The work described in this thesis was undertaken to support the development and application of Shell Global Solutions LightTouch oil and gas exploration technique, which uses inverse dispersion modelling to predict a plume's source location from atmospheric concentration measurements. The overall aim was to develop a better understanding of dispersion issues relevant to the interpretation of measurements from fixed and mobile sensors. This translated into understanding how dispersion models assisted this activity and, where appropriate, developing modelling capability. A LightTouch field trial, conducted in the Algerian Sahara is analysed. Concentration measurements, collected using a survey aircraft, revealed a complex, non-Gaussian plume structure. It is shown by the application of the Atmospheric Dispersion Modelling System (ADMS) that the data demonstrate an episodic release in the presence of an existing methane background. An accurate reconstruction of the observed behaviour is demonstrated.

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Heavy oil contained in naturally fractured reservoirs is becoming an important resource as conventional oil reserves are depleted. However, maximizing recovery from such reservoirs is problematic due to the low flow rate of oil and the poor understanding of recovery mechanisms. One EOR method that is of particular interest is Thermally Assisted Gas-Oil Gravity Drainage (TA-GOGD). In this process, steam is injected into the reservoir. This heats the rock matrix blocks through the higher penneability fracture network and improves oil recovery principally by reducing the oil viscosity and thus increasing the rate of gravity drainage through the matrix. The work presented in this thesis aims to investigate and understand the mechanisms controlling the rate of gravity drainage during TA-GOGD and determine the key reservoir parameters that control recovery. This was achieved by studying the time scales for heating the matrix blocks by steam and gas oil gravity drainage as a function of reservoir and fluid properties using analytical formulae and detailed reservoir simulations. During the heating investigation, a simple formula for calculating the critical steam rate in the fractures is derived analytically. The formula shows that there is a critical steam injection rate for TA-GOGD in fractured reservoirs. If the injection rate is below this critical rate, the time to heat the matrix will increase and oil recovery increases with increasing injection rate. If the steam injection rate is greater than the critical rate then there is no significant increase in oil recovery with rate. The oil recovery mechanisms of TA -GOGD were also investigated numerically. The study involved the investigations of individual and collective impacts of the mechanisms of solution gas drive, C02 generation, steam distillation, connate water evaporation and gravity drainage, on the oil recovery for reservoir containing heavy oil using real field data and parameters. It was found that CO2 generation, water imbibition and oil expansion contribute more to oil recovery in the early times of oil production whereas distillation, thermal gas drive, viscosity reduction and gravity drainage mechanisms contribute more in the late times.

Asphaltenes represent some of the largest and most polar molecules found in crude oils and are known to be surface active. Whilst one of the least valuable fractions of a crude oil, asphaltenes have never-the-less received a great deal of scientific attention due to the risks their behaviour poses to oil recovery, transportation and processing. Subtle changes in the chemistry of crude oils or physical conditions can cause changes in the aggregation state of asphaltenes, which may precipitate out of solution blocking pores in reservoir rocks, altering surface wettability or fouling pipelines and refinery equipment. The complex and polydispersed nature of asphaltenes and their propensity to aggregate in solution makes them very difficult to characterise and despite many studies a definitive picture of their chemistry, molecular weight and aggregation behaviour has not been found. The aggregation state, geometry and molecular weight of petroleum asphaltenes are investigated using a Langmuir trough in Chapter 2. A novel mathematical model based upon the van der Waals modified equation of state was used to predict aggregation numbers and limiting areas of asphaltene aggregates at the air water interface. Non-ionic surfactants are widely used in many industries including many stages of oil recovery and production. The solubility and aggregation behaviour of a commercial surfactant in non-polar solvents is investigated in Chapter 3. Anomalous solubility behaviour at low surfactant mole fractions is investigated and the underlying mechanisms are discussed. The importance of water to the aggregation behaviour of non-ionic surfactants is a recurring theme in the scientific literature. The interaction between a commercial non-ionic surfactant in non-polar solution and water is reported in Chapter 4. A mechanism is proposed to explain aggregation states which vary significantly with water content and its limitations are discussed.

