Compaction and cementation control on bleaching in Triassic fluvial red beds, S-Germany

This study focusses on bleaching phenomena on the pore scale in an Olenekian (Upper Buntsandstein) sandstone quarry. The study area exposes a 10 m thick red sandstone body with up to cm-sized, greyish-white laminae in sandstones. Analyses focus on bleached and unbleached zones in the same cm-sized samples. Bleached zones show a larger grain size (by 27 μm), less compaction and a higher porosity (by 3 %). They also exhibit stronger cementation by all observed authigenic phases of quartz, illite, K-feldspar and to a minor extent dolomite. Calculated intergranular volumes and cementational porosity loss also correlate positively with bleaching. Meanwhile unbleached zones contain more ductile grains (e.g. micas, detrital clay, rock fragments like phyllites and plutonic rock fragments) and are affected by major porosity loss via compaction. Bleaching is related to primary features like grain size-selective lamination and associated higher permeability in coarse-grained laminae. It is also reliant onto an early framework stabilising cement phase, which keeps pathways open for uplift-related leaching of the detritus and few dolomite cements

Reservoir quality controls on Rotliegend fluvio-aeolian wells in Germany and the Netherlands, Southern Permian Basin – Impact of grain coatings and cements

Reservoir quality in sandstones can be a function of temperature, pressure, and chemical alterations over time. Some intrinsic properties of sandstones can additionally impact the evolution of reservoir quality. The detrital composition, depositional environment, and properties controlled thereby, dictate some of the diagenetic changes. Extrinsic processes, like external fluids, e.g. from hydrothermal events or dewatering of clay minerals, can additionally result in changes of reservoir quality. One of these properties are grain coatings on quartz grains, which can strongly affect pore cementation by quartz overgrowths. To predict and infer the quality of undrilled reservoirs, constraints are needed to predict their occurrence. We analyse two reservoir settings in the Southern Permian Basin and delineate the impact of depositional systems, lithologies, detrital and authigenic composition on reservoir quality and with regard to grain coatings. Results highlight the importance of diagenetic alterations and the source area in regards to burial development in different parts of the Southern Permian Basin. Samples from the Rotliegend Bahnsen Sandstone Member from Germany and the Slochteren Sandstone Formation from the Netherlands have been petrographically and petrophysically analysed and linked to depositional environments. Our data shows that the emplacement and presence of grain coating minerals cannot be simply linked to the depositional environment or processes controlled thereby (e.g. grain size and sorting), neither on a reservoir-, nor on a basin scale. The dissolution of alumosilicates additionally has no consistent impact on the authigenesis of chloritic grain coatings on the reservoir- or basin scale in this study. This implies the necessity of sample specific analyses and importance of the assessment of diagenetic alterations when analysing, modelling, or predicting reservoir quality in similar settings worldwide

Lateral variations of detrital, authigenic and petrophysical properties in an outcrop analog of the fluvial Plattensandstein, Lower Triassic, Central S-Germany

The lateral heterogeneity of reservoir rocks is important to assess storage potential and permeability. This case study focusses on a Lower Triassic (upper Olenekian) outcrop of fluvial sandstones of the Plattensandstein Member (Röt Formation) near Röttbach in the southern part of the Germanic Basin, southern Germany. The Buntsandstein Group is considered a suitable reservoir for thermal storage or exploration in southern Germany. In the Röttbach Quarry, the >10 m thick lithic arkoses are exposed over 35 m laterally in three adjacent walls and consist of two units separated by an erosive surface. They are covered by several metres of the Lower Röt Claystone Member. Using sedimentological logging, spectral gamma ray-, porosity- and permeability measurements as well as petrographic analyses calculating compaction parameters, lateral reservoir quality differences are studied. Sedimentary structures in the multi-storey channels suggest a point bar deposit. The migration direction of the channels correlates with deteriorating reservoir quality. This reduction in porosity and permeability correlates with an increased detrital mica and authigenic illite content, the occurrence of rip-up clasts and a lateral increase of gamma ray signatures by 19 API (avg. 5.0 vol% K, 2.7 ppm U, 11.9 ppm Th). The occurrence of larger amounts of mica and clay minerals is linked to decreasing flow velocities throughout the evolution of a meandering system. They enhance compaction and reduce available intergranular pore space. Permeability laterally deteriorates by up to three orders of magnitude (48 to 0.02 mD, avg. 9 mD) while measured porosities show minor variability (11 to 19 %, avg. 16 %). The deterioration of reservoir quality is related to compactional (COPL 11 to 28 %, avg. 18 %) and cementational porosity loss (CEPL 13 to 29 %, avg. 22 %) and is mainly controlled by detrital mica and authigenic illite

Compaction control on diagenesis and reservoir quality development in red bed sandstones: a case study of Permian Rotliegend sandstones

