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The behaviour of gas condensate flow in the porous media is distinctly different from that of gas-oil flow. The differences are attributed to the difference in fluid properties, phase behaviour, and condensation and vaporisation phenomena that distinguishes gas condensate fluids from the aforementioned fluid types. These differences manifest themselves into an important flow parameter that is typically known as relative permeability. Relative permeability is known to be related to the phase saturation, and the interfacial tension (EFT). Also, at high phase velocities, its reduction with increasing velocity, known as Forchheimer (turbulence) or inertia effect, is well documented. An unconventional behaviour of gas condensate fluids has been experimentally proven in Heriot-Watt laboratory and confirmed by other experimental studies performed elsewhere. These tests have shown that at intermediate velocities, before the inertia becomes significant, the gas and the condensate relative permeabilities are significantly improved by increase in velocity. This phenomenon is referred to as the rate-effect. None of the conventional relative permeability models include this experimentally proven favourable rate effect. In this work the flow of gas condensate fluids in porous media is modelled with emphasis on near wellbore conditions. Theoretical, empirical as well as simulational investigations are used to improve the present technology on the treatment of the flow of gas condensate in reservoirs. The use of X-ray or y-ray devices to monitor saturation profile during displacement experiments is investigated and the appropriate test conditions leading to reliable measured relative permeability data are determined. The regimes of the gas condensate flow at the core level, where the rate effect is evident, are investigated using the concept of Reynolds number. Then a mechanistic flow model, where the flow of gas condensate fluids is assumed to follow an annularmist flow criterion, is presented to capture the essence of the rate effect in perforations. The favourable EFT and rate effects are incorporated into the modelling of gas condensate relative permeability by correlating it with capillary number (I\Ic). Two forms of the correlation are presented. The impact of EFT and Ne together with the Forchheimer (inertia) on well deliverability is thoroughly investigated using the above correlation. The gas condensate relative permeability correlation is combined with the Forchheimer effect and used in a specially modified version of a commercial simulator, Eclipse 300V 98a development, to investigate the impact of IFT, Nc, and inertia on well productivity. The impact is found to accelerate production from gas condensate reservoirs. At practical production rates, the significance of the impact on phase recoveries cannot be ignored regardless of reservoir fluid richness or absolute permeability.

The work contained within this thesis is an assessment of the water uptake ability of various crude oils, and an investigation of the relationship between water uptake and the chemical composition of crude oils. U sing the Karl Fischer titration technique it was possible to achieve rapid analysis of the rate of change of the water content of prepared crude oil/water blends with various added water quantities. A set of procedures, called Crude Oil Water Uptake Analysis (COWUA), were established using this apparatus and applied to a group of crude oils, with varying maturity and extent of biodegradation, from two main oil producing provinces, the U.K. North Sea and Santa Maria Basin, California. Water determination from the top and bottom of crude oil/water blends, combined with visual inspection, was used to characterise the water uptake of crude oils by their water retentive (rate of sedimentation of water and/or emulsion droplets) and emulsion formationl/stabilisation (degree of oil/water separation) abilities. Initial results identified that both of these properties altered with the extent of biodegradation of the crude oil in question. Non-biodegraded crude oils exhibited "poor" water retention (rapid water or emulsion sedimentation) and formed stable water-in-oil emulsions, while degraded crude oils exhibited higher water retentive capability (slower sedimentation) yet possessed varied emulsification ability. Water retention was considered to be possibly due to either the physicochemical (viscosity, density etc.) or geochemical (crude oil compositional) properties of the crude oil. It was anticipated that the composition of crude oils, which exhibit "good" water retention would probably contain "emulsifiers", i.e., asphaltene and wax sols as well as oil-soluble surfactants, such as CO-C3 alkylphenols. These emulsifiers promote stable oil/water interfaces and produce good interaction between the immiscible phases, therefore slowing, or preventing, water and/or emulsion droplet growth. However, bulk chemical analysis showed that the effectiveness of asphaltene and wax emulsifiers decreased with increasing biodegradation and that NSO compounds exhibited no association with increasing water retention. Since no relationship between these crude oil geochemical compositions and increased water retention could be detected it is suggested that physicochemical properties of crude oil/water blends are probably responsible for the rate of sedimentation of the water content. The emulsion formation/stabilisation ability. of crude oils analysed varied. Bulk chemical analysis of the major crude oil chemical groups (aliphatic and aromatic hydrocarbons, resins and asphaltenes) showed that crude oils which formed stable water-in-oil emulsions either possessed a composition conducive to asphaltene and wax precipitation (as for the non-degraded North Sea crude oils) or possessed high NSO contents (as for both non-degraded and biodegraded Santa Maria Basin crude oils). However, where none of the above properties were exhibited, as for biodegraded North Sea crude oils, poor or no emulsion formation occurred. Detailed analysis of the CO-C3 alkylphenols found that their concentration was severely reduced in crude oils which were characterised by poor, or no, emulsification. Therefore, the reduction of oil-soluble surfactants (such as CO-C3 alkylphenols), as well as asphaltene and wax sols, is related to poor emulsion formation! stabilisation. The importance of emulsifiers was further outlined by analysis of the organic matter extracted from the crude oil/water interfacial film present in the emulsions. All the above emulsifiers were found to be preferentially enriched, indicating their involvement in the formation and stabilisation of water-in-oil emulsions. The effect of biodegradation upon water uptake was further investigated under controlled conditions, by the laboratory biodegradation of non-degraded and biodegraded North Sea crude oils. The subsequent emulsification of the non-degraded crude oil during biodegradation was not attributed to the presence of asphaltene and wax sols (biodegradation was considered to reduce the presence of these particles) but the result of significant surfactant generation. This phenomenon is associated with the rapid microbial degradation of the easily metabolisable components in the crude oil. Consequently, the observed lack of emulsification, for the previously biodegraded crude oil, was attributed to both the reduced presence of asphaltene and wax sols, as well as poor surfactant generation associated with slow degradation rates.

