The underlying sustained demand for oil despite fluctuations in the oil price, and the requirement to replace dwindling reserves, both encourage oil companies to consider developing heavy oil reservoirs through implementation of EOR methods. Injection of air into the reservoir and initiation of a fire front causes the reservoir temperature to increase with a resulting decrease in the viscosity of the oil; this results in higher production rates and a better recovery factor. The main objective of this study is to investigate numerically the potential for applying the combustion process using a combination of real field data (from the Nimr field) and data from the literature, and to evaluate the overall process performance. This entails using a 2D cross-sectional model, which is constructed based on available field properties, to enable a detailed investigation of the fire front behaviour. The optimum operating conditions for the in-situ combustion process are determined by conducting a suite of sensitivity calculations. These sensitivity calculations are divided into two groupings, classified as well configurations and reservoir heterogeneities. Under both groupings, the modelling of the combustion process also considered the presence of the strong bottom water aquifer support. The results of this study suggest that the application of in-situ combustion in the heavy oil reservoir with strong bottom water aquifer is a technically viable proposition. The appropriate choice of well configurations is considered to be a vital component in the successful implementation of the combustion process, and leads to better process performance in terms of increasing the recovery factor. The presence of aquifer support should be regarded as a challenge to the initiation and sustaining of the fire front, and hence a carefully selected well placement plan (e.g. top-down) could make the difference between success and failure of the process. Depending on the well configurations selected, the impact of reservoir heterogeneities on the combustion process varied significantly. The combustion process recovery factor decreased as the fire front velocity changed, which is due to the large volume of coke been produced and deposited. This modelling study demonstrated the main approaches to optimise the combustion process performance, and while some data is field specific, the modelling results are generic.

Two phase flow of gas and condensate fluids in porous media is different from that of conventional Gas-Oil fluid systems. Such reservoirs are characterized by their complex phase and flow behaviors that significantly affect the well performance. The presence of retrograde fluid, when the pressure drops below dew point, and the dependency of the gas and condensate relative permeability (kr) on the velocity and interfacial tension (IFT) makes numerical modeling and performance prediction of gas condensate systems a real challenge, especially for complex well geometries such as hydraulically fractured wells (HFWs). The current research work is divided into three elements. The first one is devoted to study the flow behaviour around Single and Multi-layer hydraulically fractured wells (HFWs) in gas condensate reservoirs. Here, several in-house simulators have been developed for single-phase and two-phase gas condensate flow. The two phase in-house simulators correctly account for the phase change and the dependency of relative permeability to velocity and interfacial tension, due to inertia (reduction in kr as velocity increases) and coupling (improvement in kr as velocity increases and/or IFT decrease). The integrity of the in-house simulators have been verified by comparing some of their results with those obtained using the fine grid option of the ECLIPSE (E300) commercial reservoir simulator under the same prevailing flow conditions. Benefiting from, the 2 and 3-D in-house simulators a large data bank has been generated covering a wide range of variations of pertinent geometrical and flow parameters. Then, a new formula is proposed for estimation of an effective wellbore radius of an equivalent open-hole (EOH) radial 1-D system replicating flow around the 2 and 3-D HFW systems. The proposed formulation is general, in the sense that if the total gas fractional flow (GTR) is unity, then it correctly converts to that suitable for single phase gas system under Non-Darcy flow conditions and when Reynolds number is small to that under Darcy flow conditions. The second part of this thesis is devoted to study the optimization of hydraulic fracture geometry in gas condensate reservoirs. In this part of the study, a general optimum fracture design formulation is proposed based on the effective proppant number concept. In this new formula the maximum productivity index and optimum penetration ratio can be calculated for a certain proppant number, both accounted for the coupling and inertia effects. Here an effective proppant number formula is proposed (i.e. correcting the absolute proppant number for the effect of coupling and inertia). The proposed formula is general as it correctly converts to that suitable for single-phase Darcy and Non-Darcy flow. Furthermore, using the effective proppant number formula proposed here, the well-known Unified Fracture Design (UFD, Economides and Valko formula) has been modified to account for gas condensate flow conditions, i.e. coupling and inertia effects. The third part of this research work presents a thorough and extensive evaluation of the impact of the pertinent parameters on the clean-up efficiency process, which is often considered as one of the main reasons for the under-performance of hydraulic fracturing treatments, in gas reservoirs. In fact, most available clean up efficiency literature studies are concentrated on evaluating the impact of a single pertinent parameter at a time. That is, none of these studies have investigated the variation of all pertinent parameters simultaneously over a wide practical range of their variations, which may help in better understanding of the clean-up process and may provide practical guidelines to successful hydraulic fracturing jobs. Accordingly, this work embarked on a much more expanded study following statistical approaches. First, the key parameters which have significant impact on the gas production loss (GPL) are identified and then a 2-level full factorial statistical experimental design method has been used to sample a reasonably wide range of variation of pertinent parameters covering many practical cases for a total of 12 parameters. Since over 36,000 simulation runs were required, to cover the range of variation of all parameters, the simulation process has been simplified using a computer code, which was developed to automatically link different stages of these simulations. The analysis of the simulation runs using two response surface models (with and without interaction of parameters) demonstrates the relative importance of the pertinent parameters after different production time periods and provide a practical guidelines to a successful hydraulic fracturing job. In conclusion, this research cover the following main elements of HFW research, 1) – To propose simple numerical modelling methods for gas and gas condensate flow around single and multi-Layer HFWs, 2) – To propose a general Optimum Fracture Design method for gas and gas condensate reservoirs, which correctly account for the effects of coupling and inertia. 3) – To provide a thorough and extensive evaluation of the impact of pertinent parameters on clean-up efficiency of hydraulically fractured gas well.

