Volcanic rocks can host significant hydrocarbon resources but are poorly understood in terms of their reservoir properties: especially their porosity and permeability characteristics. Basaltic lavas and volcaniclastic outcrops around Tenerife and basaltic lava flows from the Large Igneous Provinces of the Deccan Traps and the Faroe Islands were studied as potential “reservoir analogues” to compare with existing hydrocarbon discoveries in volcanic rocks. These studies together with the analysis of subsurface samples from South America permitted the geochemical and petrophysical properties of several volcanic reservoir analogues to be examined. Field observations of flow morphology and continuity of defined lava flow facies, were integrated with conventional core porosity and permeability measurements and the results of a micro-focus X-ray tomography (µCT) study to characterize the petrophysical properties of various volcanic rocks. Application of µCT allows the quantification and 3D visualisation of the pore space down to a µm scale and thus provides unprecedented insights into pore morphologies. When combined with traditional petrographic observations, this provides a powerful tool with which to analyse porosity development. Vesicles and fractures are the principle controls upon effective porosity development with permeability often controlled by the degree of vesiculation. Samples with vesicle densities greater than 20 % show significantly higher permeabilities and higher effective porosities due to the increased degree of vesicle coalescence forming connected networks. Individual lava flows can be divided into base, core and top facies, with lava piles comprising repeated cycles of these distinct facies. The best reservoir quality occurs in basalt flow tops (mean µCT ? = 21.85%) where vesicular porosity dominates. Reservoir quality significantly decreases in the tight flow cores, where primary porosity is controlled by cooling joints (fracture porosity) and inter-crystalline micro-porosity (mean µCT ? = 2.32%). Flow bases show variable reservoir potential due to the presence of breccia and/or vesiculation, depending upon the eruption environment (e.g. subaerial v subaqueous) and original geochemistry (e.g. acidic v basaltic) of the lava (mean µCT ? = 9.70%). The most porous horizons are the flow tops of each successive lava flow, whilst connectivity (permeability) between these horizons is via primary cooling joints or secondary fractures. Volcaniclastic lithologies of, tuff, ignimbrite, scoria and pumice, have the highest porosity and permeability (mean µCT ? = 48.09%). Distribution of the various volcanic facies is influenced by the magma chemistry, cooling rate and mode of eruption. The primary porosity and the permeability of the rocks may be subsequently modified either to create additional porosity and permeability by tectonic fracturing and dissolution during burial or weathering, or occlude porosity through the precipitation of secondary minerals and the alteration of primary minerals. Given volcanic rocks can exhibit high porosity (especially within flow top internal zones and to as lesser extent flow bases) these lithologies can form viable reservoirs. The stacking of successive flows results in a layer cake stratigraphy, with the more porous and permeable flow tops and bases separated by relatively impervious flow cores. Should sufficient fractures and cooling joints exist, then these reservoir horizons will be in communication with each other, permitting charging of hydrocarbons. The conclusion of this thesis is that despite low permeabilities, volcanic rocks are good hydrocarbon prospects, and understanding the distribution of these key internal zones and their characteristic porosities and permeabilities will enhance hydrocarbon exploration within these unconventional reservoirs.

