95,422 research outputs found
Understanding the Impact of Open-Framework Conglomerates on Water-Oil Displacements: Victor Interval of the Ivishak Reservoir, Prudhoe Bay Field, Alaska
The Victor Unit of the Ivishak Formation in the Prudhoe Bay Oilfield is
characterized by high net-to-gross fluvial sandstones and conglomerates. The
highest permeability is found within sets of cross-strata of open-framework
conglomerate (OFC). They are preserved within unit bar deposits and assemblages
of unit bar deposits within compound (braid) bar deposits. They are thief zones
limiting enhanced oil recovery. We incorporate recent research that has
quantified important attributes of their sedimentary architecture within
preserved deposits. We use high-resolution models to demonstrate the
fundamental aspects of their control on oil production rate, water breakthrough
time, and spatial and temporal distribution of residual oil saturation. We
found that when the pressure gradient is oriented perpendicular to the
paleoflow direction, the total oil production and the water breakthrough time
are larger, and remaining oil saturation is smaller, than when it is oriented
parallel to paleoflow. The pressure difference between production and injection
wells does not affect sweep efficiency, although the spatial distribution of
oil remaining in the reservoir critically depends on this value. Oil sweep
efficiency decreases slightly with increase in the proportion of OFC
cross-strata. Whether or not clusters of connected OFC span the domain does not
visibly affect sweep efficiency.Comment: 27 pages including 14 figure
Specifics in the formation of substituence through in the Karvina part of the Ostrava-Karvina coalfield with the use radar interferometry
Deep extraction of minerals is accompanied by deformations of the strata overlying extracted
coal seams. Deformations of overlying layers run up to the surface where a subsidence trough
gradually forms. The movement of individual surface points is curvilinear, spatial and, in
relation to the time pattern, not uniform. In some cases, during the formation of a subsidence
trough, temporary uplifts of the surface occur. This paper gives a particular area in which uplifts
of the surface occurred when the rigid overlying strata was disturbed. The character of
deformations of the overlying rocks is evaluated on the basis of a comparison of the results of the
measurement of subsidence of the surface using geodetic methods with the development of
mined-out areas and with their extracted thickness. For specifying the time of failure of the
overlying strata, also information obtained from a system of continuous monitoring of seismic
events is used. The spatial extent of the subsidence trough is identified by satellite radar
interferometry (InSAR) techniques applied to TerraSAR-X images. The subsidence wave was
possible to detect using a short temporal difference of 11 days between satellite radar images.
This shows the potential of short-temporal high resolution InSAR for monitoring of progress of
subsidence troughs. A good knowledge of extents and shape of subsidence trough formation in
time allows to verify values of parameters used for prediction purposes. Application of the short
temporal InSAR appears very effective for spatio-temporal studies of the current subsidence
trough development and helps understanding the physical process as well as identifying
deviations from the behaviour expected by models.Web of Science13326926
Fingerprinting stress: stylolite and calcite twinning paleopiezometry revealing the complexity of progressive stress patterns during folding-the case of the Monte Nero anticline in the Apennines, Italy
In this study we show for the first time how quantitative stress estimates can be derived by combining calcite twinning and stylolite roughness stress fingerprinting techniques in a fold-and-thrust belt. First, we present a new method that gives access to stress inversion using tectonic stylolites without access to the stylolite surface and compare results with calcite twin inversion. Second, we use our new approach to present a high-resolution deformation and stress history that affected Meso-Cenozoic limestone strata in the Monte Nero Anticline during its late Miocene-Pliocene growth in the Umbria-Marche Arcuate Ridge (northern Apennines, Italy). In this area an extensive stylolite-joint/vein network developed during layer-parallel shortening (LPS), as well as during and after folding. Stress fingerprinting illustrates how stress in the sedimentary strata did build up prior to folding during LPS. The stress regime oscillated between strike slip and compressional during LPS before ultimately becoming strike slip again during late stage fold tightening. Our case study shows that high-resolution stress fingerprinting is possible and that this novel method can be used to unravel temporal relationships that relate to local variations of regional orogenic stresses. Beyond regional implications, this study validates our approach as a new powerful toolbox to high-resolution stress fingerprinting in basins and orogens combining joint and vein analysis with sedimentary and tectonic stylolite and calcite twin inversion techniques
Approaches to integrated strategic/tactical forest planning
