The impact of brine composition on rock wettability and oil recovery in carbonates has been an area of active research in recent years. Many studies have reported contradictory results and the underling mechanism(s) are actively debated. The zeta potential, which is a measure of the electrical charge at the mineral surface, is highly variable in carbonates, depending on the ionic composition of the pore water. The zeta potential controls the magnitude and polarity of the electrostatic interactions between the mineral surface and polar species in the brine and oil; it also controls the magnitude and polarity of the streaming potential, an electrical potential which arises in response to pressure gradients across saturated rocks. Here we report the use of streaming potential measurements to determine key controls on zeta potential at mineral-brine and oil-brine interfaces, and characterise wettability and optimise injection brine composition during controlled salinity waterflooding in carbonates at reservoir conditions of salinity and temperature. The zeta potential is controlled by the concentration-dependent adsorption of the lattice ions Ca2+, Mg2+ and CO32- within the Stern layer. A Nernstian relationship between zeta potential and pCa or pMg (where p represents the negative logarithm of concentration in M; 1 M = 1 mol L-1) is observed over the range of typical natural brines. Addition of SO42- can affect zeta potential by moderating Ca2+ in solution. The temperature dependence of the zeta potential can be correlated with the temperature dependence of pCa and shows a Nernstian linear relationship. The zeta potential in intact carbonate samples decreases with temperature at low ionic strength and independent of temperature at high ionic strength irrespective of brine composition. Thus, for a given carbonate type, zeta potential measurements in natural brines (e.g. saline aquifers, formation waters or seawater; ionic strength ≥ 0.5M) at laboratory conditions may be applied in situ. The zeta potential at both the mineral-water and oil-water interfaces must be determined when characterising wettability and designing the optimum brine composition for controlled salinity waterflooding in carbonates. The experimental method presented here allows this to be done using intact core samples saturated with the crude oil and brine of interest. We find a monotonic relationship between zeta potential and wettability expressed in terms of the Amott water index (Iw). Thus, measurements of streaming potential can be used to characterise wettability more quickly and cheaply than existing laboratory methods. Results reported here demonstrate that the oil-water interface can be positively charged at the high pH and ionic strength relevant to the formation brines found in many carbonate reservoirs. It is usually assumed that the oil-brine interface is negatively charged. Improved recovery during controlled salinity waterflooding in carbonates is observed if the change in brine composition yields a zeta potential at each interface that has the same polarity, such that a repulsive electrostatic force acts between the interfaces and stabilizes a water film on the mineral surface. These results have broad application and significance in allowing oil companies to design water injection strategies that yield improved oil recovery from carbonate reservoirs.

The pre-Himalayan magmatic events along the northern margin of Indian plate in north-western Pakistan have been investigated and correlated with analogous magmatism in other Himalayan and northern Gondwana regions. The samples from Utla and Mansehra regions of NW Pakistan are dominantly megacrystic two mica granites, strongly peraluminous (A/CNK > 1.1) and intruded by aplite dykes and quartz-rich veins. The high precision zircon U-Pb ages (471-479 Ma) show their emplacement in early Paleozoic. These granites are enriched in light rare-earth elements (LREEs) and show similar chondrite normalized REE patterns with negative Eu anomalies (Eu/Eu* = 0.07–0.73). The geochemical signature and REE based modelling indicate that the granites are derived mainly from the partial melting of pelitic source followed by the evolution of melt via fractional crystallization resulting in the formation of aplites. Tourmaline occurrences in distinct modes show post-magmatic alteration of these granites triggered by hydrothermal fluids from different sources. Enrichment of Sn in certain alteration zones and trace elements ratios suggests a strong mineralization potential for these granites. The analogous composition, source rock characteristics and geochronology represent their regional association with other Cambro-Ordovician granitoids from northern Gondwana. Due to these similarities, an early Paleozoic orogenic event has been anticipated for these granitoids initiated due to subduction of Proto-Tethys oceanic lithosphere beneath the northern Gondwana supercontinent. Dykes of basic composition that intrude these granites and other lithologies are divided into dolerites and amphibolites on the basis of their distinct mineralogical and geochemical composition. Major elements composition suggests alkaline to sub alkaline character of both dykes with intraplate tectonic setting, however, amphibolites (>3%) are markedly enriched in TiO2 relative to dolerites (<3%). Trace element ratios designates the origination of dolerites from subcontinental lithosphere with significant crustal contamination. They show analogous geochemical character to Panjal traps which represent a regional scale rift related basic magmatism in Himalayan terrane during Permian. The geochemical signature of amphibolites, however, show similarities to high-Ti Qiangtang dykes which originates from asthenospheric source via deep mantle plume. The sporadic distribution of both dykes in similar aged host rocks represent their evolution from distinct sources in separate but synchronous magmatic pulses during extensional tectonism related to separation of Cimmeria from Gondwana. Granites with distinct petrographic features have been tested to examine the influence of textural characteristics on the variation of their respective strength. Comparison of petrographic observations before and after the strength tests and the relationship of fracture propagation with mineral boundaries specifies vital impact of textural variation in evaluating the mechanical behaviour of granites. The important textural features include average grain size of rock, grain boundary recrystallization, maximum grain size of major rock forming minerals, mean grain size of cleaved minerals, mineral exsolution and variation of grain size within a rock. The petrographic observations, however, are more effective to describe the strength variation of granites having analogous weathering grade as change in degree of weathering has a dominant effect on rock mechanics.