Recent <i>in situ</i> measurements of volatiles (H₂O, Cl, F) within lunar melt inclusions, glass beads, and the mineral apatite have challenged the previously held notion that the Moon is depleted in volatiles. As the most widespread volatile-bearing phase, apatite has been the focus of many studies aiming to constrain the volatile inventory of the lunar interior. The thermodynamics of volatile partitioning into apatite, however, are poorly constrained. Here, Apollo mare basalts were investigated to provide an accurate composition for which apatite is found to crystallize under lunar conditions. This composition was used high temperature, high pressure experiments which constrained volatile partitioning between apatite and silicate melt. Combining experiments from this study, and those of the literature, an empirical model was developed to back-calculate melt volatile contents, at the time of apatite formation. Conservative estimates and preliminary findings suggest the amount volatiles in the at the time of apatite crystallization is highly variable but ranges up to 3.6 wt.% H2O, 5 wt.% F and 5.3 wt.% Cl. One of the reasons volatiles contents, in apatite and melt, vary so much is likely a result of degassing, as apatite is a late-stage mineral formed after ~95% melt solidification. Degassing, under lunar conditions, utilizing low-Ti and high-Ti compositions was constrained experimentally. The results from this investigation suggest that degassing is melt composition dependant and, as such, requires a thorough investigation of late-stage melt pockets to determine the amount of degassing that may occur prior to apatite growth. In addition, vapor-phase interaction was found to also alter volatile contents and δ³⁷Cl isotope signatures in apatites from Apollo 14 samples. This vapor-phase is thought to be from volatile-release during a major impact event, similar to other old (<i>sim</i>4 Ga) samples found on the lunar nearside. To constrain whether this process was a global phenomenon samples from regions previously unexplored (including the lunar farside) are required. A mission scenario, optimising sample return from Schödinger basin is proposed here where volcanics and potentially mantle material could be collected. These samples would provide key insight into indigenous lunar mantle volatile contents and global differentiation processes.

Unconventional petroleum of fine-grained rocks has become an interesting field of study and respectively source rocks turned to excellent reservoirs for petroleum generation and accumulation. Exploration and production from fine-grained rocks, such as shale, contemporaneous with technology advancement facilitated black shale use and made them cost benefit. This thesis deals with estimation of unconventional petroleum potential of Paleozoic fine-grained rocks in Poland and investigation of Purbeck rocks in southern England as natural laboratory analogues for unconventional petroleum characterisation. Geochemical results of black shale and limestone samples from the Holy Cross Mountains (HCM) in Poland were used as a proxy to estimate the unconventional petroleum potential of Paleozoic rock successions. Additionally, investigations of oil impregnated shales and limestones in Dorset provided analogues for understanding unconventional petroleum behaviour in tight limestone reservoirs. The rock samples were analysed using total organic carbon content (TOC), Rock-Eval pyrolysis, Gas Chromatography-Mass Spectrometry (GC-MS), Pyrolysis-GC-MS, and X-ray diffraction. Geochemical analyses indicate that the organic matter from the Polish Paleozoic samples in the HCM area were sourced mainly from marine sources and partially from terrestrial inputs that are poorly preserved and possess little potential for hydrocarbon generation. Devonian and some Silurian rocks, however, have good generation potential and can be considered as potential source rocks. The depositional conditions were mixed between oxic and anoxic and settings varied from shallow marine to deep marine along Baltica. There is a substantial change in organic contents and depositional environments across the Ordovician-Silurian boundary due to Hirnantian glacial events and subsequent deglaciation and transgressions. Organic matter increases across the boundary as a result of organic productivity caused by an upwelling system and marine transgressions subsequently changed the shallow marine environments to deeper water settings. The organic matter of the Paleozoic successions in the HCM is composed of type II or mixed type II/III kerogen that has a variable maturity ranging from marginal maturity to peak mature levels. The mineralogical composition of the studied shale and limestone samples in the HCM comprises quartz, carbonates, and clay minerals. Cambrian samples are generally poor in quartz and contain high amounts of clay minerals. Ordovician, Silurian, and Carboniferous shales contain high amounts of brittle minerals convenient for artificial stimulation although a few samples contain about 40 % clay minerals. The Devonian, one Carboniferous sample, and Permian samples are composed of carbonate minerals (calcite and dolomite) with small amounts of quartz. In terms of unconventional petroleum, the analysed rock samples in the outcrops and quarries cannot be considered as potential targets because TOC, maturity, mineralogy, or shale thickness would not fulfil the minimum requirement. However, the Devonian black shales could be regarded as oil shales but have limited potential due to thin nature of the beds. Existence of more interested fine-grained rocks in terms of unconventional investigations might be possible in areas, outside of the HCM, towards Carpathian Foredeep and NE of the HCM owing to the structural setting of the area. Non-impregnated black shales and limestones analysed from the Purbeck Group across Dorset, southern England indicate that there are lateral variations in distribution of organic compounds and depositional conditions. Marine, freshwater, and terrestrial organic matter was found in the samples and higher amounts of organic matter was preserved in central parts of the studied area where anoxic conditions and water column stratification were prevalent. The organic matter did not enter the oil window and exhibit immaturity or marginal maturity. Although freshwater was flowing from the west, paleosalinity was high in the west and decreased towards the east where marine incursions changed the water salinity. Freshwater and terrestrial organic materials were contributed from north and west of the studied area by the rivers and seasonal run offs from the hinterlands as a result of sea level fluctuations, local tectonic uplift, and climate changes. Some of the black shales and limestones of the Purbeck Group in Dorset were impregnated with oil and exhibit variations in oil chemistry. High amounts of oil staining were recorded in the shales with partial impregnation in the limestones, mostly along their contacts with the shales. Mixed sources of organic matter was found in the samples relating to autochthonous lacustrine (fresh-brackish water) organic materials indigenous to the Purbeck rocks and marine organic matter from migrated hydrocarbons. Two different maturity levels were found in the samples, immaturity for the autochthonous organic matter and peak oil window maturity for migrated hydrocarbons sourced from Lias rocks. Molecular characterisation revealed that there are different biodegradation levels between the shales and limestones, with moderate to heavy biodegradation levels in the shales and light biodegradation levels in the limestones, in particular for the limestones above the shale bed. Biodegradation levels increase westward across the area and at greater distances within the limestones surrounding the shales. Four different types of hosts for oil impregnation in the limestones were documented which include pores, fractures, matrix, and gastropod shells. Oil chemistry and its characteristics are different between hosts of varying sizes and volumes. Oil staining was highest in large pore spaces and large gastropod shells and was dominated by polar constituents; the limestone matrix was the least stained host in which aliphatic fractions prevailed. The oil in the hosts was biodegraded to different levels, moderate to heavy degrees in large pore spaces and fractures and light level in the matrix and small gastropod shells providing a composition more or less similar to the original composition of the migrated oil.

