Exhumation charge: The last gasp of a petroleum source rock and implications for unconventional shale resources

English, Joseph M.; English, Kara L.; Corcoran, D. V.; Toussaint, Fabrice

doi:10.1306/07271514224

Cited by 34 publications

(5 citation statements)

References 42 publications

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“…Approximately 19.0 % -28.5 % of the initial total gas content was lost in the process of intensive tectonic uplifts and denudation, and overpressure caused by thermocatalytic gas generation was continuously released until the present-day overpressure state. Our results are in good agreement with the "Exhumation Charge" model demonstrated by English et al (2016). English et al (2016) found that if the source rock is exhumed to shallower depths after peak burial, pore pressure reduction and the associated volumetric expansion of the petroleum-particularly of the gaseous-phase in the pore system will result in the discharge of additional petroleum into the adjacent carrier bed or reservoir formations.…”

Section: Closed Fluid Model For Overpressure Evolution and Implication For Shale Gas Accumulationsupporting

confidence: 89%

“…Our results are in good agreement with the "Exhumation Charge" model demonstrated by English et al (2016). English et al (2016) found that if the source rock is exhumed to shallower depths after peak burial, pore pressure reduction and the associated volumetric expansion of the petroleum-particularly of the gaseous-phase in the pore system will result in the discharge of additional petroleum into the adjacent carrier bed or reservoir formations.…”

Section: Closed Fluid Model For Overpressure Evolution and Implication For Shale Gas Accumulationsupporting

confidence: 89%

“…significantly with burial depth (English et al, 2016). Consequently, the storage or retention capacity of the over-maturity O 3 w-S 1 l shales will become dominated by free gas component (Ross and Bustin, 2008;, i.e., the magnitude of gas generation overpressure in the O 3 w-S 1 l shales is determined by the total gas contents, especially the free gas contents.…”

Section: Closed Fluid Model For Overpressure Evolution and Implication For Shale Gas Accumulationmentioning

confidence: 99%

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Overpressure generation and evolution in Lower Paleozoic gas shales of the Jiaoshiba region, China: Implications for shale gas accumulation

Gao

Zhang

et al. 2019

Marine and Petroleum Geology

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Section: Closed Fluid Model For Overpressure Evolution and Implication For Shale Gas Accumulationsupporting

confidence: 89%

Section: Closed Fluid Model For Overpressure Evolution and Implication For Shale Gas Accumulationsupporting

confidence: 89%

Section: Closed Fluid Model For Overpressure Evolution and Implication For Shale Gas Accumulationmentioning

confidence: 99%

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Overpressure generation and evolution in Lower Paleozoic gas shales of the Jiaoshiba region, China: Implications for shale gas accumulation

Gao

Zhang

et al. 2019

Marine and Petroleum Geology

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“…This is the case, for instance, of pre‐Permian rocks underneath the Hercynian unconformity in North Africa (e.g. English et al ., ) and Mesozoic rocks underlying the Base Tertiary Unconformity in the North Sea. A comprehension of the full, multiphase structural evolution of these rocks is needed to provide meaningful predictions, for instance, of their fracture pattern.…”

Section: Discussionmentioning

confidence: 99%

Fracturing and fluid‐flow during post‐rift subsidence in carbonates of the Jandaíra Formation, Potiguar Basin, NE Brazil