The probe permeameter is a recently developed device providing a small scale measurement of permeability. About 15,000 probe permeameter measurements were acquired for analysis during this study. These data were acquired by Statoil from cores in two North Sea wells. These cores are from the Middle Iurassic Rannoch Formation of the Brent Group. This reservoir unit was selected for this study because of its laminated nature and challenge to conventional description and simulation practice. All aspects of probe permearnetry are investigated in this study; the volume of investigation, the compatibility with measurements at larger scales, the measurement statistics. the optimum sample spacing. the relationship of the measurements to the geological description and the scale-up of data for two-phase numerical reservoir simulation. Careful analysis of probe and traditional plug data shows that the measurements are compatible. Systematic differences could be accounted for by different treatment effects of the material. The probe measurements show that the permeability distribution in the Rannoch Formation is closely related to the primary depositional structure of the sediment at a hierarchy of scales. This observation is used in combination with conventional simulation techniques to build a more geologically-realistic numerical model of the Rannoch Formation. The scale-up of the small scale measurements is achieved by generation of effective properties for geologically representative elements at various scales and is called the "geopseudo" method. The scale of the natural building blocks within the sediment were determined with the aid of an appropriate outcrop analogue. The model results compare favourably with field production data. This work demonstrates. for the first time. a systematic method for the scale-up of small scale petrophysical properties associated with lamination in sedimentary rocks. as measured by the probe permeameter. Laminated reservoirs are widely encountered and this work. therefore. makes a significant contribution to reservoir engineering practice.

This thesis reports an experimental and theoretical study on filtration properties of water based drilling fluids under dynamic and static conditions. The tested muds cover Freshwater/Gypsum/Lignosulphonate mud and SeawaterlKCLlPolymer mud, bariteweighted and unweighted. The effects of the solid concentration, pressure and shear rate on the filter cake characteristics and the erodability were investigated. For static filtration experiments, all tests were conducted for two hours and the spurt loss, the filter cake thickness, the ratio of wet to dry cake mass and the cumulative filtrate volume against time were measured. For dynamic filtration experiments, however, only the spurt loss and the cumulative filtrate volume against time were measured and all tests were conducted for at least 8 hours. A general filtration equation was developed based on the cake filtration theory prevailing in the chemical engineering industry and it was utilised to obtain the modified classic static filtration equation and the dynamic filtration equation. The modified classic static filtration equation was then employed to fit the static filtration experimental data and the average specific static cake resistance and the effective filter medium resistance were calculated. The dynamic filtration equation showed a substantial agreement with the dynamic filtration experimental data. Using the static filter cake properties such as the ratio of wet to dry cake mass (m), the average specific dynamic cake resistance, the effective filter medium resistance and the dynamic filter cake erodability were calculated. In the study of the relationship between the static filtration data and the dynamic filtration data, an attempt of predicting the dynamic filtration data from the static filtration experimental data was conducted. Also, an attempt was carried out to predict the static filtration data and the dynamic filtration data in a sequential process. The experimental data suggests that a substantial difference exists between the specific resistances of static and dynamic filter cakes. No apparent distinction was found, however, between spurt loss and effective filter medium resistance. The reodability of dynamically deposited mud cake for Seawater/KCL/Polymer mud was found to be three fold for Freshwater/Gypsum/Lignosulphonate.