Traditionally forest planning is divided into a hierarchy of planning phases. Strategic planning is conducted to make decisions about sustainable harvest levels while taking into account legislation and policy issues. Within the frame of the strategic plan, the purpose of tactical planning is to schedule harvest operations to specific areas in the immediate few years and on a finer time scale than in the strategic plan. The operative phase focuses on scheduling harvest crews on a monthly or weekly basis, truck scheduling and choosing bucking instructions. Decisions at each level are to a varying degree supported by computerized tools. A problem that may arise when planning is divided into levels and that is noted in the literature focusing on decision support tools is that solutions at one level may be inconsistent with the results of another level. When moving from the strategic plan to the tactical plan, three sources of inconsistencies are often present; spatial discrepancies, temporal discrepancies and discrepancies due to different levels of constraint. The models used in the papers presented in this thesis approaches two of these discrepancies. To address the spatial discrepancies, the same spatial resolution has been used at both levels, i.e., stands. Temporal discrepancies are addressed by modelling the tactical and strategic issues simultaneously. Integrated approaches can yield large models. One way of circumventing this is to aggregate time and/or space. The first paper addresses the consequences of temporal aggregation in the strategic part of a mixed integer programming integrated strategic/tactical model. For reference, linear programming based strategic models are also used. The results of the first paper provide information on what temporal resolutions could be used and indicate that outputs from strategic and integrated plans are not particularly affected by the number of equal length strategic periods when more than five periods, i.e. about 20 year period length, are used. The approach used in the first paper could produce models that are very large, and the second paper provides a two-stage procedure that can reduce the number of variables and preserve the allocation of stands to the first 10 years provided by a linear programming based strategic plan, while concentrating tactical harvest activities using a penalty concept in a mixed integer programming formulation. Results show that it is possible to use the approach to concentrate harvest activities at the tactical level in a full scale forest management scenario. In the case study, the effects of concentration on strategic outputs were small, and the number of harvest tracts declined towards a minimum level. Furthermore, the discrepancies between the two planning levels were small
Sampling design for compliance monitoring of surface water quality: A case study in a Polder area
International agreements such as the EU Water Framework Directive (WFD) ask for efficient sampling methods for monitoring natural resources. In this paper a general methodology for designing efficient, statistically sound monitoring schemes is described. An important decision is the choice between a design-based and a model-based method, implying the choice between probability (random) sampling and purposive sampling. For mapping purposes, model-based methods are more appropriate, whereas to obtain valid results for the universe as a whole, such as in testing water quality standards against legal standards, we generally prefer a design-based method. Four basic sampling patterns in space-time universe are described: static, synchronous, static-synchronous, and rotational. A case study is carried out for monitoring the quality of surface water at two farms in western Netherlands, wherein a synchronous sampling design is applied, with stratified simple random sampling in both space and time. To reduce laboratory costs the aliquots taken at the locations of a given sampling round are bulked to form a composite. To test the spatiotemporal mean N-total concentration during the summer half-year against the MAR standard with a power of 80% at a concentration 15% below the MAR standard and with a confidence of 95%, six to nine sampling rounds are needed with 50 to 75 locations per sampling round. For P-total the required number of sampling rounds differs strongly between the two farms, but is for both farms much larger than for N-total
Sampling design for compliance monitoring of surface water quality: A case study in a Polder area
International agreements such as the EU Water Framework Directive (WFD) ask for efficient sampling methods for monitoring natural resources. In this paper a general methodology for designing efficient, statistically sound monitoring schemes is described. An important decision is the choice between a design-based and a model-based method, implying the choice between probability (random) sampling and purposive sampling. For mapping purposes, model-based methods are more appropriate, whereas to obtain valid results for the universe as a whole, such as in testing water quality standards against legal standards, we generally prefer a design-based method. Four basic sampling patterns in space-time universe are described: static, synchronous, static-synchronous, and rotational. A case study is carried out for monitoring the quality of surface water at two farms in western Netherlands, wherein a synchronous sampling design is applied, with stratified simple random sampling in both space and time. To reduce laboratory costs the aliquots taken at the locations of a given sampling round are bulked to form a composite. To test the spatiotemporal mean N-total concentration during the summer half-year against the MAR standard with a power of 80% at a concentration 15% below the MAR standard and with a confidence of 95%, six to nine sampling rounds are needed with 50 to 75 locations per sampling round. For P-total the required number of sampling rounds differs strongly between the two farms, but is for both farms much larger than for N-total
Biodiversity patterns of free-living marine nematodes in a tropical bay: Cienfuegos, Caribbean Sea
Spatial and temporal biodiversity patterns of free-living marine nematodes were studied in Cienfuegos
Bay, a tropical semi-enclosed basin in the Caribbean Sea. Taxonomic (to species level) and functional
(biological trait) approaches were applied for describing the assemblage structure and relating it to
abiotic environment based on a sampling scheme in six subtidal stations and three months. Biological
trait approach added relevant information to species pattern regarding relationships between diversity
patterns and the abiotic environment. The most common morphotypes were deposit feeding nematodes,
with colonising abilities of 2–3 (in a scale from 1 to 5), tail conical cylindrical or filiforme and body
slender; and their abundance were correlated with depth, organic matter and silt/clay fraction. In spite of
a high turnover of species, functional diversity of assemblages did not change notably in space and time.
