Search

The development of shale gas resources is subject to technical challenges and markedly affected by volatile markets that can undermine the development of new projects. Consequently, stakeholders can greatly benefit from decision‐making support tools that integrate the complexity of the system along with the uncertainties inherent to the problem. Accordingly, a general methodology is proposed in this work for the evaluation of integrated shale gas and water supply chains under uncertainty. First, key parametric uncertainties are identified from a candidate pool via a global sensitivity analysis based on a deterministic optimization model. Then, a two‐stage stochastic model is developed considering only the key uncertain parameters in the problem. Moreover, the merits of modeling uncertainty and implementing the stochastic solution approach are evaluated using the expected value of perfect information and the value of the stochastic solution metrics. Furthermore, the conditional value‐at‐risk approach was implemented to evaluate different risk‐aversion levels and the corresponding impacts on the shale gas development plan. The proposed methodology is illustrated through two real‐world case studies involving six and eight potential well‐pad locations and two options of well‐pad layouts.

Shale gas has gained importance in the energy landscape in recent decades. However, its development has raised environmental concerns, especially, those associated with water management. Thus, the assessment of water management aspects, which inevitably impact the economic aspects, is crucial in evaluating the merits of any project exploiting this energy source. This paper provides a review of the economic and environmental implications of shale gas development around the world. Furthermore, to demonstrate the interplay between the various technical, environmental and economic factors in concrete terms, we report on a specific set of case studies conducted using an integrated decision-support tool that has been implemented to model and optimize shale gas development projects. The case study results confirm that the gas breakeven price decreases with expansion in scale of the shale gas development, i.e. increasing the number of well-pads in the system. However, scale also increases the options for water re-use and recycle in drilling and fracturing operations, which can result in lower freshwater withdrawal intensity. Moreover, under water scarcity scenarios, the choice of well-pad designs that are inherently less water intensive was found to be more cost-effective than water re-use or/and recycle strategies at reducing net freshwater demand. Similar trends were observed when the impact of wastewater quality, i.e. total dissolved solids concentration, on the optimal development strategy of shale gas plays was investigated. The results of these case studies reveal that greater efforts are needed at characterizing freshwater availability and wastewater quality for the evaluation of both the economic and environmental aspects of shale gas development.

This work investigates the impact of pretreatment technologies in the design of BioSNG supply chains at a regional and national scale. For this purpose, an optimisation-based framework is proposed to account for two possible routes for BioSNG production. The first route considers processing of raw biomass and production of BioSNG in integrated facilities. The second route consists of pretreatment technologies, transportation of intermediate products, and upgrading facilities. The main objective is to investigate the trade-off between capital investment and reduction of transportation costs, and their impact on the economic performance of a BioSNG supply chain. Moreover, the impact of government subsidisation is further investigated through a parametric analysis in which the tariff is varied from £0/MWh up to £100/MWh. Finally, the major contributing factors in the design of BioSNG supply chains are identified through the implementation of a rigorous global sensitivity analysis (GSA). The results suggest that inclusion of pretreatment technologies improve considerably the economic performance, however, their impact is not enough to detach the development from government subsidisation which influences tremendously the possibility of a large-scale deployment.

A general optimisation framework based on a spatially-explicit multiperiod mixed integer linear programming (MILP) model is proposed to address the strategic design of BioSNG supply chains. The framework considers procurement of feedstocks, plantation of energy crops, and different modes for transportation of feedstocks and final products. The mathematical framework allows researches and policy makers to investigate scenarios that promote the development of BioSNG supply chains in a regional and/or national context. The capabilities of the proposed model are illustrated through the implementation of a set of case studies based on the UK. The results revealed that domestic resources in the UK can supply up to 21.4% of the total gas demand projected by the UK National Grid in the scenario “Slow progression” for a planning horizon of 20 years. However, despite the considerable potential for production of BioSNG, the role of the government through subsidisation schemes such as feed-in tariff and Renewable Obligation Certificates (ROCs) is crucial in order to make the development of these resources economically attractive for private sectors.

