The Erskine Field, Block 23/26, UK North Sea

2003 ◽  
Vol 20 (1) ◽  
pp. 523-535 ◽  
Author(s):  
R. N. Coward
Keyword(s):  
Lacustrine Environment ◽  
East Central ◽  
Shallow Marine ◽  
Western Margin ◽  
Permeability Characteristics ◽  
Fine Grained ◽  
Delta Plain ◽  
Porosity And Permeability ◽  
Shale Formation ◽  
High Temperature High Pressure

AbstractThe Erskine Field is a high temperature, high pressure (HTHP), gas condensate accumulation located on the western margin of the East Central Graben. The field was discovered in 1981 by the 23/26a-3RE well and subsequently delineated by six appraisal wells. Development approval was granted in 1995 and to date five development wells have been drilled. In December 1997, Erskine Field became the first HTHP field in the UKCS to achieve production. Hydrocarbons are produced from three separate Jurassic reservoirs. In order of decreasing importance, these are: the Late Oxfordian Erskine Sandstone (Puffin Formation), the Middle Jurassic Pentland Reservoir, and the Late Oxfordian Heather Turbidite Reservoir.The Erskine Sandstone is very fine to fine-grained highly bioturbated, shaley sandstone. The sandstones represent shallow marine progradational sequences, deposited predominantly in the offshore transition zone. Within the majority of the Erskine Sandstone, porosity is high (20-25%) but with relatively poor associated permeability (0.1-10mD). However, the tops of the coarsening upward sequences (E30 and E70 zones) have appreciably better permeability and are thought to be the major conduits for fluid flow. The E30 and E70 zones would not have been identified, had it not been for the extensive coring programme undertaken in the development wells.The Pentland Reservoir is a regionally extensive sequence of interbedded sandstone, shales, coals and siltstones, deposited in a fluvial-lacustrine environment in a delta plain setting. Permeability in the Pentland reservoir (0.1 mD-1 D) is in general far superior to the values observed in the Erskine Sandstone. The main control on the observed variability in porosity and permeability characteristics is grain size, that in turn is controlled by facies.The Heather Turbidite Reservoir occurs within two thin predominantly fine-grained turbidite sandstone beds in the Heather Shale Formation. This reservoir is restricted to the Alpha Terrace region in the SW of the field, and is drained by a single development well.Total Erskine Field reserves are estimitated at approx 400 BCF of gas and 66 MMBBL of condensate.

The role of clay minerals in influencing porosity and permeability characteristics in the Bridport Sands of Wytch Farm, Dorset

Clay Minerals ◽  
1982 ◽  
Vol 17 (1) ◽  
pp. 41-54 ◽  
Author(s):  
K. A. Morris ◽  
C. M. Shepperd
Keyword(s):  
Clay Minerals ◽  
Mixed Layer ◽  
Oil Recovery ◽  
Pore Space ◽  
Water Injection ◽  
Lower Jurassic ◽  
Core Material ◽  
Permeability Characteristics ◽  
Fine Grained ◽  
Porosity And Permeability

AbstractThe Bridport Sands is a widespread marine sandstone of Lower Jurassic age found in much of southern England. It is a very fine grained, moderately sorted quartz-arenite and is characterized by the alternation of friable and hard calcareous-cemented layers. The sands form the upper reservoir in the Wytch Farm Field, Dorset, which is currently producing at the rate of around 4000 barrels per day. Investigation of core material to assess the suitability of water injection for gas/oil recovery has shown that significant reductions of liquid permeability compared to air permeability occur. These reductions vary from 30% or less in the best quality reservoir to more than 70% in low-permeability sandstones. Clay minerals in the Bridport Sands comprise mainly kaolinite and mixed-layer clays of both the illite-chlorite and illite-smectite types. Small amounts of vermiculite and chlorite also occur. The kaolinite is found as loosely-attached, discrete particles, whilst the mixed-layer clays form patchy pore linings. The permeability reductions may be explained by: (i) the adsorption of water and expansion of poorly-crystalline mixed-layer illite-smectites causing blockage of pore space (this reduction is largely reversible) and (ii) the physical movement of authigenic kaolinite crystal aggregates blocking pore-throats (this reduction is largely non-reversible). The pore-size distribution, clay particle sizes, the distribution of the clays within the pore space, and the composition of the clays are all important factors in controlling porosity/permeability relationships and permeability reductions in the friable reservoir intervals in the Bridport Sands.

