The injection of CO2 into the reservoir acidifies the brine, which in turn drives mineral dissolution and precipitation processes. This thesis explores how far geochemical modelling can be applied to evaluate the CO2-brine-rock interactions during CO2 storage in North Sea saline formations. First, modelling requirements and the capabilities and limitations of the numerical codes used in this study (PHREEQC, GEM, TOUGHREACT and MoReS) were identified. Solubility of CO2 in brine by different models at conditions relevant to CO2 storage was compared. Batch modelling of three sandstone core samples from target CO2 storage formations was performed to compare the numerical codes and assess mineral trapping capacity of the formations. Finally, reactive transport modelling of Rannoch formation at reservoir scale was studied. The simulation results of GEM and MoReS were compared. It was shown that current codes can model geochemical reactions with acceptable simplifications and the choice of simulator is not critical for the model predictions. It was demonstrated how thermodynamic data and activity models can affect the modelling results. It was also found that the models are sensitive to relative mineral composition, grid discretization, permeability models, and kinetic parameters. Mineral trapping is comparable to solubility trapping in Rannoch formation.

In the search for new conventional oil and gas reserves, operators are moving into more challenging reservoirs. The move of the oil and gas industry into increasingly deeper and colder locations and/or production from mature reservoirs, in which water cut can be relatively high, has faced the industry with a major challenge, because the traditional hydrate prevention methods are very expensive (i.e., high CAPEX and/or OPEX) and even, in some cases, unfeasible. In this context, hydrate management may be more economical than hydrate avoidance. Forming dispersed hydrate particles using Anti-agglomerants (AAs) is currently an attractive option for overcoming hydrate blockage problems, especially for long tieback and high subcooling systems. This study mainly focuses on the rheological behaviour of hydrate slurry in high water-cut systems (from 60 to 80%), as these are probably the most difficult conditions for managing flow assurance issues using conventional techniques. To engineer a controlled formation of slurry flow made up of hydrate particles in high water cut systems, it is critical that the flow characteristics of water-oil emulsions and the hydrate slurries are well understood. In high water cut systems, by converting a certain amount of water phase into hydrate particles, the behaviour of hydrate slurry will be strongly dependent on the water-oil emulsion which acts as a carrier fluid to the hydrate particles. In this case, the behaviour of water-oil emulsions can depend on many parameters, such as the presence of natural surfactants, AAs, salt and even hydrate particles, might affect the morphology of the emulsions. So far, however, in terms of hydrate slurries, there has been very little research on the morphology of water-oil emulsions in the presence of AAs and hydrate particles. This work is initially focused on the effect of these parameters on the stability of water-in-oil (W/O) emulsions, oil-in-water (O/W) emulsions and phase inversion from W/O to O/W and vice versa. The rheological study of hydrate slurries is a difficult subject and to date there has been little study on this issue. Most of these studies have focused on low water cut systems and there is a lack of data specifically relating to hydrate slurries in high water cut systems. In this research work, which concentrates on the rheological behaviour of hydrate slurries in iii high water cut systems, the agglomeration of hydrate particles has been shown to be responsible for the rheological behaviour of water/oil/hydrate mixtures through viscosity measurements from an in-house high pressure Helical Tube Impeller (HTI) viscometer and pressure drop measurements from a pilot-scale flow loop. The effect of oil composition, AA concentration, water cut, shear rate and salt concentration has been investigated on the rheological behaviour of hydrate slurries in high water cut systems. Existing models to predict viscosity of hydrate slurry do not consider the effect of water-oil emulsion, which acts as a carrier fluid for transporting hydrate particles. It will lead to deviations between model and experimental data specifically relating to hydrate slurry in high water cut systems. In this study a model has been developed to predict the viscosity of water-oil emulsion in the presence of hydrate particles in high water cut systems using the concept of a bimodal mixture. In the model, water-oil emulsion and hydrate aggregates in the liquid continuous phase are treated separately as unimodal models. A new modification of Mills’ (1985) equation has been applied to describe the viscosity of unimodal hydrate suspension. The model has been validated using experimental data acquired by the HTI viscometer for water/oil/hydrate mixtures in the presence of different AA concentrations and different oil compositions. The predictions of the proposed model are in good agreement with experimental data for both experiments performed with oil-in-water and water-in-oil emulsions