A result probably due to sampling of the habitat pool of species and to low heterogeneity of the studied
muddy bottoms. Chemical pollution (organic enrichment and heavy metals) and hydrodynamic regime
possibly drove the biodiversity patterns. Spatial distribution of assemblages support the existence of two
well differentiated basins inside the bay, the northern basin more polluted than the southern one. The
low hydrodynamic regime would determine a poor dispersion of nematodes resulting in high spatial
variance in the assemblage structure; and also the associated hypoxic conditions and pollutants in
sediments can explain the dominance of tolerant nematode species such as Daptonema oxycerca, Sabatieria
pulchra, Terschellingia gourbaultae, and Terschellingia longicaudata. A comparison of spatial–
temporal patterns of biodiversity between Cienfuegos Bay and other semi-enclosed bays in temperate
regions suggests several similarities: nematode assemblages are strongly influenced by anthropogenic
disturbance, temporal trends are weak or overridden by spatial ones, and few cosmopolitan genera/
species tolerant to pollution and hypoxic conditions are dominant
Estimating space-time mean concentrations of nutrients in surface waters of variable depth
A monitoring scheme has been designed to test whether the space-time mean concentration total Nitrogen (N-total) in the surface water in the Northern Frisian Woodlands (NFW, The Netherlands) complies with standards of the European Water Framework directive. Since in statistical testing for compliance monitoring valid estimators for the mean and its variance are important, a design-based method is preferred above a model-based method. In the NFW-area the surface water depth varies in both space and time and can periodically equal zero, due to variation in precipitation and evapotranspiration. To account for this, space-time mean concentrations are estimated by the ratio of the estimated total mass of nutrient and the estimated total volume of water. The method is applied in the period from 1 April to 30 September 2008 to four hydrologically different subareas. Besides, the aim was to use the information on the spatial and temporal variance of N-total concentrations to optimize the numbers of sampling rounds and sampling locations per sampling round in future monitoring campaigns, given budgetary constraints. A bootstrap procedure was applied to account for uncertainty about the temporal and spatial variances in estimating the optimal number of sampling rounds and sampling locations. For two subareas the accuracy of the estimated space-time means can be improved by sampling more frequently at less locations (compared to the design applied in 2008), whereas for one subarea sampling less frequently at more locations increases the precision. For one subarea the sample data were rather inconclusive about the optimal sample sizes
A soil sampling program for the Netherlands
Soil data users in The Netherlands were inventoried for current and future data needs. Prioritized data needs were used to design the Netherlands Soil Sampling Program (NSSP) as a framework containing 3 groups of related projects: map upgrading, map updating and upgrading of pedotransfer functions. In each one group, the sampling design, performance criteria and optimal sample size were defined. This paper focuses on the upgrading of the existing soil map of The Netherlands at scale 1:50,000, and extensively treats the user inventory and the sampling strategy. The sampling design, performance criteria of the sampling and associated optimal sample size were obtained by statistical analysis of soil data available before the sampling. The Phosphate Sorption Capacity (PSC) was chosen as target variable to optimize sampling, because it dominated total cost per sample. A prior analysis of a performance criterion related to the sampling error of PSC resulted in a cost saving of 13% relative to total cost determined earlier by expert judgment. A posterior analysis showed that the set quality criterion was reached or better in 6 out of 7 cases. The NSSP resulted in a data base with soil data from 2524 sample points selected by stratified random sampling, and a collection of 5764 aliquots taken at these points. The NSSP has been showing its usage potential for various kinds of environmental studies and could be a sound future basis for a national scale monitoring program
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