A Call for Standards in the CO 2 Value Chain Neerup, Randi; Løge, Isaac A; Helgason, Kári ...
Environmental science & technology,
12/2022, Letnik:
56, Številka:
24
Journal Article
The Siri Canyon has proved to be a perfect area for investigating various morphologies of diagenetic silica in sandstones. The development in silica morphologies can be observed from very shallow (∼
...1700
m) to increased burial depth (∼
3000
m) and increased proximity to the Central Graben (distance from 0 to 65
km). Hydrocarbons and pore fluids, now found in the Siri Fairway, have (at least partly) originated from the Central Graben.
The Siri Canyon is a submarine canyon system eroded into the uppermost chalk deposits and filled with Palaeogene hemipelagic and turbiditic marls and mudstones interbedded with sandstone units deposited from sandy mass-flows and sandy turbidites, which originated on the Stavanger Platform. Several hydrocarbon exploration and production wells have been drilled in the Siri Canyon, seven of which are included in this study (Nini-3, Nini-1, NA-2P, Sofie-1, Siri-4, Celilie-1A and Augusta-1). The reservoir sandstones in these wells all contain authigenic silica of various morphologies identified with a combination of traditional optical microscopy and scanning electron microscopy.
The silica morphologies in some places are classic and well-documented in the literature, whereas others, at least to our knowledge, have never previously been described. Some of the silica morphologies presented here show gradual transition from one to another, and others are stand-alone forms without clear relationships to other forms.
The silica morphologies can be expressed in the following way:
1.
Opal rims; characteristic of the initial phase of the silica diagenesis in most sandstone units in the Siri Canyon. Thick opal rims characterise the sandstone parts adjacent to the mudstone units in the Stine segment of the Siri Field.
2.
Microquartz (quartz crystals with a size of 1–5
µm); seen as coatings on the opal rims, both ordered and random.
3.
Cavity overgrowth; found as quartz outgrowths in circular and angular cavities formed by dissolution of early authigenic phases. Angular cavities in the microquartz coatings origin from dissolution of clinoptilolite, possibly with a source in volcanic ash, whereas dissolution of lepispheres probably resulted in circular cavities.
4.
Quartz ridges (syntaxial quartz overgrowths, a few micro millimetre in width, in parallel lines — defined in this paper).
5.
Quartz mountains (syntaxial, irregular 5–10
µm large quartz crystals — defined in this paper); developed in the water-filled sandstone intervals where fluids from the Central Graben were introduced, possibly together with the hydrocarbon, and where the continued growth was not retarded by the presence of hydrocarbons in the pore fluids.
6.
Macroquartz (syntaxial quartz overgrowths >
20
µm); seen as continued growths from quartz mountains. This takes place in the deeper reservoir sandstones, promoted by fluids originating from the Central Graben and increased burial depth.
7.
Quartz with sutured grain contacts; occurring only in the deepest well (3000
m).
The Hermod sand of the Stine Segments, Siri Field, Danish North Sea, displays large permeability variations (1–600
mD). These permeability variations represent horizontal layering in the reservoir, ...largely formed by diagenetic processes. They have a significant impact on reservoir performance, because horizontal producers in fairly thin reservoirs (∼30
m) are protected against bottom-water influx and can produce water-free for long periods of time.
This paper presents the results of a detailed multidisciplinary study where the observed variation in permeability can be explained by two main diagenetic phases: silica, as opal cement and microquartz, and berthierine, a serpentine mineral that is closely related to chlorite.
Opal/microquartz and berthierine cements dominate in separate parts of the reservoir bodies. Opal/microquartz cemented sands have high permeability (typically 500–600
mD). Berthierine cement has a different growth pattern in the oil and water zones, resulting in intermediate permeability in the oil zone (typically 50–100
mD) and very low permeability in the water zone (typically 1–10
mD).
Detrital glaucony in the Palaeogene glauconitic sandstones in Siri Canyon, Danish North Sea, has been analysed from 15 exploration wells by X‐ray diffraction, electron microprobe and scanning ...electron microscopy. These sandstones consist of mixed‐layer illite/smectite and have a large variability in chemical composition and structure. In the most shallow wells (ca 1700 m), the glaucony is rich in Fe and consists of mixed‐layer illite/smectite with random‐interstratification (R = 0). In the depth interval from 1700 to 2000 m, the composition changes as Si is incorporated. The structure changes to ordered R = 1. Further increase in burial leads to the loss of Fe. Ordered R = 3 mixed‐layer illite/smectite is recognized from burial depths of 2200 m. The proportion of illite in illite/smectite mixed layers increases only slightly with depth and temperature. Although the structural changes generally are associated with chemical changes, they can also take place isochemically when the detrital glaucony is tightly embedded in earlier cement, which prevented chemical exchange. The glaucony transformation in the Siri Canyon sandstones partly reflects a supply of Si and partly significant loss of Fe. Thus, the glaucony transformation relates to the general diagenesis of the host sandstone. These sandstones are cemented by microquartz at an early stage, followed by precipitation of Fe‐rich grain‐coating berthierine or chlorite.