Cost estimating and cost modelling for building projects have attracted the attention of many scholars. Previous research has laid emphasis on the product physical variables and did not explicitly include the economic variables. This study aims at investigating the impact of the performance of the economy on the cost of building projects by explicitly considering the relevant economic indicators in the cost estimating process. The unique attributes of the National Project for Building Schools in Egypt that is running since 1992, provided the opportunity to focus the light on the economic variables due to the standard design applied to thousands of school buildings. The study started by reviewing the current practice in cost estimating for building projects in Egypt seeking to identify the influential cost factors and to further investigate the level of awareness of the impact of the economic changes on the cost of buildings as perceived by the experts. In addition, the study aimed at developing an explanatory cost model illustrating the relationship between the relevant economic indicators and the cost of school buildings in order to quantify the impact of the economic changes on the costing of buildings. This research adopted a mixed methodology in a triangulation approach that was conducted in two stages. A set of 18 interviews with experts from the industry was followed by a survey covering a sample of 400 schools. The results indicated that the quantity surveyor’s method is the prevailing cost estimating technique in Egypt. Practitioners in general, showed a blurred understanding of the fundamentals of economic and did not explicitly consider the economic indicators in the cost estimates for building projects. The cost modelling of the survey data adopted a multiple regression technique and factor analysis. Two sets of Cost Models including 6 economic indicators as independent variables, besides other product variables, were developed. The results indicated that the economic indicators were significant cost variables. Hence, the impact of the economic changes on the cost estimates of buildings can be quantified. The produced models indicated that the cost of school buildings, expressed in real terms, tend to increase during periods of economic recession. The produced model is useful to cost estimators working for government clients as well as contractors, given the rising application of standard design in various sectors within the construction industry in Egypt. Further work is required to gauge this impact across various sectors of the construction industry

Shales in the reservoir and the surrounding rocks are often regarded as mechanically active for stress deformation and inactive barriers for fluid flow transportation. In clastic reservoirs experiencing pressure depletion due to production, the sands naturally compact to some degree. Consequently, the much lower permeability intra-reservoir and non-reservoir shales may experience mechanical tension. It is well documented that the dilation in the overburden and underburden shales leads to a detectable time shift in the seismic (Hatchell et al., 2003; Tura et al., 2005; Sayers, 2010). Less well know is that the combined effect of stress deformations and pressure diffusion in the non-reservoir and intra-reservoir shales may alter the predicted effective seismic response of the reservoir interval and the surrounding rocks. In this thesis, the combined effect of geomechanics and pressure diffusion process in the reservoir and non-reservoir shales is examined. The integration of these coupled mechanisms into forward seismic modelling is performed to assess the 4D seismic implications. For this, both; synthetic and field data are used in this thesis. It is commonplace to regard shales as barriers in the simulation of reservoir fluid flow induced by hydrocarbon production. Whilst this appears correct for fluid exchange, this is not the case for the fluid pressure component of this process. Based on this work, I observe that pore pressure reduction due to reservoir depletion can propagate significant distances into the intra-reservoir and non-reservoir shale over the production time scale. This diffusion process opposes the geomechanical effects. Numerical computation for a range of shale permeabilities suggests that intra- reservoir shales of 1m to 10m thickness should be considered as active when quantitatively assessing the 4D seismic signature with frequent acquisitions of 3 to 12 months. The critical set of parameters required to carry out accurate calibration of these predictions is not yet fully available from published literature. Also it is observed that pressure depletion in the reservoir can ‘propagate’ distances of as much as 50m into the shale over/under burden during the production time scale. Consequently this could leads to different polarity of time shift above and below the reservoir. In this thesis, I consider two field case studies. In the first case study I focus on the Schiehallion field. Here, the coupled mechanisms of geomechanics and pressure diffusion is integrated into the forward modelling of time lapse seismic. It is found that the polarity of the P-wave acoustic impedance changes and the corresponding synthetic 4D amplitude changes obtained from the coupled mechanisms are different from those modeled using geomechanics alone. Remarkably the synthetic 4D seismic amplitude generated using the coupled mechanisms is in agreement with the observed 4D amplitude. The second field case study is the HPHT Erskine field from the UK central North Sea. Here, 4D seismic data have been used to investigate the combined effects of geomechanics and pressure diffusion on the intrareservoir and non-reservoir shales. Modelling of synthetic seismic time shifts capturing these effects allow a quantitative evaluation of the observed 4D seismic time shifts. In particular, the comparison between synthetics and observations helps to calibrate the range of permeability for the Heather formation and the Erskine shale units. This calibration gives rise to a model which should more reliably predict the pore pressure and stress tensor changes, allowing more confidence in selecting safe well paths, mud weights, and casing schemes. For this particular case, the results suggest that the Heather formation undergoes pressure diffusion and consequently the trapping mechanism at the Heather shale is highly uncertain. The Erskine shale, however acts as an effective pressure barrier, and hence it is overpressured relative to the surrounding formations and could be a high-risk formation for future drilling programs. The results of this work strongly indicate that the understanding of shale geomechanics and pressure diffusion is essential to adequately understand the elastic wave stress sensitivity of the reservoir and the surrounding rocks. Based on the field case studies, the observed timelapse seismic data are consistent with the combined effects of shale geomechanics and pressure diffusion, and are preferable to taking into account only the geomechanical effects. In addition to the above, the results suggest that the need for shale properties should be recognized and measurement become more common practice in order to calibrate the predictions made in this study.

