Vertical anomaly clusters: Evidence for vertical gas migration across multilayered sealing sequences

Foschi, Martino; Cartwright, Joseph Albert; Peel, Frank

doi:10.1306/04051413121

Cited by 17 publications

(23 citation statements)

References 55 publications

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“…The presence of a migrating gas within the chimney is strongly suggested by the common effects of attenuation and velocity push‐downs (O'Doherty & Anstey, ; Kuster & Toksoz, ; Bała, ; Pietsch & Strzetelski, , ; Kobylarski et al ., ; Pietsch et al ., ; Foschi et al ., ), amplitude dimming (Løseth et al ., ; Boait et al ., ). High‐amplitude rims to the chimney may reflect gas‐charged zones within the surrounding fine‐grained host (Heggland, ; Arntsen et al ., ; Løseth et al ., ).…”

Section: Resultsmentioning

confidence: 99%

Interpretation of a gas chimney in the Polish Carpathian Foredeep based on integrated seismic and geochemical data

et al. 2016

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Gas chimneys are common in offshore petroliferous basins, but little known on land where seismic columnar anomalies are often attributed as poor data quality or processing artefacts. This study utilizes high-quality 3D seismic data to document a seismic columnar anomaly penetrating through the Miocene heterolithic submarine fan-deltaic infill of the Carpathian Foredeep. The interpreted gas chimney exhibits vertically clustered velocity push-down features throughout the attenuated amplitude column accompanied by gas shows in well tests, has its root in gas-bearing Palaeozoic interval and culminates in an anomalous geochemical gas record at soil level. The chimney system, ca 2 km in height and 500-m wide, begins above the flank of a rotational bedrock fault-block and extends vertically along a fault-controlled conduit. At shallower levels, it passes upwards into amplitude wipeout zones that spread laterally around and partly across thin, gas-charged reservoirs showing bright spots associated with an AVO response. At shallow levels, gas pathways through muddy slope and deltaic clinoforms are not imaged in low-fold regions of the seismic volume. The surface geochemical anomalies, in contrast to the microbial methane signature of the Miocene succession, show significant enrichment in higher alkanes and alkenes with C 2 H 6 /C 3 H 8 ratios indicative of a deep-sourced, thermogenic gas or gas condensate. These anomalies form a semi-enclosed halo around the chimney. Despite the juxtaposition of biogenic and thermogenic methane, the chimney structure imaged on seismic data supports a causal link of gases derived from Palaeozoic source rocks ascending to the surface.

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Section: Resultsmentioning

confidence: 99%

Interpretation of a gas chimney in the Polish Carpathian Foredeep based on integrated seismic and geochemical data

et al. 2016

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“…Our findings suggest that the dominant mechanisms responsible for the spontaneous formation of fluid escape pipes in the subsurface are viscous creep of the porous matrix, decompaction weakening, and hydro-mechanical coupling. Numerical simulations predict that the activated creep leads to the rapid formation of chimneys in low-viscosity shales, expected to be natural flow barriers 13 , 21 . Thus, resolving the variations in flow patterns, viscous compaction and associated stresses is vital to evaluate storage potential and geological barrier integrity in oil and gas operations 13 , 44 and waste sequestration 38 .…”

Section: Discussionmentioning

confidence: 99%

“…These focussed flow pathways provide an important and efficient transport mechanism for fluid migration, yet the physical controls on their formation are not well understood and still debated 18 – 20 . We propose hydro-mechanical coupling as the dominant underlying physical process for the formation of high-permeability pathways, based on the following observations: (1) Vertical chimneys occur in various sedimentary basin lithologies 12 , 14 , 21 and appear unaffected by rock composition, refuting chemical reactions as the main formation mechanism. (2) The vertical chimneys develop through existing formations and are not influenced by sedimentary layering or structural features such as faults 13 , 21 , 22 .…”

Section: Introductionmentioning

confidence: 99%

“…We propose hydro-mechanical coupling as the dominant underlying physical process for the formation of high-permeability pathways, based on the following observations: (1) Vertical chimneys occur in various sedimentary basin lithologies 12 , 14 , 21 and appear unaffected by rock composition, refuting chemical reactions as the main formation mechanism. (2) The vertical chimneys develop through existing formations and are not influenced by sedimentary layering or structural features such as faults 13 , 21 , 22 . These observations also suggest that they mainly do not form by reactivation of pre-existing structures, but are the outcome of a self-sustaining dynamic process independent of the inherited geological setting.…”

Section: Introductionmentioning

confidence: 99%

“…The clay content of sediments strongly enhances creep and self-sealing capabilities while hindering the propagation of brittle fractures 37 . Thus, ‘soft’ clay-rich rocks are regarded as natural barriers 21 , 37 , 38 and are recommended as caprock for storage operations. However, although brittle processes are inhibited, a time-dependent creep rheology may lead to localised flow of the sedimentary material in response to applied stress, proportional to bulk viscosity values in the range of 10 16 –10 13 Pa.s 37 , 39 .…”

Section: Introductionmentioning

confidence: 99%

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Spontaneous formation of fluid escape pipes from subsurface reservoirs

Räss

Simon²,

Podladchikov

2018

Sci Rep

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Ubiquitous observations of channelised fluid flow in the form of pipes or chimney-like features in sedimentary sequences provide strong evidence for significant transient permeability-generation in the subsurface. Understanding the mechanisms and dynamics for spontaneous flow localisation into fluid conductive chimneys is vital for natural fluid migration and anthropogenic fluid and gas operations, and in waste sequestration. Yet no model exists that can predict how, when, or where these conduits form. Here we propose a physical mechanism and show that pipes and chimneys can form spontaneously through hydro-mechanical coupling between fluid flow and solid deformation. By resolving both fluid flow and shear deformation of the matrix in three dimensions, we predict fluid flux and matrix stress distribution over time. The pipes constitute efficient fluid pathways with permeability enhancement exceeding three orders of magnitude. We find that in essentially impermeable shale (10−19 m2), vertical fluid migration rates in the high-permeability pipes or chimneys approach rates expected in permeable sandstones (10−15 m2). This previously unidentified fluid focusing mechanism bridges the gap between observations and established conceptual models for overcoming and destroying assumed impermeable barriers. This mechanism therefore has a profound impact on assessing the evolution of leakage pathways in natural gas emissions, for reliable risk assessment for long-term subsurface waste storage, or CO2 sequestration.

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Gas chimney and hydrocarbon detection using combined BBO and artificial neural network with hybrid seismic attributes

2019

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Vertical anomaly clusters: Evidence for vertical gas migration across multilayered sealing sequences

Cited by 17 publications

References 55 publications

Interpretation of a gas chimney in the Polish Carpathian Foredeep based on integrated seismic and geochemical data

Interpretation of a gas chimney in the Polish Carpathian Foredeep based on integrated seismic and geochemical data

Spontaneous formation of fluid escape pipes from subsurface reservoirs

Gas chimney and hydrocarbon detection using combined BBO and artificial neural network with hybrid seismic attributes

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