No description available.

The microbial degradation of typical volatile petroleum hydrocarbons in an aerobic sandy soil was studied with and without the blending of 10 percent ethanol (E10) or 20 percent biodiesel (B20) in batch microcosms and minilysimeters. In the head-space of the mini-lysimeters all volatile compounds remained above the analytical detection limits over 92 days except toluene in the pure petroleum hydrocarbon mixture (PP) and ethanol in E10. The mass percentage of each petroleum hydrocarbon compound remaining at the end of the experiments was comparable for all fuel mixtures, except for m-xylene, which was significantly less reduced in E10 as compared to PP and B20. Total cell counts at the end of the experiments were highest for E10 and lowest for PP. DGGE analysis revealed a distinct microbial community structure for each fuel mixture. Batch studies confirmed these observations, in particular slower degradation of toluene in the presence of ethanol. Inorganic nutrient addition to the batch systems resulted in higher total cell counts, more rapid microbial degradation rates and more similar microbial community structures. Under aerobic conditions, competition for scare inorganic nutrients seems to be the most plausible reason for slower monoaromatic hydrocarbon biodegradation in the presence of more readily degradable biofuel.

As the world’s demand for crude oil increases and the amount of conventional reserves decline, the proportion of high acidity oils being produced is increasing, but this acidity can cause corrosion problems during production and refining. Total Acid Number (TAN) values are often used to predict whether a crude oil may cause corrosion problems and thus affect the value of the oil, although the relationship between TAN and the organic acid composition of oils is not fully understood. This thesis investigate the types of acidic compounds that contribute to acidity in crude oils and the geochemical factors that influence the compositions and concentrations of these compound classes in a suite of oils and bitumens from a variety of different locations, including the North Sea, Venezuela, Canada and California. This work in this thesis includes the development of a modified ASTM D664 titrimetric assay method for measuring acid numbers on small samples of heavy crude oil, core extracts and also isolated maltene and asphaltene fractions. The TAN values in the crude oils and their fractions analysed ranges from 0.04 to 21.24 (mg KOH/g). The results show that in general, the maltene fraction contributes most to the acidity in crude oils, however in some samples a large proportion of the oil TAN is contributed by the asphaltenes, even though they are quantitatively a small percentage of the oil. The geological reasons for the occurrence of oils with these highly acidic asphaltenes are not currently known. The analysis of isolated carboxylic acid fractions from ten oils of different origins, including those from different source depositional environments, levels of biodegradation and thermal maturity, using a gas chromatographic method, showed that the concentrations of total carboxylic acids corresponded well with TAN and biodegradation, indicating that these acidic compounds may be a major control on the acidity in crude oils and that the concentration of these were in turn controlled by the extent of biodegradation. ii Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) was used to characterise a set of North Sea crude oils with TAN values ranging from 0.11 to 7.58 (mg KOH/g oil). This showed that the O2 compound class (assumed to be mainly carboxylic acid “COOH” species) appeared as the dominant compound class under the analytical conditions used, with a strong correlation (r2 = 0.989) of the O2/N ratio with the TAN values of the oils, indicating that these compounds may control the TAN in these samples. This observation also applied to their maltene and asphaltene fractions. The dominant acid species in the high acidity North Sea oils, maltenes and asphaltenes were three and four ringed naphthenic acids. As the TAN of the oils increased, the double bond equivalent (DBE) distributions shifted to higher values indicating that their molecular structures became more highly aromatic. Fourier Transform Infrared (FTIR) spectroscopy potentially offers a much more rapid analysis of acids in oils compared to the ASTM D664 method. This study included the development of a rapid method for the determination of TAN by FTIR spectroscopy of conventional and heavy crude oils using single bounce attenuated total reflectance (ATR) and multi bounce horizontal HATR accessories. Using multivariate data analysis software, a multivariate model that correlates infrared spectra with the TAN value was developed using carbonyl (C=O) absorption bands ranging from 1770 to1650 cm-1. It was found that the correlation of FTIR measured TAN versus ASTM D664 measurements, obtained by multi bounce HATR (r2 = 0.943) were better than correlations produced by single bounce ATR (r2 = 0.812). Based on these findings, the measurement of oil acidity and TAN using FTIR is simpler and faster and also allows the analysis of small sample sizes and avoids other problematic issues such as the fouling of electrodes that can be experienced using the ASTM D664 standard method.

