bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrocarbon occurrence and exploration in and around igneous rocks
Authors: Schutter Stephen R. 
Published: April 2008

Abstract
Hydrocarbons can occur within and around igneous rocks, sometimes in commercially significant quantities. Igneous or closely associated rocks can be hydrocarbon sources in the conventional sense (biotic) as well as possibly through abiotic processes. Maturation is extremely variable, depending on the extrusive/intrusive nature of the activity and the relative importance of a deep heat source. Igneous volatiles and hydrothermal fluids may also be important in mobilizing and moving hydrocarbons. Igneous rocks can have good reservoir qualities, and they can produce their own trapping structures as well as being part of a larger feature. Many exploration methods are individually unreliable in and around igneous rocks, and an integrated approach is most effective. Seismic, magnetotelluric, gravity and magnetic surveys may all provide helpful information. Geological mapping, geochemistry and remote imagery may also be helpful. Evaluation of potentially commercial hydrocarbon accumulations requires interpretation of well logs, which may have unusual characteristics. Drill stem and production tests may also be needed for evaluation before exploration ends and development begins.
Volcanic reservoir rocks of northwestern Honshu island, Japan
Authors: Magara Kinji 
Published: April 2008

Abstract
The main Japanese oil producing region lies on the Japan Sea side of northern Honshu island. Although the total reserve is small and production supplies only threetenths of a percent of total Japanese oil consumption, it has two distinguishing features: (1) the main reservoir rocks are volcanic, pyroclastic, or tuffaceous, and (2) primary oil and gas migration seems to have taken place downward from the overlying source rocks. Marine volcanic activity since 15 Ma formed the main reservoir sections together with significant secondary porosity development. Thick and continuous deposition of organic-rich shales and mudstones followed and lower parts of these fine-grained rocks became the main source rocks. The principal direction of primary hydrocarbon migration occurred vertically downward from them. These fine-grained rocks seem to have acted as pressure seals as well as capillary seals over the oil/gas saturated zones below.
Controls on primary porosity and permeability development in igneous rocks
Authors: Petford Nick 
Published: April 2008

Abstract

Some of the more important processes leading to the development of primary igneous porosity due to the cooling and crystallization of magma are reviewed. A distinction is made between volcanic and plutonic rocks, and crystalline and granular volcanic material. Porosity in each rock type is classified according to a proposed effective length scale and geometry into diffusive (Class D) and macroscopic flow (Class F) features. Estimated ranges in values of porosity and permeability are given for a wide selection of igneous rock types, and comparison is made with permeability variations (Δ
k
) derived for both the continental and oceanic crust. While fracture porosity is dominant in most crystalline materials, primary porosity development may play an important role in the final (total) porosity in igneous basement. Some types of primary porosity and permeability in igneous rocks will be strongly time- and scale-dependent due to thermal effects associated with the emplacement and cooling of magmas and volcanic material. Tectonic reworking of the primary petrophysical properties of basement-forming igneous rocks may be significant in the development of regions of anisotropy and enhanced porosity.
Characterization of rough-walled fractures in crystalline rocks
Authors: Ogilvie S. R. , Isakov E. , Taylor C. W. , Glover P. W. J. 
Published: April 2008

Abstract
The full characterization of the rough surfaces of fractures and their resulting apertures is an important step in the drive toward an improved understanding of the factors which control fluid flow through rocks. This is crucial in igneous and metamorphic rocks, since fractures in these rocks may form the only significant pathways for fluid migration. Here we describe a three-pronged approach for the full characterization of rough fracture surfaces in a selection of crystalline rocks using a suite of software developed in house. Firstly, profiling is carried out using an optical method, which converts images of epoxy fracture surfaces covered with dyed water into topographies using the Lambert-Beer Law. Many hardware and software (OptiProf™) developments give this method the upper hand over previous attempts at spectrophotometric analysis. It is not possible to profile every fracture surface, therefore numerical modelling of fluid flow is carried out using synthetic fractures with rough fracture surfaces that are representative of the natural rock fractures. ParaFrac™ allows the analysis and parametrization of fracture surfaces and apertures. SynFrac™ enables the numerical synthesis of fracture surfaces and apertures with prescribed basic parameters. Both procedures take full account of the complex matching properties of the fracture surfaces as a function of wavelength, as well as anisotropy within the properties defining the fracture surfaces and their resulting aperture. They have been rigorously tested on a large suite of synthetic fractures as well as real rock fractures. These tests have allowed relationships between the standard deviation of surface asperity heights, the fractal dimension and the matching parameters to be related to the resulting aperture of the fractures.
Thermally induced primary fracture development in tabular granitic plutons: a preliminary analysis
Authors: Koenders M. A. , Petford Nick 
Published: April 2008