In this thesis we have performed an experimental investigation on the impact of rock heterogeneity on solute spreading and mixing in porous rock using X-ray tomography. Furthermore, we have created a numerical model based on experimentally obtained statistical rock descriptions to investigate the impact of transport and chemical heterogeneity on reactive transport. We present a new core-flood test to characterize solute transport in 3-D natural-rock media. The test is carried out for three rocks with an increasing level of heterogeneity: Berea sandstone, Ketton carbonate and Indiana carbonate. The impact of heterogeneity on solute transport is analysed by: 1., quantifying spreading and mixing using metrics such as the transverse dispersion coefficient, the dilution index, and the scalar dissipation rate, and 2., visualizing and analysing flow structures such as meandering, flow-focusing and flow-splitting. The transverse dispersion coefficient, Dt, and the variation in Dt throughout the rock core, increases with Peclet number (Pe) and rock heterogeneity. The dilution index and scalar dissipation rate indicate that mixing is Fickian for the Berea sandstone and Ketton carbonate, but diverges for the Indiana carbonate. Heterogeneous rock features are observed to cause meandering, focusing or splitting of the plume depending on Pe. The impact of transport and chemical heterogeneity on reactive transport is investigated by modelling the injection of a HCl solution into the three rocks. The model shows that both transport and chemical heterogeneity are important and the dominating factor depends on the transport regime and reaction kinetics. The model is able to capture different dissolution regimes: compact dissolution is observed for low injection rates while the onset of wormholing and uniform dissolution is observed for the higher injection rates. The modelling results are a first indication that statistical descriptions of transport and chemical heterogeneity can improve continuum scale reactive transport modelling.