Easily accessible oil reserves are currently decreasing, leading to an increase in more complex offshore deep-sea drilling programs, which require increasingly greater depths to be drilled. Such wells are commonly drilled using oil based muds, which leads to the production of drilled rock fragments, drill cuttings, which are contaminated with the base oil present in the mud. It is a legal requirement to reduce oil content to below 1 wt% in order to dispose of these drill cuttings in the North Sea and microwave processing is suggested as a feasible method of achieving the desired oil removal. However, there are currently gaps in our understanding of the mechanisms behind, and variables affecting, the microwave treatment of oil contaminated drill cuttings. The work described in this thesis seeks to address some of these gaps in knowledge. There were three main objectives for this thesis: (1) quantification, for the first time in the literature, of the main mechanisms driving oil and water removal during microwave processing of oil contaminated drill cuttings, (2) determination of key variables affecting performance during pilot scale continuous processing of oil contaminated drill cuttings and, for the first time, (3) treatment of drill cuttings with microwaves continuously at 896 MHz. Bench scale experiments carried out in a single mode applicator were used to quantify the mechanisms involved in oil and water removal from drill cuttings. It was found that both vaporisation and entrainment mechanisms play a role in oil and water removal. Vaporisation was the main mechanism of water and oil removal, and typically accounted for >80-90% of the water and oil removed. For oil removal, vaporisation of the oil phase accounted for 70-100% of the overall removal. The absolute amount of water entrained and vaporised was found to increase with increasing energy input and power density. However, as a percentage of the overall amount removed, entrainment was found to increase with increasing energy input. This was mainly due to higher heating rates at higher energy inputs, leading to pressurised, high velocity steam, which increased liquid carry-over (entrainment). Both the drill cuttings sample composition and applicator type were found to have an effect on the extent of entrainment/vaporisation. Samples consisting of a higher overall liquid content, tended to have a greater amount of surface liquid content. This led to a greater potential of carry over when steam generated internally left the sample. Increasing the power again led an increase in entrainment in this case. Different applicators were found to impact the electric field strength and power density within the water phase of the sample. Oil removal in multimode applicators progressed mainly through vaporisation (steam distillation) until the water content was sufficiently low to generate steam at a velocity high enough to entrain liquid droplets. When treatment was changed to single mode operation, entrainment occurred at an earlier stage, probably due to higher electric field strengths and power densities. It was also noted that the vaporisation mechanism of oil was more efficient at higher field strengths and powers, which could again be attributed to superheating and higher velocity steam, which enabled better mixing and heat transfer. Experiments were also run to determine the main variables affecting the performance of continuous processing of cuttings. Overall continuous processing showed a substantial improvement in the energy required, 150 kWh/t vs. >250 kWh/t, to reduce the oil content of a drill cuttings sample to 1 wt%. It was found that the initial water and oil content of the sample, as well as the sample particle size distribution, had the greatest effect on the efficiency of continuous processing. The effect of initial water and oil content on residual oil content was investigated methodically for the first time for continuous microwave processing of oil contaminated drill cuttings. An increase in initial oil content was found to have a significant impact on the energy input required to treat the sample to 1 wt% oil content. As the oil content increased, the energy input required increased exponentially, mainly as a result of the change in the physical structure of the sample. An increase in the water content led to an increase in energy input without any additional benefit to oil removal. However, as the water content was increased it was noticed that the theoretical energy input required to heat the entire sample approached the actual value measured for the energy input. This occurs as a result of the increasingly greater bulk dielectric properties of the sample as a result of higher levels of water content, which in turn leads to a higher efficiency in the conversion of microwave energy to heat in the sample. The effect of particle size on oil content distribution and removal was investigated. Oil content was found to be substantially higher in particles of size <1.0 mm, with removal also being significantly higher in this particle size range. However, as the majority of the samples tested, >80%, consisted of particles >1.0 mm, this improved removal is diluted by the performance of the coarser particles. The improved removal in finer particles is likely to be due to larger surface area, reduced path length within the particles and potentially higher electric field strength. Finally, samples processed continuously using a continuous microwave setup at 896 MHz showed improvements over both continuous microwave treatment at 2.45 GHz and bench scale setups. Increasing the f10wrate of the system at 896 MHz was also found to improve oil removal efficiency, which can be explained by the higher power requirements that would be required to maintain the energy inputs observed at the lower flowrate. Increasing the power leads to improved heating rates and thus increased removal rates through entrainment and vaporisation.