The use of agricultural residues for bioethanol production greatly depends on availability of raw materials and the proper design of a flexible multi-feedstock facility. Therefore, this article assesses the economic, environmental, and social feasibility of a bioethanol production plant, using multiple coffee crops residues (stems, pulp, and mucilage). A case study was designed for the Colombian context, considering three scenarios for different capacity plant. Results suggest that the production costs of 0.504, 0.508, and 0.515 $USD/l for large, medium and small capacity, respectively, are comparable to the bioethanol market price and are similar to other studies reported in the literature. The CO2 emissions obtained were 1.296 Kg CO2/l, 1.297 Kg CO2/l and 1.3 Kg CO2/l for the large, medium, and small plants respectively. The large plant requires 1,170 million tons per year of fresh water, and generates a gray water footprint of 119 thousand tons per year. However, without recirculation, 2.87 times more water is required. Favorable results were identified in terms of reduction of collateral environmental effects, as well as positive impacts on social aspects. Finally, a sensitivity analysis shows the impacts of key parameters on economic, social, and environmental merits of producing bioethanol from coffee residues.

This study presents the mathematical formulation and implementation of a comprehensive optimization framework for the assessment of shale gas resources. The framework simultaneously integrates water management and the design and planning of the shale gas supply chain, from the shale formation to final product demand centers and from fresh water supply for hydraulic fracturing to water injection and/or disposal. The framework also addresses some issues regarding wastewater quality, i.e., total dissolved solids (TDS) concentration, as well as spatial and temporal variations in gas composition, features that typically arise in exploiting shale formations. In addition, the proposed framework also considers the integration of different modeling, simulation and optimization tools that are commonly used in the energy sector to evaluate the technical and economic viability of new energy sources. Finally, the capabilities of the proposed framework are illustrated through two case studies (A and B) involving 5 well-pads operating with constant and variable gas composition, respectively. The effects of the modeling of variable TDS concentration in the produced wastewater is also addressed in case study B.

The U.S. Department of Energy is promoting the development of technologies that tackle gas flaring activity in oil production. Among these technologies, injection of flare gas into the reservoir to stimulate production of oil and capture the injected gas has received attention. Accordingly, this study contributes to understanding the economic and environmental implications of implementing enhanced oil recovery (EOR) in shale oil development to reduce gas flaring. A systematic optimization-based methodology is proposed to fully integrate the development of a shale oil field along with EOR projects. The framework optimizes decisions such as drilling schemes, workover of depleted production wells, pipeline and processing infrastructure, location of injection sites, injection rates, and duration of EOR operations. The pertinence of implementing EOR in the Bakken area is addressed through a typical production unit with 18 wellpads, which is further extended to 4 production units (72 wellpads). Results reveal consistent values across different development scales for operational variables such as percentage of wellpads undergoing EOR, incremental produced oil, percentage of total gas production used for injection, and average gas flaring. Conversion of depleted wellpads is preferred over installation of new injection wells. A global sensitivity analysis revealed the dominant role of EOR efficiency over Capex, Opex, and gas-oil ratio. EOR greatly favors the economics and the reduction of gas flaring but it is insufficient to comply with local flaring targets. Nonetheless, the implementation of EOR in combination with taxation tariffs is an adequate mechanism to reduce gas flaring and comply with regulatory targets.

Climate change becomes increasingly more relevant in the context of water systems planning. Tools are necessary to provide the most economic investment option considering the reliability of the infrastructure from technical and environmental perspectives. Accordingly, in this work, an optimisation approach, formulated as a spatially-explicit multi-period Mixed Integer Linear Programming (MILP) model, is proposed for the design of water supply chains at regional and national scales. The optimisation framework encompasses decisions such as installation of new purification plants, capacity expansion, and raw water trading schemes. The objective is to minimise the total cost incurring from capital and operating expenditures. Assessment of available resources for withdrawal is performed based on hydrological balances, governmental rules and sustainable limits. In the light of the increasing importance of reliability of water supply, a second objective, seeking to maximise the reliability of the supply chains, is introduced. The epsilon-constraint method is used as a solution procedure for the multi-objective formulation. Nash bargaining approach is applied to investigate the fair trade-offs between the two objectives and find the Pareto optimality. The models' capability is addressed through a case study based on Australia. The impact of variability in key input parameters is tackled through the implementation of a rigorous global sensitivity analysis (GSA). The findings suggest that variations in water demand can be more disruptive for the water supply chain than scenarios in which rainfalls are reduced. The frameworks can facilitate governmental multi-aspect decision making processes for the adequate and strategic investments of regional water supply infrastructure. Refereed/Peer-reviewed