No description available.

No description available.

A wide variety of "geological evidence supports the contention that the Troodos massif, Cyprus is a fragment of Mesozoic sea-floor created at a constructive plate margin. Here, the metamorphism and geochemistry of the dyke/pillow lava sequence at the top of the igreous succession are shown to be compatible with this proposal. The greater part of the sequence is basaltic and is divided by a metamorphic discontinuity near the top which sometimes coincides with an unconformity. This boundary separates two groups of lavas and their related dykes. Each unit has a characteristic metamorphic petrology. Metabasalts from the lower division, here termed the Axis Sequence, are comparable to those dredged from oceanic spreading axes, whereas the overlying rocks, the Upper Pillow Lavas, differ, and represent material erupted after the earlier metamorphic event. This group was subsequently metamorphosed in an environment with a lower the thermal gradient and its effects are not displayed by the Axis Sequence. Oxygen and strontium isotope data strongly suggest that the basaltic rocks of the Troodos massif have interacted with large volumes of seawater during the metamorphic events. A model for sub-sea-floor metamorphism at or near the Troodos spreading axes is erected. Most of the major elements are labile during metamorphic processes. It is only certain trace elements, notably Ti, Zr, Y, Cz and the rare earths which are unaffected by hydrothermal alteration and, as such, provide a clue to the compositions of the Troodos magmas. Even so, geochemical studies alone are incapable of defining the tectonic environment in which the Trooclos massif was generated, but coupled with other geological evidence, a petrogenetic model has been formulated in which the whole massif is seen to have developed at a decelerating spreading axis, probably in a marginal sea, back-arc environment.

Analytical techniques have been developed to measure the very small [230ThP32Th] atomic ratios (3-8x10-6) typical of basaltic lavas using a single focussing mass spectrometer. Compared to conventional alpha-counting methods, the technique presented typically gives a 2-5 fold improvement in reproducibility of 230 Th/232Th ratios, and furthermore uses -5x less sample, has a simpler chemical prepartion and a data aquisition time -100x shorter. The above technique was used in investigating a suite of historic (< 1000a) basanites from La Palma, Canaries. The lavas have undergone significant post melt segregration processes, involving residence in deep (>4kbar) magma chambers, that are inferred to persist for at least 30ka. The basanites show geochemical variations related to differences in the degree of partial melting, that are estimated to be between 0.3-2%. Rare earth element (REE) modelling suggests clinopyroxene, rather than garnet control during melting, contrary to expectations from recent geophysical models (McKenzie & O'Nions, in press). The La Palma mantle source is inferred to be LREE enriched, K& Rb depleted, and shows many incompatible element ratios characteristic of 'himu' basalts (Weaver 1991). In contrast, the 206pb/204pb ratios of the La Palma basanites (19.6±0.05) are lower than the isotopically defined'high p' basalts (Zindler & Hart 1986) which suggests that the La Palma source is geochemically similar, but younger than a typical 'high t' source. A suite of young (< 10,000a) high MgO tholeiites from Iceland show order of magnitude variations in highly incompatible element concentrations that correlate with FeO contents. Variations within these lavas is primarily attributable to sampling of instantaneous melts from different depths within a dynamic melting column. However, additional correlations of radiogenic isotope ratios with major and trace element contents highlights mixing of various plume melts with some 20% mid-ocean ridge basalt, derived from melting of upper mantle material entrained during plume upwelling.

