Subsurface fluid flow in the deep‐water Kwanza Basin, offshore Angola

Serié, Christophe; Huuse, Mads; Schødt, Niels H.; Brooks, James M.; Williams, Alan

doi:10.1111/bre.12169

Cited by 46 publications

(47 citation statements)

References 80 publications

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“…This type of seepage was called Active seepage [10]. Other basins with similar active seepage include offshore Nigeria [27]; offshore South Caspian Basin [28]; offshore Angola [29]; and Black Sea [30,31]. In areas of active seepage, hydrocarbon movement to the near-surface is not always continuous, but can be episodic [32][33][34][35][36].…”

Section: Seepage Activity: Active Versus Passivementioning

confidence: 99%

Evaluation of Near-Surface Gases in Marine Sediments to Assess Subsurface Petroleum Gas Generation and Entrapment

Abrams

2017

Geosciences

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Gases contained within near-surface marine sediments can be derived from multiple sources: shallow microbial activity, thermal cracking of organic matter and inorganic materials, or magmatic-mantle degassing. Each origin will display a distinctive hydrocarbon and non-hydrocarbon composition as well as compound-specific isotope signature and thus the interpretation of origin should be relatively straightforward. Unfortunately, this is not always the case due to in situ microbial alteration, non-equilibrium phase partitioning, mixing, and fractionation related to the gas extraction method. Sediment gases can reside in the interstitial spaces, bound to mineral or organic surfaces and/or entrapped in carbonate inclusions. The interstitial sediment gases are contained within the sediment pore space, either dissolved in the pore waters (solute) or as free (vapour) gas. The bound gases are believed to be attached to organic and/or mineral surfaces, entrapped in structured water or entrapped in authigenic carbonate inclusions. The purpose of this paper is to provide a review of the gas types found within shallow marine sediments and examine issues related to gas sampling and extraction. In addition, the paper will discuss how to recognise mixing, alteration and fractionation issues to best interpret the seabed geochemical results and determine gas origin to assess subsurface petroleum gas generation and entrapment.

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Section: Seepage Activity: Active Versus Passivementioning

confidence: 99%

Evaluation of Near-Surface Gases in Marine Sediments to Assess Subsurface Petroleum Gas Generation and Entrapment

Abrams

2017

Geosciences

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“…These gases are commonly thermogenic in origin and are sourced by relatively deep leaking reservoirs. Natural gas hydrate systems associated with thermogenic hydrocarbons have been observed in many different sedimentary basins worldwide [Diaconescu et al, 2001;Sassen et al, 2001aSassen et al, , 2001bSassen et al, , 2001cMazurenko et al, 2002;Blinova et al, 2003;Kida et al, 2006;Lu et al, 2007;Bourry et al, 2009;Pape et al, 2010Pape et al, , 2014Ruffine et al, 2013;Smith et al, 2014;Serié et al, 2016]. However, S II and S H gas hydrates have often been directly sampled only at or close to the seafloor, without a complete penetration and direct sampling throughout the gas hydrate stability zone (GHSZ) [Sassen et al, 2001a[Sassen et al, , 2001b[Sassen et al, , 2001cPohlman et al, 2005;Lu et al, 2007;Bourry et al, 2009;Klapp et al, 2010].…”

Section: Introductionmentioning

confidence: 99%

Structure II gas hydrates found below the bottom‐simulating reflector

Paganoni

Cartwright

Foschi

et al. 2016

Geophysical Research Letters

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Gas hydrates are a major component in the organic carbon cycle. Their stability is controlled by temperature, pressure, water chemistry, and gas composition. The bottom‐simulating reflector (BSR) is the primary seismic indicator of the base of hydrate stability in continental margins. Here we use seismic, well log, and core data from the convergent margin offshore NW Borneo to demonstrate that the BSR does not always represent the base of hydrate stability and can instead approximate the boundary between structure I hydrates above and structure II hydrates below. At this location, gas hydrate saturation below the BSR is higher than above and a process of chemical fractionation of the migrating free gas is responsible for the structure I‐II transition. This research shows that in geological settings dominated by thermogenic gas migration, the hydrate stability zone may extend much deeper than suggested by the BSR.

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“…Especially the Lower Congo Basin (LCB) has been investigated extensively with respect to the fluid flow systems in its upper and middle slope setting (Andresen & Huuse, ; Andresen et al, ; Gay et al, , ; Gay, Lopez, Cochonat, et al, ; Gay et al, ; Ho et al, ; Lucazeau et al, ; Maia et al, ; Serié et al, ). The lower slope and the salt front, however, received less attention although hosting abundant fluid flow phenomena (Olu et al, ; Ondréas et al, ; Sahling et al, ; Wenau et al, , ).…”

Section: Geological Settingmentioning

confidence: 99%

“…In recent years, most attention has been paid to seepage processes within hydrocarbon basins that typically contain thick sedimentary sequences and the potential for hydrocarbon trapping. Research focused on the geological setting of fluid migration pathways (Andresen et al, ; Cartwright et al, ; Serié et al, ) and the formation of seafloor seepage features in particular (Cathles et al, ; Ho et al, ; Sultan et al, , ). In association with hydrocarbon migration, the interaction of sand injectites with fluid flow systems has been investigated specifically (Cartwright et al, ; Hurst et al, ; Monnier et al, ; Shoulders & Cartwright, ).…”

Section: Introductionmentioning

confidence: 99%

Active Seafloor Seepage Along Hydraulic Fractures Connected to Lateral Stress From Salt‐Related Rafting: Regab Pockmark, Congo Fan

Wenau

Spieß

2018

JGR Solid Earth

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Seafloor seepage is a widespread phenomenon within salt‐influenced basins as the deformation provides pathways for hydrocarbons to reach the seafloor. However, only minor attention has been given to the distal parts of such systems where the impact of salt tectonic deformation is relatively unpronounced. The stress put on the sedimentary column by moving salt on a continental margin may influence fluid flow systems even outside of the salt province. This stress may lead to overpressure formation within reservoirs and determine the orientation of overpressure‐induced fractures. Seepage in the Congo Fan has been discovered in such a distal position at the Regab pockmark, about 35 km west of the salt front, and its geology and biology have been studied extensively in recent years. We present high‐resolution multichannel seismic data from the Regab pockmark that reveal the underlying migration pathways from a buried channel flank 300 m below seafloor to the seafloor via hydraulic fractures in the sealing overburden. Local doming of the reservoir and the remobilization and uplift of sedimentary strata along the migration pathways are interpreted as the result of overpressure within the reservoir. The orientation of the hydraulic fractures is WSW‐ENE, and the fracture outline corresponds to the area of most intense seepage activity within the seafloor pockmark. Along with a similar orientation of other fractures in the vicinity, we propose that this alignment is due to the stress imposed on the sedimentary column in the fan by the seaward moving salt and rafting sedimentary packages of the salt province further east.

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Subsurface fluid flow in the deep‐water Kwanza Basin, offshore Angola

Cited by 46 publications

References 80 publications

Evaluation of Near-Surface Gases in Marine Sediments to Assess Subsurface Petroleum Gas Generation and Entrapment

Evaluation of Near-Surface Gases in Marine Sediments to Assess Subsurface Petroleum Gas Generation and Entrapment

Structure II gas hydrates found below the bottom‐simulating reflector

Active Seafloor Seepage Along Hydraulic Fractures Connected to Lateral Stress From Salt‐Related Rafting: Regab Pockmark, Congo Fan

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