Influence of mobile salt on the distribution and preservation of Fulmar reservoir sands in the UK central north sea

AbstractThe Triassic of the Central North Sea is a continental succession that contains prolific hydrocarbon-bearing fluvial sandstone reservoirs stratigraphically partitioned by mudstones. Within the Skagerrak Formation of the UK sector, hydrocarbon accumulations in the Judy, Joanne and Josephine Sandstone members are top sealed by the Julius, Jonathan and Joshua Mudstone members, respectively. However, UK and Norwegian stratigraphic correlations have been problematical for decades, largely due to biostratigraphic challenges but also due to the non-uniqueness of the lithotypes and because the cross-border stratigraphic nomenclature differs and has yet to be rationalized. This study focuses on mudstones rather than sandstones to unify cross-border correlation efforts at a regional scale. The mudstone members have been characterized by integrating sedimentological, petrophysical and geophysical data. The facies are indicative of playa lakes that frequently desiccated and preserved minor anhydrite. These conditions alternated with periods of marshy, palustrine conditions favourable for the formation of dolostones. Regional correlations have detected lateral facies changes in the mudstones which are important for their seismically mappable extents, resulting palaeogeographies and, ultimately, their competency as intraformational top seals. Significant diachroneity is associated with the lithological transitions at sandstone–mudstone member boundaries and although lithostratigraphic surfaces can be used as timelines over short distances (e.g. within a field), they should not be assumed to represent timelines over longer correlation lengths. Palaeoclimatic trends are interpreted and compared to those of adjacent regions to test the extent and impact of climate change as a predictive allogenic forcing factor on sedimentation. Mudstone member deposition occurred as a result of the retreat of large-scale terminal fluvial systems during a return to more arid ‘background’ climatic conditions. The cause of the member-scale climatic cyclicity observed within the Skagerrak Formation may be related to volcanic activity in large igneous provinces which triggered the episodic progradation of fluvial systems.

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The MacCulloch Field, Block 15/24b, UK North Sea

Geological Society London Memoirs ◽

10.1144/gsl.mem.2003.020.01.37 ◽

2003 ◽

Vol 20 (1) ◽

pp. 453-466 ◽

Cited By ~ 1

Author(s):

C. Gunn ◽

J. A. MacLeod ◽

P. Salvador ◽

J. Tomkinson

Keyword(s):

North Sea ◽

Water Contact ◽

Northern Flank ◽

Recoverable Reserves ◽

Average Porosity ◽

Oil Water ◽

The Witch ◽

The Uk ◽

Clay Formation ◽

Central North Sea

AbstractThe MacCulloch Field lies within Block 15/24b in the UK Central North Sea and is located on the northern flank of the Witch Ground Graben. It was discovered by Conoco well 15/24b-3 in 1990.MacCulloch Field is a four-way dip closure at Top Paleocene over a deeper Mesozoic structure. The reservoir consists of Upper Balmoral Sandstones containing 32-37° API oils derived from Kimmeridge Clay Formation shales and sealed by shales belonging to the Sele Formation. The field contains recoverable reserves of 60-90 MMBOE.Reservoir quality is generally very good, with an average porosity of 28% and core permeabilities (Kh) between 200 mD and 2D. AVO anomalies and a seismic flat spot are associated with oil filled reservoir and the oil-water contact in certain areas of the field.

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The Huntington discoveries: efficient exploration in the UK Central North Sea

Geological Society London Petroleum Geology Conference series ◽

10.1144/0070213 ◽

2010 ◽

Vol 7 (1) ◽

pp. 213-223 ◽

Cited By ~ 2

Author(s):

J. M. Hollywood ◽

R. C. Olson

Keyword(s):

North Sea ◽

Efficient Exploration ◽

The Uk ◽

Central North Sea

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Field map

Geological Society London Memoirs ◽

10.1144/gsl.mem.2003.020.01.map3 ◽

2003 ◽

Vol 20 (1) ◽

pp. 132-132

Keyword(s):

North Sea ◽

Oil And Gas ◽

Median Line ◽

Moray Firth ◽

The Uk ◽

Central North Sea ◽

International Border

AbstractMap depicting the position and names of the main oil and gas producing fields located in the Viking Graben and eastern parts of the Outer Moray Firth rift arms, Northern and Central North Sea. The international border (median line) between the UK and Norway is highlighted as are the producing fields in the Norwegian sector. The boxed areas show the extent of licensed acreage in the region.

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The Machar Field, Block 23/26a, UK North Sea

Geological Society London Memoirs ◽

10.1144/m52-2018-45 ◽

2020 ◽

Vol 52 (1) ◽

pp. 523-536 ◽

Cited By ~ 2

Author(s):

Zoë Sayer ◽

Jonathan Edet ◽

Rob Gooder ◽

Alexandra Love

Keyword(s):

North Sea ◽

Debris Flows ◽

Water Injection ◽

Salt Diapir ◽

Reservoir Quality ◽

Complex Interplay ◽

Light Oil ◽

High Matrix ◽

The Uk ◽

Central 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.

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Exploration well failures from the UK North Sea

Geological Society London Petroleum Geology Conference series ◽

10.1144/pgc8.3 ◽

2016 ◽

Vol 8 (1) ◽

pp. 267-272 ◽

Cited By ~ 2

Author(s):

Christian J. H. Mathieu

Keyword(s):

Peer Review ◽

North Sea ◽

Primary Reason ◽

Success Rates ◽

Moray Firth ◽

The Uk ◽

Central North Sea ◽

Exploration Well ◽

Play Context

AbstractThe UK Oil & Gas Authority carried out post-well failure analyses of exploration and appraisal wells in the Moray Firth and the UK Central North Sea to fully understand the basis for drilling the prospects and the reasons why the prospects failed.The data consisted of Tertiary, Mesozoic and Palaeozoic targets/segments associated with 97 wells drilled from 2003 to 2013. Seal was the primary reason for failure followed by trap, reservoir and charge. Root causes for failure were a lack of lateral seal, the absence of the target reservoir and the lack of a trap. The main pre-drill risk was not accurately predicted in over one-third of the cases and a third of the segments were targeted on the basis of perceived Direct Hydrocarbon Indicators.This study identified a number of interpretation gaps and pitfalls that ultimately contributed to the well failures. These included poor integration, improper application of geophysics, lack of regional play context, and absent or ineffective peer review. Addressing these gaps in a comprehensive and systematic way is fundamental to improving exploration success rates.

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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.

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