Shale gas production has been the focus of intense debate in recent years. Shale gas supporters claim that it could be the way to transition between fossil fuels and renewable energy sources. For instance, in the United States, power generation from coal is being replaced by power generation from natural gas, which is a cleaner fuel when compared to coal. However, shale gas critics claim that the environmental cost associated with shale gas production is high enough to negate the benefits to society. For example, high water usage as well as the potential for contamination of underground and surface water sources constitute important environmental challenges for the development of shale gas resources. This study presents a methodology for the preliminary assessment of the development of shale gas resources taking into account well-pad design as one of the most important decision variables. To perform the assessment, different performance metrics are proposed to evaluate not only the economics of developing...

This chapter is intended to discuss the application of mathematical programing methodologies to assist in the design and planning of energy supply chains. Accordingly, a comprehensive literature review of various different energy systems models as well as optimization approaches which have been developed to support capacity planning and investment decisions is presented. Two mathematical programming-based frameworks, one for shale gas supply chains and another for interconnected power systems are briefly described and employed for relevant case studies. These case studies are used not only to illustrate the methodology but more importantly to draw some insights that are relevant to policy development.

This study addresses the quantification of the impact of wastewater quality, i.e. Total Dissolved Solids (TDS) concentration, on both the economics and the water management strategy associated with the development of shale gas resources. The impact of TDS concentration in wastewater on the water management strategy is quantified in term of the variation of water demand and the share of fresh water in the optimal water supply mix. Similarly, the net present value (NPV) and breakeven cost are used in order to measure the impact of the TDS concentration on shale play economics.

In this work, an optimization framework to support the planning of the development of shale gas resources is proposed. Financial aspects are taken into account through the integration of financing options, such as own capital, and external sources, short and long term bank credit lines. The model also includes the design of well-pads in terms of total number of wells, and length and number of hydraulic fractures completed at each well. In addition, different capacities and locations are considered for compressor stations, gas separation plants, and water treatment plants. A case study involving two alternative financing strategies was conducted to demonstrate the capabilities of the model. It is found that external financing can play an important role in the development of a shale gas field, achieving an increase in net profit of almost 65 % when compared to a scenario where only own capital is considered.

The transport of long gas bubbles, suspended in liquid, through symmetric bifurcations, is investigated experimentally and theoretically as a model of cardiovascular gas bubble transport in air embolism and gas embolotherapy. The relevant dimensionless parameters in the models match the corresponding values for arteries and arterioles. The effects of roll angle (the angle the plane of the bifurcation makes with the horizontal), capillary number (a dimensionless indicator of flow), and bubble volume (or length) on the splitting of bubbles as they pass through the bifurcation are examined. Splitting is observed to be more homogenous at higher capillary numbers and lower roll angles. It is shown that, at nonzero roll angles, there is a critical value of the capillary number below which the bubbles do not split and are transported entirely into the upper branch. The value of the critical capillary number increases with roll angle and parent tube diameter. A unique bubble motion is observed at the critical capillary number and for slightly slower flows: the bubble begins to split, the meniscus in the lower branch then moves backward, and finally the entire bubble enters the upper branch. These findings suggest that, in large vessels, emboli tend to be transported upward unless flow is unusually strong but that a more homogeneous distribution of emboli occurs in smaller vessels. This corresponds to previous observations that air emboli tend to lodge in the upper regions of the lungs and suggests that relatively uniform infarction of tumors by gas embolotherapy may be possible.