No description available.

Efficient and profitable oil production is subject to make reliable predictions about reservoir performance. However, restricted knowledge about reservoir distributed properties and reservoir structure calls for History Matching in which the reservoir model is calibrated to emulate the field observed history. Such an inverse problem yields multiple history-matched models which might result in different predictions of reservoir performance. Uncertainty Quantification restricts the raised model uncertainties and boosts the model reliability for the forecasts of future reservoir behaviour. Conventional approaches of Uncertainty Quantification ignore large scale uncertainties related to reservoir structure, while structural uncertainties can influence the reservoir forecasts more intensely compared with petrophysical uncertainty. What makes the quantification of structural uncertainty impracticable is the need for global regridding at each step of History Matching process. To resolve this obstacle, we develop an efficient methodology based on Cartesian Cut Cell Method which decouples the model from its representation onto the grid and allows uncertain structures to be varied as a part of History Matching process. Reduced numerical accuracy due to cell degeneracies in the vicinity of geological structures is adequately compensated with an enhanced scheme of class Locally Conservative Flux Continuous Methods (Extended Enriched Multipoint Flux Approximation Method abbreviated to extended EMPFA). The robustness and consistency of proposed Hybrid Cartesian Cut Cell/extended EMPFA approach are demonstrated in terms of true representation of geological structures influence on flow behaviour. In this research, the general framework of Uncertainty Quantification is extended and well-equipped by proposed approach to tackle uncertainties of different structures such as reservoir horizons, bedding layers, faults and pinchouts. Significant improvements in the quality of reservoir recovery forecasts and reservoir volume estimation are presented for synthetic models of uncertain structures. Also this thesis provides a comparative study of structural uncertainty influence on reservoir forecasts among various geological structures.

This research applies both quantitative and qualitative methods to investigate the sustainable development (SD) benefits of the Clean Development Mechanism (CDM) projects. The results of cluster analysis confirm that the carbon market is separated into two sub-markets: a premium market; and a normal market or may be defined as “One CER Two Markets”. A willingness to pay study revealed that buyers are willing to pay a price premium of €1.12 per tonne of CO2e for carbon credits with high quality sustainability benefits. 56.4% of the buyers are willing to pay a price premium for Gold Standard carbon credits. The probability of the willingness to pay a price premium is affected positively by the four factors: (i) Buyer’s perception of the SD benefits; (ii) Buyer’s perception of return on investment (ROI); (iii) An involvement in CDM sustainability label; and (iv) Buyer’s attitude towards an importance of CDM sustainability labels. The CDM’s contribution to SD is explored in the context of a biomass (rice husk) case study conducted in Thailand. The results of Analytic Hierarchy Process (AHP) show that stakeholders ranked ‘increasing the usage of renewable energy’ as the most important SD benefit, whereas they considered air pollution problems associated with dust as the most significant social cost. Qualitative results, suggest that rice husk CDM projects contribute significantly to SD in terms of employment generation, an increase in usage of renewable energy, and transfer of knowledge. However, rice husk biomass projects create a potential negative impact on air quality. Finally, these results indicate that the results of a sustainability assessment conducted by host countries may be inadequate, suggesting an inability of host countries to ensure the sustainability of CDM projects. In order to ensure the environmental sustainability of CDM projects, stakeholders suggest that Thailand should cancel an Environmental Impact Assessment (EIA) exemption for CDM projects with an installed capacity below 10 MW and apply it to all CDM projects.