Overpressure Identification Using The Eaton Method on The Gumai Formation of Geragai Graben, Jambi Sub Basin

2020 ◽  
Author(s):  
A. O. Marnila
Keyword(s):  
Pressure Data ◽  
Stratigraphic Sequence ◽  
Fine Grained ◽  
Marine Sedimentation ◽  
Plot Analysis ◽  
Significant Reversal ◽  
Porosity And Permeability ◽  
Upper Level ◽  
Type Data ◽  
Fine Grained Sand

Geragai graben is located in the South Sumatera Basin. It was formed by mega sequence tectonic process with various stratigraphic sequence from land and marine sedimentation. One of the overpressure indication zones in the Geragai graben is in the Gumai Formation, where the sedimentation is dominated by fine grained sand and shale with low porosity and permeability. The aim of the study is to localize the overpressure zone and to analyze the overpressure mechanism on the Gumai Formation. The Eaton method was used to determine pore pressure value using wireline log data, pressure data (RFT/FIT), and well report. The significant reversal of sonic and porosity log is indicating an overpressure presence. The cross-plot analysis of velocity vs density and fluid type data from well reports were used to analyze the causes of overpressure in the Gumai Formation. The overpressure in Gumai Formation of Geragai graben is divided into two zones, they are in the upper level and lower level of the Gumai Formation. Low overpressure have occurred in the Upper Gumai Formation and mild overpressure on the Lower Gumai Formation. Based on the analyzed data, it could be predicted, that the overpressure mechanism in the Upper Gumai Formation might have been caused by a hydrocarbon buoyancy, whereas in the Lower Gumai Formation, might have been caused by disequilibrium compaction as a result of massive shale sequence.

scholarly journals Reservoir quality and its controlling diagenetic factors in the Bentiu Formation, Northeastern Muglad Basin, Sudan

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yousif M. Makeen ◽  
Xuanlong Shan ◽  
Mutari Lawal ◽  
Habeeb A. Ayinla ◽  
Siyuan Su ◽  
...  
Keyword(s):  
Clay Content ◽  
Petroleum Exploration ◽  
Reservoir Quality ◽  
Burial Depth ◽  
Petroleum Reservoir ◽  
Fine Grained ◽  
Porosity And Permeability ◽  
Negative Role ◽  
Crevasse Splay ◽  
Channel Deposits

AbstractThe Abu Gabra and Bentiu formations are widely distributed within the interior Muglad Basin. Recently, much attention has been paid to study, evaluate and characterize the Abu Gabra Formation as a proven reservoir in Muglad Basin. However, few studies have been documented on the Bentiu Formation which is the main oil/gas reservoir within the basin. Therefore, 33 core samples of the Great Moga and Keyi oilfields (NE Muglad Basin) were selected to characterize the Bentiu Formation reservoir using sedimentological and petrophysical analyses. The aim of the study is to de-risk exploration activities and improve success rate. Compositional and textural analyses revealed two main facies groups: coarse to-medium grained sandstone (braided channel deposits) and fine grained sandstone (floodplain and crevasse splay channel deposits). The coarse to-medium grained sandstone has porosity and permeability values within the range of 19.6% to 32.0% and 1825.6 mD to 8358.0 mD respectively. On the other hand, the fine grained clay-rich facies displays poor reservoir quality as indicated by porosity and permeability ranging from 1.0 to 6.0% and 2.5 to 10.0 mD respectively. A number of varied processes were identified controlling the reservoir quality of the studies samples. Porosity and permeability were enhanced by the dissolution of feldspars and micas, while presence of detrital clays, kaolinite precipitation, iron oxides precipitation, siderite, quartz overgrowths and pyrite cement played negative role on the reservoir quality. Intensity of the observed quartz overgrowth increases with burial depth. At great depths, a variability in grain contact types are recorded suggesting conditions of moderate to-high compactions. Furthermore, scanning electron microscopy revealed presence of micropores which have the tendency of affecting the fluid flow properties in the Bentiu Formation sandstone. These evidences indicate that the Bentiu Formation petroleum reservoir quality is primarily inhibited by grain size, total clay content, compaction and cementation. Thus, special attention should be paid to these inhibiting factors to reduce risk in petroleum exploration within the area.