The aim of this thesis is to achieve both a theoretical and empirical understanding of the local public inquiry system in the context of controversial North Sea oil and gas onshore developments. Part one develops a theoretical framework within which an analytical vocabulary is generated to describe the case studies in part two. it is argued that a concept of the political process which acknowledges that power and participation are inextricably bound together in public institutions is particularly appropriate for studying an institution such as a local public inquiry because it is both an instrument of government and a means of ensuring the fulfillment of 'natural justice' to individuals affected by planning and development issues. Part one develops this idea first through an historical examination of the concept of 'natural justice1 as a conflict between 'common-sense' notions of justice and 'formal' legal and administrative interpretations of what is 'fair', and then as a theoretical debate between the critical theory of Jurgen Habermas and the systems theory of Nicklas Luhmann. Part one concludes by arguing that the essence of the tension between Habermas and Luhmann articulates the tension between 'common-sense' notions of justice and 'formal legal' notions and that by using the vocabulary of 'classification and framing of knowledge' developed within educational sociology by Basil Bernstein, the Habermas-Luhmann debate can be condensed into an analytical tool enclosed within one theoretical structure. Power and participation as inter-connected forms of political engagement are expressed within the concept of the 'classification and framing of knowledge' as conflicting patterns in the relationship between knowledge and information and the institutional procedures that process that knowledge and information. Part two explicitly seeks to use the concept of the 'classification and framing' of knowledge to make visible the principles of power and social control that operate in large public inquiries. Attention is focused on local public inquiries into North Sea oil and gas onshore development; the case studies of the Cromarty Firth, Dunnet Bay and Drumbuie are described to illustrate how the 'classification and framing1 of knowledge operated in the Highlands in the 1970's. The case of Shell/Esso's petrochemical development in Fife is examined in detail to describe, first, the nature of participation and discontent within the local public inquiry system, and secondly, the relationship between the formation of local opposition in the form of an action group and the nature of the constraints imposed upon that organisation by the local public inquiry system. Part three attempts to clarify the theoretical and practical problems involved in reforming the local public inquiry system within the terms established by this thesis. The work of Jurgen Habermas is considered pivotal for developing a critical sociology of the public sphere. It is tentatively suggested that the new social movements rooted in ecology and opposition to nuclear power could be the bearers of an emerging critical theory of society and technology which might the grounding for a unified theory and practice which could lead to institutional change in society generally and in the planning sphere in particular.

In this thesis the taxation of North Sea oil is found to deter oilfield investment substantiaty - investment which it pursued would bring about Pareto benefits. Analysis of both the comparative static tax effects and the dynamics of taxation on oilfield development decisions reveals the nature of the deterrent, while a specially developed econometric model is used to quantify the impact of the tax structure and of tax changes on recoverable reserves. By detailing the mechanisms through which taxation distorts the allocation of investment resources away from North Sea developments, the thesis stresses that individual tax clauses tend not to perform the roles allotted to them and that tax changes alter the economics of oil projects in ways and in magnitudes that do not seem to be realised. Hence, not only is the nature of these effects misunderstood, but the extent oi these effects is much more damaging than commonly appreciated. These findings are reached by following the principles laid out in the early chapters which suggest that, if an improvement in the allocation of resources is to occur, laise beliets must be reclined. In particular, the inconsistencies between the targets and instruments of North Sea policy suggest there are false beliets about the need to stimulate development decisions and about the role of taxation - suggestions which are confirmed in the detailed research of the thesis. Having condemned existing North Sea oil tax policy, a practical, feasible and attainable alternative to the current tax system, that would not distort investment decisions so severely, is recommended.

During the tertiary stage of oil recovery, various chemicals and gases are injected into the reservoir. The success of these processes often depend on the ability of the injected chemicals/gases making contact with the residual hydrocarbon. The accessibility of the individual pore, where the hydrocarbon are trapped, to the injected fluid is therefore important. In many core flooding experiments which simulate such tertiary processes, the effluent profiles of the injected chemical often exhibit the capacitance effect of early breakthrough and long tails. These are mainly due to the fact that not all the pores are accessible to the displacing fluid. In this work, a mass transfer model, using physical meaningful parameters, has been set up to study the capacitance effect. The pore space are divided into a flowing fraction in which the bulk flow of the injected chemical takes place and a stagnant fraction where the chemical can only access by molecular diffusion. The significance and sensitivity of the five model parameters have been studied extensively using computer simulation. The extent of the mass transfer process is characterised by the different sets of family curves. A series of IPA/water miscible displacements using Clashach sandstone have been carried out to provide experimental data for model simulation. The assumption of the stagnant fraction in the form of dead end pores has been supported by the results of hexane/toluene displacements at connate water saturation. Some problems of history matching the experimental results by model simulation have been highlighted. This is mainly caused by the difficulty of establishing an analytical solution for the model equation and the need to optimise simultaneously the five model parameters. Various approach to overcome these problems have been successfully demonstrated in this work and further possible improvement has been identified. The source of numerical dispersion and the different corrective schemes proposed in various papers have been summarised and compared. One of these, the method of lines (MOL) has been used successfully in this work to minimise numerical dispersion. The understanding of the non-equilibrium capacitance effect in porous media is essential in order to interpret the production data and, in particular, laboratory core flooding results correctly. It is also important, for the mathematical model, to use parameters which are physically meaningful to the process itself. The work carried out in this research has provided a detailed study on this subject.