Abstract

We present an analytical model that predicts some of the mechanical effects associated with the intrusion and subsequent cooling of a rectangular intrusion emplaced at a uniform temperature into elastic continental crust. Assuming an idealized geometry and initial conditions, we recover the temperature field and subsequent strain field as a function of both position and time. The strain field is particularly relevant as it provides information on the
primary
(cooling-related) fracture formation pattern and direction within and immediately surrounding the pluton. We find a large strain jump across the pluton-country rock contact, implying that fracture formation should be maximized at the edges and corners of the intrusion. The direction of the fractures is predominantly vertical within the pluton centre, but becomes progressively more inclined towards the pluton margin and into the adjacent country rock. Fracture orientation may depend critically on the geometry of the intrusion, in particular the ratio of the longest to shortest dimension
L
1
/
L
2
.
Applications of X-ray computed tomography in the geosciences
Authors: Mees F. , Swennen R. , Geet M. Van , Jacobs P. 
Published: April 2008

Abstract
X-ray computed tomography (CT) is a non-destructive technique with wide applications in various geological disciplines. It reveals the internal structure of objects, determined by variations in density and atomic composition. Large numbers of parallel 2D sections can be obtained, which allows 3D imaging of selected features. Important applications are the study of porosity and fluid flow, applied to investigations in the fields of petroleum geology, rock mechanics and soil science. Expected future developments include the combined use of CT systems with different resolutions, the wider use of related X-ray techniques and the integration of CT data with results of compatible non-destructive techniques.
Porosity and fluid flow characterization of granite by capillary wetting using X-ray computed tomography
Authors: Géraud Y. , Surma F. , Mazerolle F. 
Published: April 2008

Abstract

The porosity and transfer properties of a very low porosity material (granite) are measured. A new procedure is defined using a capillary test and X-ray computed tomography (CT) scanning. Injected volumes are very low, i.e. a few cm
3
for a sample volume of 1 dm
3
, using a fluid/rock ratio lower than 0.1%. This technique allows monitoring of the anisotropy of fluid flow during the test. Flow along the injection direction is higher than along the perpendicular direction. Saturation depends on the specific saturation of each mineral zone. Multiscale analysis allows defining the flow conditions as being controlled at both the mineral and the sample scale. Results indicate the specific role for various constituting parts of the material. High speed flow occurs in the crack network of K-feldspar, while the storage function is localized in the reaction zone forms by quartz and muscovite.
Characterization by X-ray computed tomography of water absorption in a limestone used as building stone in the Oviedo Cathedral (Spain)
Authors: Ruiz de Argandoña V. G. , Rodriguez-Rey A. , Celorio C. , Calleja L. , Suárez del Rio L. M. 
Published: April 2008

Abstract
Water plays a fundamental role in rock weathering processes. Its penetration and movement inside rocks greatly influences the nature and intensity of damage affecting building stones. X-ray computed tomography (CT) is a useful technique for non-destructive mapping of water penetration. For the reported study, CT was used to investigate the internal structure and water penetration patterns for the Piedramuelle Stone, a Cretaceous limestone used as building material in the Oviedo Cathedral (North of Spain).
X-ray CT provides good images of the internal structure of the samples: the sedimentary layering due to differences in composition and porosity is clearly seen, as well as other textural features. The movement and penetration rate of water was monitored during standard free absorption water tests. The images that were obtained show a clear difference between dry and wet zones in the interior of the sample. Water movement is related to the petrographic characteristics of the rock, mainly to layering which controls the direction of water penetration. Hounsfield Unit numbers provide a quantitative approach for assessing the penetration rate of water.
Estimation of porosity and hydraulic conductivity from X-ray CT-measured solute breakthrough
Authors: Anderson S. H. , Wang H. , Peyton R. L. , Gantzer C. J. 
Published: April 2008

Abstract
Heterogeneities are common in natural porous media and are present on different scales. Use of X-ray computed tomography (CT) may provide a tool for quantifying smallscale heterogeneities in porosity and hydraulic conductivity in porous media. Porosity and saturated hydraulic conductivity distributions were estimated using CT for a series of undisturbed soil core samples taken from a field site. CT measurements were collected during breakthrough experiments using an iodide tracer. Techniques were developed to estimate porosity and hydraulic conductivity from solute breakthrough data. Results were compared with bulk sample measurements. CT-measured porosity compared well with laboratory-measured porosity. Hydraulic conductivity estimated from CT methods slightly overestimated laboratory-measured values. These techniques provide a method to quantify the spatially variable porosity and hydraulic conductivity on a millimetre scale rather than on a core-averaged scale. Chemical transport through the soil was predicted using a finite element method for each core using the CT-measured soil properties. Comparisons between measured and predicted chemical transport suggest that small-scale heterogeneities cause departures between measured and simulated solute breakthrough curves, and that a smaller grid size may be needed to improve the simulation.
Industrial X-ray computed tomography studies of lake sediment drill cores
Authors: Flisch A. , Becker A. 
Published: April 2008