A short duration engine test has been developed with a view to assess the behaviour of lubricating oi1s under high crankcase temperature conditions met with in service. A comparison is made with the 100 hours American Lauson Engine test by using the standard American reference oil REO - 8 - 45 in the two test beds and run at identical crankcase temperatures. The test technique involves a constant observation of deterioration of the crankcase oil by acid values determined at intervals during a test, in addition to rating of piston and engine at the completion of such a test. With this test bed, the effectiveness of petroleum sulphonates having calcium, strontium, barium, zinc and aluminium as metal radical are studied at these high crankcase temperatures. Also the behaviour of the following inhibitors are observed. 1. Diphenyl Amine . 2. Tributyl Phosphite. 3. Organic Sulphur Phosphorus compound. 4. Organic Sulphur Phosphorus compound with zinc. The effect of viscosity characteristics of various base stocks on engine cleanliness, load carrying capacity and oil consumption rates are clearly brought out.

The combination of growing energy demands, the declining performance of conventional oil fields and attractive oil prices have renewed interest in both Heavy Oil resources (HO) and the methods of exploiting them. The vast volume of these resources notwithstanding, their low reservoir-scale mobility precludes exploitation using traditional primary and secondary recovery techniques, making enhanced oil recovery (EOR) methods (both thermal and non-thermal) natural candidates. However, the influence of several factors, technical and non-technical, require that rigorous studies inform the choice of EOR method(s). HO is a thick, viscous, tar-like crude oil that does not pump easily or flow well. This presents huge challenges when estimating reserves and extracting them from the reservoir, as does pipeline transportation to refineries. Increasingly, focus is moving towards those technologies that can most efficiently recover and process HO. The challenge here is finding the best way to produce, transport and process the oil. In this study, the focus is on how to identify the best way to recover the HO medium from an unconsolidated sand stone reservoir; to achieve this aim the Lower Fars formation in Kuwait is used as an exemplary case to test our screening methodology and to discover the best strategies. At present, Kuwait is pursuing a national objective to produce 4 million barrels per day (b/d) of oil by the year 2020. However, this target can only be achieved sustainably with HO development. Although there is evidence in the Kuwait Oil Company's (KOC) long-term plan that this is understood, there is not yet a clear-cut strategy for its realisation. Hence, the primary objective of this study is to establish possible development options for the medium heavy oil reservoirs. Other objectives include understanding the physics of selected thermal EOR processes in different medium heavy oil reservoirs and developing a robust screening tool for HO resources. Numerical modelling studies will be used to achieve these objectives. Given the huge number of EOR methods and their various combinations, it is not pragmatic to conduct detailed studies on each method for potential application to the reservoir. To accelerate decision-making, using experiences taken from field performances elsewhere, a relatively simple screening procedure has been developed and implemented. Using this tool, less favourable options have been eliminated, retaining only the 'best' options for further evaluation; these are unheated-water flooding, hot water flooding, Steam flooding (SF) and cyclic steam stimulation (CSS). For the preliminary numerical simulations, a homogenous, three-phase and multi-component numerical model was constructed using the known (average) geological, petrophysical and fluid properties of the Northern sector of the Ratqa field. Information from analogue fields and correlations was also used to complete the data. The reservoir was considered homogeneous in the first part of the study, allowing for the separation of process effects from reservoir geology. The second part of this study presents the results of the sensitivity study on a small scale model, extracted from a large field scale sector model of 0.9 Million cells. Several simulation runs were conducted to investigate the effects of petrophysical properties and operating variables on the performance of unheated-water flood, hot water flood, steam flood processes, and CSS. The simulation results show that any positive impacts from thermal injection on oil production are not instantaneous - they only become noticeable after an appreciable number of pore volumes have been injected. This finding is attributed to the time lag required to heat up the reservoir to a temperature that gives reasonable reduction of oil viscosity, creating a more favourable mobility