Embolotherapy involves the occlusion of blood flow to tumors to treat a variety of cancers, including renal carcinoma and hepatocellular carcinoma. The accompanying liver cirrhosis makes the treatment of hepatocellular carcinoma by traditional methods difficult. Previous attempts at embolotherapy have used solid emboli. A major difficulty in embolotherapy is restricting delivery of the emboli to the tumor. We are developing a novel minimally invasive gas embolotherapy technique that uses gas bubbles rather than solid emboli. The bubbles originate as encapsulated liquid droplets that are small enough to pass through capillaries. The droplets can be selectively vaporized in vivo by focused high intensity ultrasound to form gas bubbles which are then sufficiently large to lodge in the tumor vasculature. We investigated the dynamics of bubble lodging in microfluidic model bifurcations made of poly(dimethylsiloxane) and in theoretical analyses. The results show that the critical driving pressure below which a bubble will lodge in a bifurcation is significantly less than the driving pressure required to dislodge it. Based these results, we estimate that gas bubbles from embolotherapy can lodge in vessels 20 μm or smaller in diameter, and conclude that bubbles may potentially be used to reduce blood flow to tumor microcirculation.Copyright © 2007 by ASME

Lodging of cardiovascular gas bubbles is investigated in a microfluidic model of small arteriole bifurcations. These experiments address the dynamics of the lodging mechanism of gas bubbles in bifurcations. This work is motivated by a novel gas embolotherapy technique for the potential treatment of cancer by tumor infarction. The experimental model arteriole bifurcations were constructed from a transparent elastomer (polydimethylsiloxane). A single air bubble was suspended in water within the parent tube of the bifurcation and a specified driving pressure was imposed via constant elevation reservoirs that were open to atmospheric pressure. The driving pressure and bubble size were varied, and their effects on the bubble lodging were assessed. The results show that the pressure to lodge a bubble in a bifurcation is less than to dislodge it. It was also possible to occlude an entire bifurcation and multiple bifurcation devices with bubbles. Splitting ratios were assessed in the range of lodging to dislodging pressure where we observed an instability in bubble splitting. From the results we estimate that gas bubbles from embolotherapy can lodge in vessels 21 mum or smaller in diameter. These findings may be useful in developing strategies for microbubble delivery in gas embolotherapy

Lodging of cardiovascular gas bubbles is investigated in a microfluidic model of small arteriole bifurcations. This work is motivated by a novel gas embolotherapy technique for the potential treatment of cancer by tumor infarction and by air embolism. The experimental model arteriole bifurcations were constructed from a transparent elastomer, poly(dimethylsiloxane), using soft lithography. A single air bubble was suspended in water within the parent tube of the bifurcation and a specified driving pressure was imposed via constant elevation reservoirs that were open to atmospheric pressure. The driving pressure and bubble size were varied, and their effects on the bubble lodging were assessed. These findings may be useful in developing strategies for microbubble delivery in gas embolotherapy.

Motivated by a developmental gas embolotherapy technique for selective occlusion of blood flow to tumors, we examined the transport of a pressure-driven semi-infinite bubble through a liquid-filled bifurcating channel. Homogeneity of bubble splitting as the bubble passes through a vessel bifurcation affects the degree to which the vascular network near the tumor can be uniformly occluded. The homogeneity of bubble splitting was found to increase with bubble driving pressure and to decrease with increased bifurcation angle. Viscous losses at the bifurcation were observed to affect the bubble speed significantly. The potential for oscillating bubble interfaces to induce flow recirculation and impart high stresses on the vessel endothelium was also observed.

The lodging mechanisms and dynamics of cardiovascular gas bubbles are investigated in microfluidic model bifurcations made of poly(dimethylsiloxane). This work is motivated by gas embolotherapy for the potential treatment of cancer by tumor infarction. The results show that the critical driving pressure below which a bubble will lodge in a bifurcation is significantly less than the driving pressure required to dislodge it. From the results the authors estimate that gas bubbles from embolotherapy can lodge in vessels 20μm or smaller in diameter, and conclude that bubbles may potentially be used to reduce blood flow to tumor microcirculation.