Sand remobilization and injection above an active salt diapir: the Tyr sand of the Nini Field, Eastern North Sea

AbstractMachar is one of several diapir fields located in the Eastern Trough of the UK Central North Sea. It contains light oil in fractured Cretaceous–Danian chalk and Paleocene sandstones draped over and around a tall, steeply-dipping salt diapir that had expressed seafloor relief during chalk deposition. The reservoir geology represents a complex interplay of sedimentology and evolving structure, with slope-related redeposition of both the chalk and sandstone reservoirs affecting distribution and reservoir quality. The best reservoir quality occurs in resedimented chalk (debris flows) and high-density turbidite sandstones. Mapping and characterizing the different facies present has been key to reservoir understanding.The field has been developed by water injection, with conventional sweep in the sandstones and imbibition drive in the chalk. Although the chalk has high matrix microporosity, permeability is typically less than 2 mD, and fractures are essential for achieving high flow rates; test permeabilities can be up to 1500 mD. The next phase of development is blowdown, where water injection is stopped and the field allowed to depressurize. This commenced in February 2018.

Download Full-text

Dissolution collapse of a growing diapir from radial, concentric, and salt-withdrawal faults overprinting in the Salinas de Oro salt diapir, northern Spain

Quaternary Research ◽

10.1017/qua.2016.17 ◽

2017 ◽

Vol 87 (2) ◽

pp. 331-346

Author(s):

Jesús Guerrero

Keyword(s):

Fracture Pattern ◽

Salt Diapir ◽

Normal Faults ◽

Northern Spain ◽

Concentric Ring ◽

Quaternary Deposits ◽

Ring Fracture ◽

Active Salt ◽

Roof Strata ◽

Salt Flow

AbstractA geomorphic investigation of the Salinas de Oro salt diapir in the Pyrenees reveals that the ring fracture pattern related to the karstic collapse of the diapir crest may vary significantly depending on the rates of dissolution and salt flow, and the rheology of the overburden. The salt diapir has well-developed concentric faults related to salt dissolution subsidence throughout the Quaternary. Roof strata accommodate subsidence by a combination of downward sagging and brittle collapse leading to the development of a ring monocline that is broken by 5 to 20 m throw conjugated normal faults and a 40 m throw, 9.5-km-long and 200-m-wide keystone graben. The salt diapir top has >100-m-long sinkholes that coalesce to form hollows >70 m deep. Up to 3-km-long radial grabens with a 70 to 90 m vertical throw overprint concentric-ring faulting and displace Quaternary deposits demonstrating active salt flow and diapir rise. Radial faults are linked with salt-withdrawal faults of the Andia Fault Zone (AFZ). Salt flow from the AFZ into the Salinas de Oro salt diapir causes brittle gravitational extension of limestone strata leading to a sequence of grabens and Quaternary faults >10 km long and several hundred meters deep.

Download Full-text

Discrete element modeling of the faulting in the sedimentary cover above an active salt diapir

Journal of Structural Geology ◽

10.1016/j.jsg.2008.10.007 ◽

2009 ◽

Vol 31 (9) ◽

pp. 989-995 ◽

Cited By ~ 14

Author(s):

Hongwei Yin ◽

Jie Zhang ◽

Lingsen Meng ◽

Yuping Liu ◽

Shijing Xu

Keyword(s):

Sedimentary Cover ◽

Discrete Element ◽

Salt Diapir ◽

Discrete Element Modeling ◽

Element Modeling ◽

Active Salt

Download Full-text

Methane emission and consumption at a North Sea gas seep (Tommeliten area)

Biogeosciences Discussions ◽

10.5194/bgd-2-1197-2005 ◽

2005 ◽

Vol 2 (4) ◽

pp. 1197-1241 ◽

Cited By ~ 12

Author(s):

H. Niemann ◽

M. Elvert ◽

M. Hovland ◽

B. Orcutt ◽

A. Judd ◽

...

Keyword(s):