Bertotti

Graaf²,

Bisdom

et al. 2017

Basin Research

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Pervasive fracture networks are common in many reservoir-scale carbonate bodies even in the absence of large deformation and exert a major impact on their mechanical and flow behaviour. The Upper Cretaceous Janda ıra Formation is a few hundred meters thick succession of shallow water carbonates deposited during the early post-rift stage of the Potiguar rift (NE Brazil). The Janda ıra Formation in the present onshore domain experienced <1.5 km thermal subsidence and, following Tertiary exhumation, forms outcrops over an area of >1000 km 2 . The carbonates have a gentle, <5⁰, dip to the NE and are affected by few regional, low displacement faults or folds. Despite their simple tectonic history, carbonates display ubiquitous open fractures, sub-vertical veins, and sub-vertical as well as sub-horizontal stylolites. Combining structural analysis, drone imaging, isotope studies and mathematical modelling, we reconstruct the fracturing history of the Janda ıra Formation during and following subsidence and analyse the impact fractures had on coeval fluid flow. We find that Janda ıra carbonates, fully cemented after early diagenesis, experienced negligible deformation during the first few hundreds of meters of subsidence but were pervasively fractured when they reached depths >400-500 m. Deformation was accommodated by a dense network of sub-vertical mode I and hybrid fractures associated with sub-vertical stylolites developed in a stress field characterised by a sub-horizontal r 1 and sub-vertical r 2 . The development of a network of hybrid fractures, rarely reported in the literature, activated the circulation of waters charged in the mountainous region, flowing along the porous Ac ßu sandstone underlying the Janda ıra carbonates and rising to the surface through the fractured carbonates. With persisting subsidence, carbonates reached depths of 800-900 m entering a depth interval characterised by a sub-vertical r 1 . At this stage, sub-horizontal stylolites developed liberating calcite which sealed the sub-vertical open fractures transforming them in veins and preventing further flow. During Tertiary exhumation, several of the pre-existing veins and stylolites opened and became longer, and new fractures were created typically with the same directions of the older features. The simplicity of our model suggests that most rocks in passive margin settings might have followed a similar evolution and thus display similar structures.

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“…Unless the exhumed basin is situated along a migration route from an adjacent normally subsiding basin that is actively generating hydrocarbons, post-exhumation charging of petroleum traps can only occur via the redistribution of hydrocarbons already existing within the basin (e.g. Doré et al 2002 or via late-stage exhumation charge during final depressurization of the source rock (English et al 2016a). Aside from these potential post-exhumation charge or remigration mechanisms, the petroleum prospectivity of an exhumed basin is largely dependent on the ability of pre-existing traps to retain oil and gas volumes during and after the exhumation event.…”

mentioning

confidence: 99%

State of stress in exhumed basins and implications for fluid flow: insights from the Illizi Basin, Algeria

English¹,

Finkbeiner

English³

et al. 2017

Self Cite

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The petroleum prospectivity of an exhumed basin is largely dependent on the ability of preexisting traps to retain oil and gas volumes during and after the exhumation event. Although faults may act as lateral seals in petroleum traps, they may start to become hydraulically conductive again and enable fluid flow and hydrocarbon leakage during fault reactivation. Herein, we constrain the present-day in situ stresses of the exhumed Illizi Basin in Algeria, and demonstrate that the primary N-S and NW-SE (vertical strike-slip) fault systems in the study area are close to critical stress (i.e., incipient state of shear failure). In contrast, the overpressured and unexhumed Berkine Basin and Hassi Messaoud areas to the north do not appear to be characterized by critical stress conditions. We present conceptual models of stress evolution and demonstrate that a sedimentary basin with benign in situ stresses at maximum burial may change to being characterized by critical stress conditions on existing fault systems during exhumation. These models are supportive of the idea that breaching of a closed, overpressured system during exhumation of the Illizi Basin may have been a driving mechanism for regional updip flow of high-salinity formation water within the Ordovician reservoirs during Eocene-Miocene time. This work also has implications for petroleum exploration in exhumed basins. Fault-bounded traps with faults oriented at a high-angle to the maximum principal horizontal stress direction in strike-slip or normal-faulting stress regimes are more likely to have retained hydrocarbons in exhumed basins in comparison to fault-bounded traps with faults that are more optimally oriented for shear failure and, therefore, have a greater propensity to become critically stressed during exhumation.

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Exhumation charge: The last gasp of a petroleum source rock and implications for unconventional shale resources

Cited by 34 publications

References 42 publications

Overpressure generation and evolution in Lower Paleozoic gas shales of the Jiaoshiba region, China: Implications for shale gas accumulation

Overpressure generation and evolution in Lower Paleozoic gas shales of the Jiaoshiba region, China: Implications for shale gas accumulation

Fracturing and fluid‐flow during post‐rift subsidence in carbonates of the Jandaíra Formation, Potiguar Basin, NE Brazil

State of stress in exhumed basins and implications for fluid flow: insights from the Illizi Basin, Algeria

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