Lithofacies, Depositional Environment and Diagenetic Evolution of the Paleocene Patala Formation, Potwar Basin, Pakistan: Implication for Shale Gas Potential

2021 ◽  
Author(s):  
Nasar Khan ◽  
Rudy Swennen ◽  
Gert Jan Weltje ◽  
Irfan Ullah Jan
Keyword(s):  
Organic Matter ◽  
Shale Gas ◽  
Gas Reservoirs ◽  
Shallow Marine ◽  
Anoxic Conditions ◽  
Fine Grained ◽  
Potwar Basin ◽  
Diagenetic Evolution ◽  
Reservoir Assessment ◽  
Gas Potential

<p><span><strong>Abstract:</strong> Reservoir assessment of unconventional reservoirs poses numerous exploration challenges. These challenges relate to their fine-grained and heterogeneous nature, which are ultimately controlled by depositional and diagenetic processes. To illustrate such constraints on shale gas reservoirs, this study focuses on lithofacies analysis, paleo-depositional and diagenetic evolution of the Paleocene Patala Formation at Potwar Basin of Pakistan. Integrated sedimentologic, petrographic, X-ray diffraction and TOC (total organic carbon) analyses showed that the formation contained mostly fine-grained carbonaceous, siliceous, calcareous and argilaceous siliciclastic-lithofacies, whereas carbonate microfacies included mudstone, wackestone and packstone. The silicious and carbonaceous lithofacies are considered a potential shale-gas system. The clastic lithofacies are dominated by detrital and calcareous assemblage including quartz, feldspar, calcite, organic matter and clay minerals with auxiliary pyrites and siderites. Fluctuations in depositional and diagenetic conditions caused  lateral and vertical variability in lithofacies. Superimposed on the depositional heterogeneity are spatially variable diagenetic modifications such as dissolution, compaction, cementation and stylolitization. The δ</span><sup>13</sup><span>C and δ</span><sup>15</sup><span>N stable isotopes elucidated that the formation has been deposited under anoxic conditions, which relatively enhanced the preservation of mixed marine and terrigenous organic matter. Overall, the Patala Formation exemplifies deposition in a shallow marine (shelfal) environment with episodic anoxic conditions.</span></p><p><strong>Keywords</strong><strong>:</strong> Lithofacies, Organic Matter, Paleocene, Potwar Basin, Shale Gas, Shallow Marine.</p>

scholarly journals Granite micro-porosity changes due to fracturing and alteration: secondary mineral phases as proxies for porosity and permeability estimation

2018 ◽  
Author(s):  
Martin Staněk ◽  
Yves Géraud
Keyword(s):  
Mercury Intrusion Porosimetry ◽  
Fluorescent Light ◽  
Fracture Density ◽  
Void Space ◽  
Mercury Intrusion ◽  
Fine Grained ◽  
Mineral Phases ◽  
Space Geometry ◽  
Porosity And Permeability ◽  
The Difference