This work was carried out within the Qatar Carbonates and Carbon Storage Research Centre to improve the characterisation of carbonate reservoirs. 3D images obtained using X-ray micro-tomography were used to characterise heterogeneity in surface area in one sandstone and five carbonate rocks. Surface area measured from X-ray imagery were 1 to 2 orders of magnitude lower than nitrogen BET measurements. Roughness factor, i.e. the ratio of BET surface area to X-ray based surface area, was correlated to the presence of clay or microporosity. Comparing statistical distributions of surface area to those in published modelling studies showed that the common practice of leaving surface area and pore volume uncorrelated in a pore led to unrealistic combinations of surface area and pore volume. In Berea sandstone, constraining ratios of surface area to pore volume to a range of values between that of quartz-lined and five times that of clay-lined spheres appeared sufficient. Statistical analysis suggest that at 600 micrometre, the observations do not yet form a representative elementary volume. The development of dual-energy CT for phase identification is presented. Kaolinite, plagioclase, biotite, quartz, orthoclase, albite, dolomite, calcite, pyrite, magnetite, and hematite were scanned. The pairs: plagioclase-orthoclase, albite-quartz, biotite-orthoclase, and hematite-magnetite were not distinguished. Discrimination was possible for all other combinations. In Berea sandstone, kaolinite-smectite, quartz-albite, alkali feldspar-plagioclase, and pyrite-rutile were identified separately. Dual-energy CT has better contrast or capacity for larger samples than single-energy CT. Finally, an adsorption isotherm was measured from batch experiments with quartz and aqueous caesium chloride. 0.755 M of caesium remained in solution while 0.995 mole of caesium was adsorbed per square metre of quartz. Adsorption was expected to increase average attenuation seven-fold and contribute to 86% of the average attenuation in the image. CT images were collected of an equivalent column experiment with quartz powder and aqueous caesium chloride. However, adsorbed caesium was measured to contribute less than 1% of the average attenuation. This work has provided new capabilities to characterise pore-scale mineral and surface area heterogeneity and improve our understanding of CO2 storage in carbonates.

Headwater systems often comprise alluvial rivers interrupted by reaches with partly or entirely rock beds, indicate a local change in bedload conveyance relative to sediment supply. Detailed knowledge of sediment dynamics in bedrock-alluvial systems is crucial for a better understanding of bedrock incision and sediment delivery downstream, but field evidence is lacking. This thesis reports a field investigation in this topic. Coarse bedload transport was studied in alluvial, semi-alluvial and bare rock segments of Trout Beck in North England by monitoring two sets of 270 magnet-tagged pebbles over a period of nineteen months. At-a-station hydraulic geometry, flow resistance and shear stress were estimated using stage recorders, water surface profiles and salt-wave measurements in five short sub-reaches. Thresholds of motion were investigated using tracer-pebble data and bedload impact counts. Tracers seeded in the upstream alluvial channel moved more slowly. Tracers seeded in a bare rock gorge dispersed quickly at first but accumulated in a coarse-sediment zone at the start of the next partial cover. Bedload transport was size selective over alluvial or semi-alluvial segments but not over bare rock. Flow resistance, as quantified by Manning’s n or Darcy-Weisbach f, varies considerably with both discharge and bed character. The estimated bedload conveyance is highest in reaches with entirely or mainly rock bed, and lowest in alluvial and boulder-rich segments. The boulder-rich segment has high shear stress, but presumably its threshold stress is also high due to form drag from boulders, as evidenced by very high values of n and f. No standard resistance law describes flow in Trout Beck accurately from measured bed D84. This study demonstrates how bedrock reaches control sediment processes and how they are different from alluvial reaches.