Abstract
An industrial X-ray computed tomography (CT) system was used for the study of sedimentary and deformation structures in weakly consolidated late Pleistocene and Holocene lake sediments. CT analysis revealed details of structures that could not be detected by X-ray radiography or visual core logging. Examples include sand dykes, dropstones and plant remains, which are potentially important in palaeoseismological and palaeoenvironmental research. The CT images also help to discriminate between drill core artefacts and natural structures. X-ray tomography was also used for the determination of physical properties, particularly for bulk density measurements based on calibrated grey-scale values.
Analysis of analogue models by helical X-ray computed tomography
Authors: Schreurs G. , Hänni R. , Panien M. , Vock P. 
Published: April 2008

Abstract
The aim of analogue model experiments in geology is to simulate structures in nature under specific imposed boundary conditions using materials whose rheological properties are similar to those of rocks in nature. In the late 1980s, X-ray computed tomography (CT) was first applied to the analysis of such models. In early studies only a limited number of cross-sectional slices could be recorded because of the time involved in CT data acquisition, the long cooling periods for the X-ray source and computational capacity. Technological improvements presently allow an almost unlimited number of closely spaced serial cross-sections to be acquired and calculated. Computer visualization software allows a full 3D analysis of every recorded stage. Such analyses are especially valuable when trying to understand complex geological structures, commonly with lateral changes in 3D geometry. Periodic acquisition of volumetric data sets in the course of the experiment makes it possible to carry out a 4D analysis of the model, i.e. 3D analysis through time. Examples are shown of 4D analysis of analogue models that tested the influence of lateral rheological changes on the structures obtained in contractional and extensional settings.

Supplementary material:
The nineteen movies referred to in the article are available at
https://doi.org/10.6084/m9.figshare.c.4788519
Tubular structures of northern Wairarapa (New Zealand) as possible examples of ancient fluid expulsion in an accretionary prism: evidence from field and petrographical observations
Authors: Ledésert Béatrice , Buret Christophe , Chanier Frank , Ferrière Jacky , Recourt Philippe 
Published: April 2008

Abstract

The Cape Turnagain area is located on the inboard portion of the Hikurangi subduction margin, on the northern Wairarapa coast of the North Island of New Zealand. A 4.5 km long coastal section of sea cliffs of Mio-Pliocene sediments contains numerous tubular carbonate-rich concretions. Their morphology and petrographical observations suggest they were possibly formed by fluid flows of carbonate-rich water through a silty sediment. These tubular concretions could be fossil fluid expulsion structures similar to dewatering chimneys described offshore in New Zealand. The external diameter of the concretions observed
in situ
reaches 60 cm and internal canal up to 4 cm. Up to four canals are encountered in a single concretion. A positive relationship is observed between the chimney size and the number of canals or cumulative diameter of canals, suggesting that the size of the concretion is a function of the fluid which flowed through the plumbing network. The increased number of tubular concretions in upper Miocene siltstones compared to overlying Pliocene strata could be linked to a compressive event that caused overpressuring and the expulsion of fluids through the sediment pile.
Fluidization structures produced by upward injection of sand through a sealing lithology
Authors: Hurst Andrew , Cartwright Joe , Duranti Davide 
Published: April 2008

Abstract

Subsurface and outcrop data are used to describe sand injectites, a group of genetically related features that includes sandstone dykes and sills, but also structures within depositional sand bodies. Fluidization is identified as the process by which sand is injected but we draw attention to the lack of constraints regarding fluidization velocity and fluid viscosity. Injectites are shown to develop between <10 m and 500 m below the seafloor. No relationship between depth of generation and injection geometry is found. Liquefaction of sand may produce sufficient excess pore fluid to create small sand injections during shallow burial. Large injectite bodies are identified on seismic data that may exceed 4 × 10
7
m
3
are unlikely to be related to sand liquefaction. The general validity of hydraulic fracture as the mechanism for seal failure and propagation of injections is questioned. The association between the formation of polygonal faults and sand injection provides one of several alternative mechanisms for seal failure. Multi-phase intrusion is proposed as a likely mechanism for the formation of large sand intrusions, both because of the cyclical nature of most of the process invoked in their formation, and the author’s own observations. Many of the processes of sand injection remain poorly constrained.
The geometry, growth and linkage of faults within a polygonal fault system from South Australia
Authors: Nicol A. , Walsh J.J. , Watterson J. , Nell P.A.R. , Bretan P. 
Published: April 2008