The field relationships, primary and secondary petrography and chemical composition of granitic rocks (plagiogranites) and associated formations in five ophiolites are described. In addition, the occurrence of similar rocks in other ophiolites, some island arcs and in the ocean crust is reviewed. Plagiogranites in ophiolites can be distinguished from all other granitic rocks by their almost complete lack of potassium feldspar, low alumina content, high K/Rb ratio and their LREdepleted, flat or "dished" rare earth profiles and negative europium anomalies. The hypothesis that ophiolites represent oceanic lithosphere fragments is supported by the strong resemblance of some granitic rocks d~edged from the seafloor to those in ophiolites. Granitic rocks in ophiolites differentiate from subalkaline tholeiitic magmas at spreading axes in mid-ocean and in marginal ocean basins. These magmas evolved on a trend of ironenrichment unless FeTioxides appeared as fractionating phases, which seems to have followed saturation of the magma by seawater. The magma then became progressively enriched in silica and sodium, evolving by the removal of plagioclase, FeTioxides, apatite and zircon. However, potassium was partitioned into the magmatic volatile phase and so entered the open hydrothermal system at the spreading axis and was thereby not enriched in the plagiogranites. Plagiogranites in ophiolites are all deuterically altered to assemblages typical or upper greenschist or lower amphibolite racies metamorphism. Hydrothermal activity in the vicinity or each magma cell beneath the spreading axis ceased soon after the last of the silicate liquid froze and there was little repenetration of the ophiolite plutonic complex by hydrothermal fluids.

The St. Austell pluton is part of the large Hercynian batholith of south-west England. The pluton exhibits a complex sequence of mineralisation events, which occur as distinct hydrothermal vein generations associated with characteristic alterations of the host granites. Geological and petrographic observations indicate that the first mineralisation event following the consolidation of the granites consists of the intrusion of quartz porphyry (rhyolite) dykes and the formation of quartz-tourmaline veins. The latter are associated with the extensive greisenisation of the host granites. This study is concerned mainly with the subsequent evolution of the pluton, which is summarised in the following sequence of events: a. Quartz-fluorite veins, associated with hydrothermal alteration of the host topaz gran-ites and resulting in the formation of the "fluorite granite" petrographic type. b. Formation of quartz-haematite veins. The mineral assemblage of these veins consists of kaolin+illite+haematite+/-chlorite. The wall-rock granites of the quartz-haematite veins are altered to an assemblage consisting of kaolin+illite+haematite. c. Formation of kaolin+/-quartz veins, associated with the extensive kaolinisation of the host granites. The alteration assemblage consists of kaolin and smectite. Petrographic observations indicate that clay mineral authigenesis associated with the illitisation of the parent granites is controlled by differences in the precipitation kinetics of kaolin and illite. Similarly, the kaolinisation of the granites is mainly con-trolled by the slow precipitation kinetics of quartz, thus permitting SiO2 content of the fluids to exceed quartz saturation and allowing smectite to precipitate. Geochemical modelling of the kaolinisation allows the identification of the fluid/mineral equilibrium relations required for the formation of a kaolin+smectite mineral assemblage from the feldspar mineral assemblage of the parent granites. Paragenetic and fluid inclusion evidence suggest that successive mineralisation events occurred at progressively lower temperatures, culminating with the kaolinisation of the granites at relatively elevated temperatures of between 100 and 50°C. The nature of the hydrothermal fluids responsible for the formation of different alteration assem-blages is difficult to assess because of substantial uncertainties involved in the interpretation of the clay minerals' stable isotope compositions. Overall, the geological, petro-graphic, and fluid inclusion data favour the involvement of elevated temperature, moderately to highly saline fluids in both the kaolinisation and illitisation of the St. Austell granites. It is also considered that the kaolinisation of the granites did not take place due to the interaction of the parent granites with meteoric waters. The correlation of the geological and thermal history of the pluton during the Mesozoic suggests that the kao-linisation took place prior to the unroofing of the pluton and during a period of rapid uplift and cooling in the Middle Jurassic to Early Cretaceous. This uplift event is linked to the rifting associated with the opening of the Atlantic Ocean. The alteration of the parent granites is attributed to their interaction with either sedimentary brines expelled from the Plymouth Basin or with evolved (modified) meteoric waters.