Authigenic minerals formed during diagenesis in conjunction with compaction by burial have long been known to lead to porosity-loss of sandstones, and a subsequent deterioration in reservoir quality. The diagenetic impact on reservoir quality and permeability heterogeneity measured horizontal and vertical to bedding was characterized in three fluvio-eolian Lower Permian Rotliegend outcrops from the Flechtingen High, the northern Hesse Basin (both Germany) and the Vale of Eden (UK) using point-counting, polarized light-microscopy, helium pycnometry and permeability measurements. Results show significant porosity (10 to 35%) and permeability (0.01 to 10,000 mD) ranges largely independent of depositional environ-ment. The major control on reservoir quality in Cornberg Sandstones are dolomite and siderite cementation in conjunction with illitization and illite and kaolinite cementation, leading together with quartz cementation to a mostly cemented IGV and poorest reservoir quality (avg. horizontal permeability: 0.96 mD). Flechtingen Sandstones are most intensely compacted due to the lack of significant early diagenetic cement phases and continuous illitic grain-to-grain coatings, which inhibited intense quartz cementation but enhanced chemical compaction at quartz grain contacts, resulting in intermediate reservoir quality (avg. horizontal permeability: 34.9 mD). Penrith Sandstones lack significant authigenic phases besides quartz due to carbonate dissolution during uplift. They show the least amount of detrital feldspars and clay minerals, leading to no major reservoir quality reduction by burial diagenetic clay mineral alterations, resulting in the highest reservoir quality (avg. horizontal permeability: 5900 mD). Additional results highlight higher horizontal to vertical permeability ratios kh/kv in less homogeneous sandstones of 1000 mD of 1. Although detrital and authigenic sample compositions vary throughout the studied areas, the general effect of grain coatings coverages on syntaxial cement inhibition and chemical compaction can be delineated. This study increases the understanding of porosity reduction in sandstones, as it confirms the necessity to differentiate between the illitic grain-to-grain coatings and illitic grain-to-IGV coatings. As a result, the enhancing effect of illite on chemical compaction on quartz grain-grain boundaries can be better constrained, as well as the effect of grain coatings on quartz cementation. This is relevant for res-ervoir quality and risk assessment in hydrocarbon and geothermal plays as well as in storage

Impact of grain coats on quartz overgrowth and Reservoir properties

Syntaxial overgrowth cementation, and thereby reservoir quality, can be affected by grain coating phases inhibiting nucleation. Reaction kinetics provide a means to model the development of cement phases over time. Additional algorithms constraining compaction behavior, porosity, and permeability development are used to model reservoir quality. Sub-vertical deformation bands can compartmentalize reservoirs by impacting bed-parallel permeability and preserve geochemical alterations

Modulated light potentials for state manipulation of quasiparticles in ultra-cold Bose gases

Ensembles of ultra-cold atoms have been proven to be versatile tools for high precision sensing applications. Here, we present a method for the manipulation of the state of trapped clouds of ultra-cold bosonic atoms. In particular, we discuss the creation of coherent and squeezed states of quasiparticles and the coupling of quasiparticle modes through an external cavity field. This enables operations like state swapping and beam splitting which can be applied to realize a Mach–Zehnder interferometer (MZI) in frequency space. We present two explicit example applications in sensing: the measurement of the healing length of the condensate with the MZI scheme, and the measurement of an oscillating force gradient. Furthermore, we calculate fundamental limitations based on parameters of state-of-the-art technology.H2020 Marie Skłodowska-Curie Actionshttps://doi.org/10.13039/100010665Peer Reviewe

Rock typing of diagenetically induced heterogeneities – A case study from a deeply-buried clastic Rotliegend reservoir of the Northern German Basin

Reservoir quality of sandstones is mainly derived from their permeability and porosity. As a result, porosity-reducing processes need to be understood in order to evaluate and model reservoir quality in sandstones. This case study from a Rotliegend gas reservoir in the Northern German Basin utilizes petrophysical measurements in conjunction with petrography in order to assess reservoir qualities and define rock types. The most significant diagenetic factors influencing the development of the IGV (intergranular volume) are quartz cementation due to low illite grain coating coverages on grain to IGV interfaces and chemical compaction due to pronounced illite grain coating coverages on grain to grain interfaces. Where large proportions of the interface between adjacent grains are coated by illite, stronger chemical compaction (pressure dissolution) was observed to occur. This chemical compaction reduces the IGV, and thus open pore space. Permeabilities measured under decreasing confining pressures from 50 to 2 MPa were used to determine the pressure sensitivities of permeability (David et al., 1994), which ranged from 0.005 to 0.22 MPa−1. The pressure sensitivity of permeability, porosity and permeability were linked to the petrographic texture, implying three different major rock types: Type A is characterized by an uncemented petrographic texture with high porosities (avg.: 9.8%), high permeabilities (avg.: 126 mD), and low pressure sensitivities of permeability (avg.: 0.019 MPa−1). Type B is intensely cemented with reduced porosities (avg.: 4.0%), reduced permeabilities (avg.: 0.59 mD), and increased pressure sensitivities of permeability (avg.: 0.073 MPa−1). Type C is characterized by intense chemical compaction leading to the lowest porosities (avg.: 1.8%) and permeabilities (avg.: 0.037 mD) in concert with the highest pressure sensitivity of permeability (avg.: 0.12 MPa−1). The heterogeneity induced by diagenesis will have an impact on recoverable resources and flow rates in both hydrocarbon and geothermal projects in similar siliciclastic reservoirs