North Sea ◽

Oil And Gas ◽

Salt Diapir ◽

Anaerobic Oxidation Of Methane ◽

Cold Seeps ◽

The North ◽

Oxidation Of Methane ◽

Phylogenetic Cluster ◽

Carbonate Formation ◽

Gas Seepage

Abstract. The North Sea hosts large coal, oil and gas reservoirs of commercial value. Natural leakage pathways of subsurface gas to the hydrosphere have been recognized during geological surveys (Hovland and Judd, 1988). The Tommeliten seepage area is part of the Greater Ekofisk area, which is situated above the Tommeliten Delta salt diapir in the central North Sea. In this study, we report of an active seep site (56°29.90'N, 2°59.80'E) located in the Tommeliten area, Norwegian Block 1/9, at 75 m water depth. Here, cracks in a buried marl horizon allow methane to migrate into overlying clay-silt and sandy sediments. Hydroacoustic sediment echosounding showed several venting spots coinciding with the apex of marl domes where methane is released into the water column and potentially to the atmosphere during deep mixing situations. In the vicinity of the gas seeps, sea floor observations showed small mats of giant sulphide-oxidizing bacteria above patches of black sediments and carbonate crusts, which are exposed 10 to 50 cm above seafloor forming small reefs. These Methane-Derived Authigenic Carbonates (MDACs) contain 13C-depleted, archaeal lipids indicating previous gas seepage and AOM activity. High amounts of sn2-hydroxyarchaeol relative to archaeol and low abundances of biphytanes in the crusts give evidence that ANaerobic MEthane-oxidising archaea (ANME) of the phylogenetic cluster ANME-2 were the potential mediators of Anaerobic Oxidation of Methane (AOM) at the time of carbonate formation. Small pieces of MDACs were also found subsurface at about 1.7 m sediment depth, associated with the Sulphate-Methane Transition Zone (SMTZ). The SMTZ of Tommeliten is characterized by elevated AOM and Sulphate Reduction (SR) rates, increased concentrations of 13C-depleted tetraether derived biphytanes, and specific bacterial Fatty Acids (FA). Further biomarker and 16S rDNA based analyses give evidence that AOM at the Tommeliten SMTZ is mediated by archaea belonging to the ANME-1b group and Sulphate Reducing Bacteria (SRB) most likely belonging to the Seep-SRB1 cluster. The zone of active methane consumption was restricted to a distinct horizon of about 20 cm. Concentrations of 13C-depleted lipid biomarkers (e.g. 500 ng g-dw-1 biphythanes, 140 ng g-dw-1 fatty acid ai-C15:0), cell numbers (1.5x108 cells cm-3), AOM and SR rates (3 nmol cm-3 d-1 in the SMTZ are 2-3 orders of magnitude lower compared to AOM zones of highly active cold seeps such as Hydrate Ridge or the Gulf of Mexico.

Download Full-text

The Mungo Field, Blocks 22/20a and 23/16a, UK North Sea

Geological Society London Memoirs ◽

10.1144/m52-2018-82 ◽

2020 ◽

Vol 52 (1) ◽

pp. 537-549 ◽

Cited By ~ 2

Author(s):

G. M. Baniak ◽

Z. Sayer ◽

H. Patterson ◽

R. Gooder ◽

N. Laing ◽

...

Keyword(s):

North Sea ◽

Water Injection ◽

Salt Diapir ◽

Submarine Fans ◽

Central Processing ◽

Economic Production ◽

Light Oil ◽

Early Paleocene ◽

The Uk ◽

Central North Sea

AbstractThe Mungo Field is a mature producing asset located in the UK Central North Sea. Discovered in 1989 and brought on production in 1998, it is the largest field within the Eastern Trough Area Project (ETAP). Production occurs via a normally unattended installation and is tied back to the ETAP Central Processing Facility. It is a pierced, four-way dip closure against a salt diapir. Light oil is present within steeply dipping Late Paleocene sandstone and Early Paleocene–Late Cretaceous chalk intervals. The vertical relief of the salt stock is around 1500 m TVDSS and top of the salt canopy lies at about 1350 m TVDSS.The Paleocene sandstones (Forties Sandstone Member of the Sele Formation, Lista Formation and Maureen Formation) make up the primary reservoir and have been extensively developed in three phases since 1998 under water injection and natural depletion. The sandstones were deposited as deep-water turbidite complexes (submarine fans with local channels) on and around the flanks of the rising salt diapir. More recently, successful stimulation of the Chalk Group, coupled with re-evaluation of core and well-log data, has indicated that economic production rates could also be achieved from the underlying fractured chalk reservoir.

Download Full-text

Improved seismic interpretation of a salt diapir by utilization of diffractions, exemplified by 2D reflection seismics, Danish sector of the North Sea

Interpretation ◽

10.1190/int-2018-0190.1 ◽

2020 ◽

Vol 8 (1) ◽

pp. T77-T88 ◽

Cited By ~ 1

Author(s):

Mahboubeh Montazeri ◽

Lars Ole Boldreel ◽

Anette Uldall ◽

Lars Nielsen

Keyword(s):

North Sea ◽

Seismic Imaging ◽

Seismic Velocity ◽

Velocity Model ◽

Salt Diapir ◽

The North ◽

Reflection Seismics ◽

The North Sea ◽

Sediment Layers

Development of salt diapirs affects the hydrocarbon trapping systems in the Danish sector of the North Sea, where the reservoirs mainly consist of chalk. Seismic imaging and interpretation of the salt structures are challenging, primarily due to the complex geometry of the salt bodies and typically strong velocity contrast with the neighboring sediment layers. The quality of seismic imaging in the North Sea is highly dependent on the quality of the estimated velocity model. We have studied diffracted arrivals originating from the salt flanks and adjacent sedimentary structures using a diffraction imaging technique. The diffracted waves carry valuable information regarding seismic velocity and the location of geologic discontinuities, such as faults, fractures, and salt delimitations. We apply a plane-wave destruction method to separate diffractions from our stacked data. We optimize imaging based on diffraction analysis by using a velocity continuation migration technique, which leads to an estimation of the optimum focusing velocity model. We determine that the diffraction-based approach significantly improves the seismic imaging adjacent to the salt diapirs and the neighboring layers when compared with a standard approach in which we mostly ignore the diffractions. The new poststack time-migrated results provide detailed information that optimizes our interpretation of the salt diapir itself (e.g., the width of the salt neck) as well as the sediment layers related to the rim synclines. Processing schemes such as prestack depth migration and full-waveform inversion may potentially provide high-resolution images of the salt structures. We only account for diffractions in nonmigrated stacked data to better constrain seismic velocity and improve imaging around the salt diapir. The obtained results are critical for reservoir characterization.

Download Full-text