ratio. In addition to giving a higher ultimate recovery rate, the preliminary results also indicate that high-temperature operation accelerates performance. From an economic viewpoint, production acceleration would improve overall project economics by mitigating the negative impact of discounting on the revenue stream. Another important finding from the simulation study is that while hot water flood is characterised by a stable displacement of oil by water, unstable fronts are evident in the cold-water process, resulting in a significant quantity of by-passed oil. When conducting the study it was also imperative to conduct a detailed economic analysis to assess the economic feasibility of each recovery process/case. To achieve this, a preliminary matrix of the main factors was integrated into the developed economic model. The input for project performance specified cumulative oil recovery (income) versus cumulative energy injected into the reservoir in terms of heated fluids (cost). Continuing the work to investigate the best development options for a major unconsolidated, shallow HO reservoir a comparative study and a sensitivity analysis of various operational conditions and reservoir parameters were conducted in order to: (1) find the best conditions to achieve a high RF, and (2) to understand the effect of reservoir heterogeneity on the reservoir's performance. The operational parameters investigated are injected fluid type, injection swapping time and the perforation location. The reservoir parameters examined are oil viscosity, initial water saturation, porosity and permeability. In addition to studying these reservoir parameters, oil price sensitivity was investigated to evaluate the financial feasibility of the selected recovery methods within both the historical and forecasted oil price range. The preliminary results show that the recovery factor (RF) is very sensitive to the oil viscosity value and the relationship between them is nonlinear. The simulation results also indicate that an increase in the porosity and permeability accelerates performance; however, the opposite is not true of the initial water saturation value. From an economic perspective, production acceleration would improve overall project economics by mitigating the negative impacts of discounting on the revenue stream due to the low oil price. Economically, successive (combination of injected fluids) cases support successful investment at the lowest (expected) oil price; in contrast, the continuous steam and hot water flooding development options show a higher economic risk after the second year. This work contributes significantly towards our understanding of the performance of different development options in high permeability HO reservoirs. This is critical for the decision making process when determining the applicability of EOR recovery methods and their successful application in the field.

No description available.

Over the years, several attempts have been made by various research institutions and petroleum companies to develop models for the prediction of CO2 corrosion in pipelines, in order to better capture the underlying principles that cause it. Modelling CO2 corrosion is important to the oil and gas and carbon capture and storage (CCS) industries, as it provides the means by which the prevention of the financial costs from lost production, the preservation of the environment as well as the health and safety of human lives can be achieved. In this thesis, existing models have been investigated and compared against newly derived models in terms of their accuracy of prediction, by using an identical test dataset. A neural network (NN) model was developed, in which a detailed sensitivity analysis was carried out on Matlab training functions to determine their degree of suitability in CO2 corrosion prediction. Results showed that the tansig transfer function was the most suitable and that a 2-layer network was sufficient to obtain desirable R2-values of ~0.9 for both low and high pressure CO2 corrosion data. Also, a linear regression model was developed based on predictor variables: temperature (T), CO2 partial pressure (PCO2), fluid velocity (U) and pH, for both low and high pressure CO2 data. The respective R2-values obtained are 0.65 and 0.7. An R2-value of 0.8 can be achieved for the low pressure CO2 data; however the derived regression equation is inelegant and contains a combination of a large number of predictor terms. From Monte Carlo analyses, the exponential and normal distributions were discovered to be the best fits for the low and high pressure CO2 corrosion rate data, respectively. Further, parametric sensitivity analyses revealed the pH and fluid velocity to be the least and most significant variables for low pressure CO2, respectively, while the velocity and temperature were the least and most significant variables for high pressure CO2 corrosion, respectively.

No description available.