This thesis is concerned with the inversion of lattice pore-network model parameters of carbonate rocks using only the capillary pressure, and then the use of the inverted parameters to predict the water-flooding relative permeabilities of the carbonate rocks. Background: There has been a tendency to claim that pore-network modelling using three-dimensional micro-computed tomography or 3D mathematically created images can predict imbibition relative permeabilities for wettabilities other than strongly water/oil-wetting. This is based on the flexibility for matching data, which is a weakness of pore-network modelling. The method proposed in this thesis is important because a large percentage of the porosity in carbonates is microporosity. Conclusions: We applied stochastic inversion of lattice pore-network model parameters using Hamiltonian Dynamics (Hamiltonian Monte Carlo) to three carbonate rock samples and we predicted water-flooding relative permeabilities with good accuracy by using as constraint only routinely obtained data, such as mercury intrusion capillary pressure (MICP) and oil/water capillary pressure. We found that there is a strong correlation between the amount of microporosity and the volume exponent parameter. This suggests that when microporosity is ignored, the volume exponent will tend to be systematically strongly underestimated. HMC found large variability in wettability that causes mid-sized pores to be invaded at the same level of pressure as larger pores. The coexistence of these events reduces the tendency for preferential flow through large pores, resulting in more uniform flow at the pore scale compared with the case in which flow is restricted only to large pores. Mid-sized pores have an important effect on the connectivity because they could have higher contact angles than larger pores. Therefore, they do not spontaneously imbibe and shield larger pores, improving water-flooding displacement. The wettability of micropores could better explain the gentle curvature of the imbibition water relative permeability compared with the generally assumed mixed-wet large wettability model. The importance of the maximum and minimum observed capillary pressure is directly connected to accounting for the full pore-size distribution. Thus, the common assumption that microporosity can be ignored is unsatisfactory. The ranges of advancing contact angles obtained from the HMC inversion were wider than the ranges of apparent advancing contact angles obtained with analytical determinations in previous studies, and in one case our results were contradictory to the analytical determination. It follows that variability in advancing and receding contact angles is not reflected in the apparent contact angle data outside porous media. Apparent contact angle data outside porous media cannot completely characterise the wettability in porenetwork models because the data does not capture the contact angle variability in porous media. The existence of wetting films depends on the maximum capillary pressure during drainage, and thus wettability alteration during ageing. Our results suggest that matching both connate water at the maximum drainage capillary pressure before ageing and matching residual oil at the minimum imbibition capillary pressure leads to better estimation of the advancing and receding variability in the contact angles.

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This research has developed novel techniques to reconstruct a variety of aeolian dune architectures using subsurface datasets, supplemented by outcrop studies and data from analogous modern aeolian systems. These methods demonstrate the ability to reconstruct larger-scale aeolian architectural elements in the subsurface, aeolian bedform geometries, regional reservoir stratigraphic heterogeneity, and original bedform morphology and style of migration. Once the original bedform morphology and style of migration has been determined, three-dimensional forward stratigraphic models have been developed which enable the reconstruction of the three-dimensional spatial arrangements of sets, internal facies arrangements, quantitative estimates of three-dimensional sand-body geometries, and likely geometry and degree of interconnectivity of net reservoir facies. This research has additionally investigated predictable responses in well log data (e.g. dipmeter data) for a variety of aeolian bedform types to determine original bedform morphology. The effect that original bedform morphology has on the overall reservoir quality of a volume through the interpretation of facies distributions, net reservoir calculations and connectivity has also been explored.

A first-principle modelling framework for thermo-hydro-mechanical-chemical processes in fractured rock is developed. The key characteristics of such rocks are incorporated by direct representation: the power law nature of fracture size distribution, the fractal nature of rock surfaces, the scale dependence of discrete contact between these, and the mechanically induced fluid-flow anisotropy. It is shown that hydro-mechanical modelling in fractured rock can be reduced to a single free parameter, the friction coefficient. Properties of fractured rock, such as transmissivity, stiffness and permeability, emerge as direct results of physical processes, and need not be complemented by empirical relationships or distribution functions. Results reproduce the field observation that critically-oriented fractures are likely hydraulic conduits; while the established reasoning of shear activation and associated fracture dilation for this fact is confirmed, it is also shown, for the first time, that chemically-mediated processes have the potential to contribute to this effect. Compaction mechanisms of pressure solution and precipitation act preferably on fractures with stress ratios far from Coulomb failure, which increases the relative contribution of near-critical fractures. New insights also emerge as to the likely orientation of the maximum permeability of a fractured rock mass. Due to shear-induced anisotropy of fracture transmissivity, the preferential flow direction tends to be aligned with the orientation of the intermediate stress. The capability to accurately determine the upscaled permeability tensor is facilitated by a novel algorithm that is independent of geometry and reference system, and accounts for locally anisotropic matrix permeability and fracture transmissivity. The developed framework presents a path forward in fractured rock modelling. It accounts for state of the art knowledge of the internal processes of fractured rock across multiple scales, and perhaps aids to overcome the necessity for using isotropic effective properties that is prevalent in many applications.