Abstract. Several alteration facies of fractured Lipnice granite are studied in detail on borehole samples by means of mercury intrusion porosimetry, polarized and fluorescent light microscopy and microprobe chemical analyses. The goal is to describe the granite void space geometry in vicinity of fractures with alteration halos and to link specific geometries with simply detectable parameters to facilitate quick estimation of porosity and permeability based on e.g. drill cuttings. The core of the study are results of porosity and throat size distribution analyses on 21 specimens representing unique combinations of fracture-related structures within 6 different alteration facies basically differing in secondary phyllosilicate chemistry and porosity structure. Based on a simple model to calculate permeability from the measured porosities and throat size distributions the difference in permeability between the fresh granite and the most fractured and altered granite is 5 orders of magnitude. Our observations suggest that the porosity, the size of connections and the proportion of crack porosity increase with fracture density, while precipitation of iron-rich infills as well as of fine grained secondary phyllosilicates acts in the opposite way. Different styles and intensities of such end-member agents shape the final void space geometry and imply various combinations of storage, transport and retardation capacity for specific structures. The study also shows the possibility to use the standard mercury intrusion porosimetry with advanced experimental setting and data treatment to distinguish important differences in void space geometry within a span of few per cent of porosity.

Correlation of the Waco Member of the Alger Shale Formation (Silurian; Llandovery; Telychian) in east-central Kentucky and south-central Ohio

GFF ◽  
2014 ◽  
Vol 136 (1) ◽  
pp. 254-258 ◽  
Author(s):  
Nicholas B. Sullivan ◽  
Carlton E. Brett ◽  
Patrick I. McLaughlin ◽  
Mark A. Kleffner ◽  
Bradley D. Cramer
Keyword(s):  
East Central ◽  
South Central ◽  
Shale Formation

Arumberiamorph structure in modern microbial mats: implications for Ediacaran palaeobiology

2017 ◽  
Vol 188 (1-2) ◽  
pp. 5 ◽  
Author(s):  
Anton V. Kolesnikov ◽  
Taniel Danelian ◽  
Maxime Gommeaux ◽  
Andrey V. Maslov ◽  
Dmitriy V. Grazhdankin
Keyword(s):  
Microbial Mats ◽  
Biological Response ◽  
Early Cambrian ◽  
Shallow Marine ◽  
Delta Plain ◽  
Microbial Biofilms ◽  
Environmental Perturbations ◽  
The Village ◽  
Globally Distributed ◽  
Marine Basins

In the course of studying modern halotolerant microbial mats in salterns near the village of Kervalet, western France, we observed fanning-out and curved series of macroscopic ridges on the surface of a newly formed biofilm. The structure resembles the late Ediacaran fossil Arumberia which is globally distributed in Australia, Avalonia, Baltica, Siberia and India, always confined to intertidal and delta-plain settings subject to periodic desiccation or fluctuating salinity. Although the origin of the structure observed in modern microbial mats remains enigmatic, wrinkled and rugose variants of microbial biofilms in general exhibit increased levels of resistance to several environmental stresses. By analogy, the fossil Arumberia could be interpreted as a microbial mat morphotype (the “Arumberia” morph) developed in response to environmental perturbations in terminal Ediacaran shallow marine basins. If environmental conditions are likely to be responsible for the formation of Arumberia, it is not that a specific biological community has survived since the Ediacaran – it is that the biological response of microbial communities that manifested itself quite commonly in certain terminal Ediacaran and early Cambrian environments can still be found (seemingly in much more restricted settings) today.

Nature, genesis and industrial properties of the kaolin from Masirah Island, Oman

Clay Minerals ◽  
2017 ◽  
Vol 52 (3) ◽  
pp. 275-297 ◽  
Author(s):  
Bernhard Pracejus ◽  
Iftikhar Ahmed Abbasi ◽  
Salah Al-Khirbash ◽  
Mohammad Al-Aamri
Keyword(s):  
Ceramic Materials ◽  
Raw Material ◽  
Sulfide Deposit ◽  
High Plasticity ◽  
Shallow Marine ◽  
Secondary Minerals ◽  
Fine Grained ◽  
Coastal Marine ◽  
Mode Of Occurrence ◽  
Industrial Use

