1047–1060.</ref>). Davies ''et al. ''(2012)<ref name="Davies 2012">Davies, R J, Mathias, S A, Moss, J, Hustoft, S, and Newport, L. (2012). Hydraulic fractures: How far can they go? ''Marine and petroleum geology'', '''37''', pp.1–6.</ref> examined 368 chimneys from offshore Mauritania and showed that the average height was 247 metres, with the tallest chimney being 507 metres. In offshore Namibia 366 chimneys showed an average height of 360 metres, with the tallest being approximately 1,100 metres. In offshore Norway 466 chimneys showed an average height of 338 metres, with a maximum of 880 metres. From comparing natural with induced hydraulic fractures, Davies ''et al. ''(2012)<ref name="Davies 2012"></ref> conclude that the probability of an induced hydraulic fracture extending vertically more than 350 metres is about 1%. It should be noted that their conclusion is based on fracture height statistics alone and the mechanistic basis for fracture height control is not taken into account.</div></td></tr>
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