Abstract
Quantitative analysis of faults within a South Australian polygonal fault system, interpreted from a 3-D onshore seismic survey, provides a basis for establishing their growth and linkage histories. The geometric characteristics of faults are consistent with an origin arising from the gravitational instability of an underlying low-density, overpressured, mobile layer. Fault size populations have scale-bound, non-power-law properties reflecting the thicknesses of the faulted and mobile layers and the strongly connected nature of the system. The spatial distributions of faults reflect the localization of conjugate faults at the top of the mobile layer and the scale of fault-bounded polygons. Displacement variations on faults show marked decreases at or adjacent to the top of the mobile layer and attest to its active role in faulting. The wide range of fault strike directions provides numerous fault intersections with high intersection angles (≥ 60°) forming triple-junctions at which fault linkage and capture occurred. Fault linkage and capture is attributed to a simple model in which continued movement on faults which share a mutual footwall is favoured and hanging wall faults are deactivated. The model involves thickening of the mobile layer within the footwalls of faults and thinning and eventual grounding of the overlying sequence, within their hanging walls.
Polygonal faults in the Ormen Lange Field, Møre Basin, offshore Mid Norway
Authors: Stuevold Liv M. , Faerseth Roald B. , Arnesen Linn , Cartwright Joe , Möller Nicola 
Published: April 2008

Abstract
3D seismic and well data from the Ormen Lange Field, Mid Norway have been used to analyse the development of a system of polygonal faults affecting the Late Cretaceous-early Paleocene reservoir. These faults have the typical properties of polygonal fault systems recognized elsewhere in mainly fine-grained successions. They grew by upward propagation from the thick, shale-prone interval of the Late Cretaceous in the Møre Basin and were reactivated during the deposition of the Balder Formation. They have throws ranging from a few metres to 80 m, are typically 1–3 km in length and have highly irregular throw distributions along strike, mainly as a result of complex fault intersection geometries. The Ormen Lange Field is the first described example of polygonal faults that completely transect a major sandstone reservoir interval. The presence of these faults has important implications for the likely production behaviour of the field. Fault seal analysis shows that they are unlikely to form juxtaposition seals, except locally, but that they may have a significant risk for clay smear seals, particularly in the lower reservoir unit.
Normal faulting in chalk: tectonic stresses vs. compaction-related polygonal faulting
Authors: Hibsch C. , Cartwright J. , Hansen D.M. , Gaviglio P. , André G. , Cushing M. , Bracq P. , Juignet P. , Benoit P. , Allouc J. 
Published: April 2008

Abstract
This paper documents normal fault sets observed in chalks exposed in widely separated localities in the UK and France. These faults are characterized by having a wide range of strikes at any one locality, are developed entirely within the chalk succession and do not seem to interconnect to deeper or shallower structures. These structures may result from two different mechanisms: (1) complex polyphase deformational histories involving contrasting stress states; or (2) a single deformational phase in which the faults develop to accommodate compactional strains. Evidence is presented from microstructural and petrographic data to support the latter interpretation. In particular, the association of calcite and marcasite mineralizations with fracture surfaces and fault zones and textural observations relating flint occurrence to early fault formation point towards fault propagation at a very early stage of burial and compaction of the chalky sediments. An analogy is drawn between these outcrop-scale structures and polygonal fault systems at a larger scale recognised from seismic observations of chalk sequences deposited at passive continental margins. The origin of these structures may be related to syneresis at an early stage of deformation followed by pressure solution phenomena that may reactivate this early-inherited polygonal fault pattern until the present day.
The origin and development of joints in the Boom Clay Formation (Rupelian) in Belgium
Authors: Mertens J. , Vandenberghe N. , Wouters L. , Sintubin M. 
Published: April 2008

Abstract
A system of natural, vertical and mutual perpendicular joints is described in the clay pits of the Rupelian Boom Clay in the Antwerp area of North Belgium. Joints are the dominant discontinuity surfaces in the clay outcrops. Neither the stress evolution of the clay during burial and uplift nor the regional tectonic history can explain the tensional jointing. It is suggested that the negative horizontal stresses required for the joint formation in clays are caused by shrinkage of the clay when the formation was located near the surface. The origin of the loss of pore fluid in a several tens of metres thick clay layers remains unknown. The joints in the Boom Clay are a scarce field example of the possibility of lateral contraction of a clay layer, without involving tectonics or burial/uplift as an origin. When such a jointed clay layer is buried again, the presence of the vertical joints might offer pathways for fluid migration through a relatively impermeable layer. A general relationship between a maximal depth beneath which no tensional joints can occur and the cohesion of the clay has been derived. In the case of the Boom Clay this limiting depth is around 40–50 m. The time of the joint formation in the outcrop area is most probably late Oligocene/early Miocene. The burial history of the clay at a particular location can be used as a predictive tool for the presence or absence of tensional joints.