AbstractKaolin deposits >10 m thick overlie unconformably a Mesozoic ophiolite sequence at Jabal Humr, Masirah Island, Oman. The clay's mineralogical and chemical composition, plasticity and moisture content were measured to determine its genesis and suitability for commercial usage. The clay-rich raw material contains 76–94% kaolinite and varying amounts of quartz (micro sheets coating kaolinite) and calcite as well as secondary sulfates. The mode of occurrence, an associated shallow-marine iron oolite/pisolite unit, various secondary minerals which can only form in a gossan environment (oxidation zone of a much older sulfide deposit), and minerals such as gypsum that are highly unstable within a laterite, have led to the conclusion that the Jabal Humr kaolinite deposit cannot have the lateritic origin that has been suggested previously. Rather, it must have formed in a coastal marine environment with a subsequent strong geochemical overprint from the underlying gossan environment, after being enveloped by Tertiary carbonates. A high plasticity and its light colour after firing indicate that this material is suitable for industrial use, especially in pottery. Occasional high contents of up to ∼25% extremely fine-grained quartz (sheet-like, <50 nm thick) reduce the need for quartz addition during the processing for ceramic materials; such natural kaolinite-quartz mixtures already produce a suitable blend of materials. The possible occurrence of spalling during or after firing, caused by the sporadic presence of accessory calcite, can be avoided by by further addition of quartz which leads to the formation of calcium silicate.

Almandine garnet phenocrysts in a ~1 Ga rhyolitic tuff from central India

2008 ◽  
Vol 146 (1) ◽  
pp. 133-143 ◽  
Author(s):  
SARBANI PATRANABIS-DEB ◽  
JUERGEN SCHIEBER ◽  
ABHIJIT BASU
Keyword(s):  
Central India ◽  
Mineral Chemistry ◽  
Triple Junctions ◽  
Fine Grained ◽  
Mineral Inclusions ◽  
Major Oxide ◽  
Shale Formation ◽  
Igneous Zircon ◽  
Compositional Variability ◽  
Lower Crustal

AbstractWe report on the newly discovered almandine garnet phenocrysts in rhyolitic ignimbrites (Sukhda Tuff) in the Precambrian Churtela Shale Formation of the Chhattisgarh Supergroup in central India. SHRIMP ages of igneous zircon from the ignimbrites range from 990 Ma to 1020 Ma. These ignimbrites exhibit characteristic eutaxitic texture with compacted curvilinear glass shards with triple junctions. Quartz (commonly embayed; bluish cathodoluminescence) and albite (altered but retaining ghosts of twinning) are common phenocrysts; others are apatite, ilmenite, rutile, magnetite, zircon, monazite and garnet. There are no metamorphic or granitic xenoliths in the ignimbrites. Garnet grains occur as isolated broken isotropic crystals with sharp or corroded boundaries in a very fine-grained groundmass of volcanic ash that consists principally of albite, quartz, magnetite and glass. They do not have any systematically distributed inclusions. A few have penetratively intergrown phenocrysts of apatite, ilmenite, rutile and zircon, which we interpret as subophitic texture. Extensive SEM-BSE imaging of more than 100 grains and electron microprobe traverses across about 30 grains showed no zoning or systematic compositional variability. Common (metamorphic) garnets are usually zoned with respect to Fe–Mg–Mn and typically have mineral inclusions. We infer, therefore, that these observed garnets are not metamorphic xenocrysts. The average major oxide composition of analysed garnets from five different horizons within the Sukhda Tuff, spanning approximately 300 m of the stratigraphic section, have very small standard deviation for each element, which is suggestive of a single magmatic source. Phenocrysts of quartz, including those in contact with coexisting garnets, show blue scanning electron CL, indicating rapid cooling from high temperature; this suggests that adjacent coexisting garnets are not slowly cooled restites. We conclude, on the basis of texture, mineral chemistry and absence of any indicative xenoliths or xenocrysts, that these almandine garnets (Al78.7Py12.3Gr7.4Sp1.6) are phenocrysts within the Sukhda Tuff. Almandine of such composition is stable under high pressure. We infer that almandine crystallized at lower crustal depths in a magma that ascended very rapidly and may have erupted explosively.

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