Production of oil and gas from hydrocarbon reservoirs results in reduction in reservoir pressure and changes in the fluid composition and saturations. Enhanced oil recovery methods such as Gas Injection, Water Flooding, CO2 Injection, in-situ Combustion, Water Alternative Gas injection (WAG) and so on have similar effects. Variation of these properties can lead to changes in the velocity of sound in subsurface layers. On the other hand, any change in temperature, pressure, composition and density of pore fluids has strong influence on the seismic elastic properties. Elastic properties of fluids are usually simplified in geophysics. All existing software employs empirical relations to calculate seismic wave velocities in reservoir fluids. In this study, thermodynamic properties have been considered as first and second order derivative properties of the thermodynamic potentials. For this purpose, a statistical thermodynamic approach, with the Statistical Associated Fluid Theory – Boublik - Alder – Chen – Kreglewski has been used and developed further for mixtures and real oils by proposing new mixing rules, tuning binary interaction parameters, and utilizing the properties of single carbon numbers. In addition, a large number of experimental data on pure, binary and multi-component systems have been generated in this work. The predictions of the model developed in this work have been validated against the experimental data generated in this work and those reported in the literature. The predictions were found to be in very good agreement with independent experimental data.

Prevention of gas hydrate blockages is a major challenge posed to the petroleum industry because uncontrolled formation of hydrate may result in plugging of transport pipelines, causing considerable production loss and personnel safety hazard. Injection of hydrate inhibitors is the most common option to prevent hydrate formation. In current industrial practice the dosage of hydrate inhibitor is estimated and injected upstream without much downstream measurements. Therefore, hydrate blockages are still encountered in the oil and gas industry due to lack of any hydrate monitoring measures against unexpected changes. In this thesis, novel techniques have been developed for monitoring hydrate inhibition and detecting early signs of hydrate formation based on downstream sample analysis and online measurements. The main achievements of this study can be categorised as follow: 1. Hydrate Inhibition Monitoring Techniques: Three techniques, i.e. conductivity-velocity (C-V) technique, water activity technique and water content technique, have been developed for determining optimising inhibitor injection rates 2. Initial Hydrate Formation Detection Techniques: The main objective of detecting early signs of hydrate formation is to give the operators adequate time to prevent hydrate formation and start remediation actions. Two techniques including the onset of hydrate formation and compositional change have been developed for detecting initial hydrate formation 3. Development of prototypes: Following the above fundamental studies, prototypes of the CV and water activity methods have been developed The development of hydrate inhibition monitoring and early hydrate formation detection techniques opens a novel flow assurance approach for the oil and gas industry. The developed hydrate monitoring techniques like the C-V technique, water activity and content techniques can be used to optimise hydrate inhibitor injection. In the near future, further development of the investigated early hydrate formation detection techniques like gas compositional change technique could provide an effective measure to minimise the risk of hydrate blockage.

Understanding what controls the enhanced oil recovery during waterflooding of carbonate rocks is essential as the majority of the world’s remaining hydrocarbon reserves are contained in carbonate rocks. To further this understanding, in this thesis we develop a pore-scale simulator that allows us to look at the fundamental physics of fluid flow and reactive solute transport within the porous media. The simulator is based on the combined finite element – finite volume method, it incorporates efficient discretization schemes and can hence be applied to porous domains with hundreds of pores. Our simulator includes the rule-based method of accounting for the presence of the second immiscibly trapped fluid phase. Provided that we know what chemical conditions initiate enhanced oil recovery, our simulator allows us to analyse whether these conditions occur, where they occur and how they are influenced by the flow of the aqueous phase at the pore scale. To establish the nature of chemical interactions between the injected brines and the carbonate rocks, we analyze the available experimental data on the single-phase coreflooding of carbonate rocks. We then build a continuum scale simulation that incorporates various chemical reactions, such as ions adsorption and mineral dissolution and precipitation. We match the output of the continuum scale model with the experimental data to identify what chemical interactions the ions dissolved in seawater are involved in.