Elemental geochemistry of 1131 sandstone samples has been used to characterise five Palaeogene sandstone members in a system of density flow deposits within an incised submarine canyon, Danish North ...Sea. Diagenetic overprinting has complicated the use of most main and trace elements, but a group of “heavy mineral bound” elements with low mobility (Ti, Y, Zr, Nb and Th) has proved highly potential for correlation. The individual sandstone members exhibit very consistent relations between the “heavy mineral elements” along the canyon and, based on Zr/Ti plots, two families of sandstone members can be distinguished. The families are recognised on variations in inclination and intersection of linear regression lines which are related to subtle variations in provenance/source area. The inclination is believed to be controlled by the detrital heavy mineral (HM) suite and composition, whereas the intersections are controlled by the background contribution, such as HM inclusions in detrital rock forming minerals, e.g. quartz and/or feldspar, as well as substituted and/or adhered elements in glauconite. The correlation pattern has been used to suggest a re-interpretation of the stratigraphic relation of some of the sands.
The submarine Siri Canyon is NE–SW-oriented and located in the Danish North Sea (Fig. 1). It contains a number of oil reservoirs with glauconite-rich sand. The reservoirs of interest in the Nini oil ...field are the Late Paleocene Tyr Member of the Lista Formation and the Kolga Member of the Sele Formation (Schiøler et al. 2007), presumably of Early Eocene age. These members have previously been known as the Ty and Hermod members (Hamberg et al. 2005; Poulsen et al. 2007). The sand shows signs of injection, both in cores and in seismic data. The aim of this work is to chemically characterise and fingerprint the sand in order to reveal the origin of the sand found in three horizontal wells, which could have been injected from one or both of the Tyr and Kolga members. Core samples were collected from two vertical wells of known stratigraphy to make a basis of comparison, whereas samples of the cuttings were collected from the three horizontal wells with ages primarily corresponding to the Kolga Member. The purpose was moreover to evaluate whether cuttings samples can be used for fingerprinting as an alternative to core samples.
A high-resolution spectral gamma-ray (SGR) log is compared to elemental whole rock geochemical data in a reservoir scale outcrop analogue, the Otter Sandstone Formation (Sherwood Sandstone Group), ...east Devon. SGR data compare closely to those generated for point samples by inductively coupled plasma (ICP) techniques, with disparities attributable to the different sample volumes. ICP data reveal separate mineralogical sources for radio-elements, which enable three lithotypes to be discriminated using Th/U ratio and K
2O data. Once established, the discriminants are applied to the SGR log enabling three lithotypes to be dicriminated. These conclusions suggests that SGR logs have significant potential for real-time lithotype prediction in continental sequences, which in turn enable predictions of reservoir quality, and increase confidence in the interpretation of sedimentary architecture.
Palaeoenvironmental interpretation in desert and evaporitic sediments is often ambiguous. Consequently, the recognition of primary sedimentary structures that indicate subaerial exposure or shallow ...marine conditions are therefore of crucial importance when interpreting marginal sedimentary evaporite facies. Parabolic halite dunes, described here for the first time, are observed on the salt crust of the largest salt flat in the world, the Salar de Uyuni in Bolivia. The halite dunes are relatively small (0.7–1.3 m in width and length), well-defined lobate to hemicyclic parabolic dunes, and are formed directly on the salt crust. A model describing the formation and migration of the dunes in relation to brine level and climatic conditions is presented.
A multi-disciplinary study of the dominantly fluvial Lower Triassic Otter Sandstone Formation (east Devon, UK) is presented. The approach integrates a variety of methods including sedimentology, ...conventional heavy mineral analysis, single grain microprobe analysis and elemental whole rock geochemistry (ICP-AES and ICP-MS). A species-level conventional heavy mineral study is compared to a whole rock geochemical analysis for the corresponding samples to investigate whether or not heavy mineral compositions can be discriminated from elemental whole rock data. The comparison provides sufficient evidence that the absolute and relative abundance of some of the heavy minerals; apatite, iron–titanium oxides, monazite and zircon can be discriminated geochemically. The established element–mineral relationships are used to construct both synthetic heavy mineral assemblages and synthetic heavy mineral index values from the geochemical data, which show considerable similarity to those of the conventional heavy mineral analysis. The presented synthetic heavy mineral logs display intraformational packages that enable subdivision of this barren continental succession. Furthermore, the observed subdivision is correlatable over a considerable distance when extended into the offshore Wessex Basin. The chemical approach unquestionably lacks the sensitivity of conventional heavy mineral analysis, however, by comparison it is rapid. This novel approach demonstrates that synthetic heavy mineral stratigraphy based, as here, on a well constrained stratotype has considerable potential for creating high-resolution correlations in both outcrops and the subsurface and may be of significant value to people working with reservoir characterisation.
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