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This contributed volume presents a multi-perspective collection of the latest research findings on oil and gas exploration and imparts insight that can greatly assist in understanding field behavior, design of test programs, and design of field operations. With this book, engineers also gain a powerful guide to the most commonly used numerical simulation methods that aid in reservoir modelling. In addition, the contributors explore development of technologies that allow for cost effective oil and gas exploration while minimizing the impact on our water resources, surface and groundwater aquifers, geological stability of impacted areas, air quality, and infrastructure assets such as roads, pipelines, water, and wastewater networks. Easy to understand, the book identifies equipment and procedural problems inherent to oil and gas operations and provides systematic approaches for solving them.



Chapter 1. Understanding Asphaltene Aggregation and Precipitation Through Theoretical and Computational Studies

Asphaltenes are known to cause serious problems during the processing of petroleum compounds due to their aggregation and precipitation behaviors. Despite the significant amount of experimental works that have been performed, large debates still exist in literature. Parallel with experimental work, great efforts have been spent from theoretical and computational perspectives to predict asphaltene behaviors under given conditions, to provide atomic/molecular information on their aggregation as well as precipitation, and to further shed lights on existing debates. This chapter presents a detailed review of previous theoretical and computational works on asphaltene aggregation and precipitation. Theoretical models developed, systems simulated, and the key findings are summarized; and discrepancies among those works are highlighted.
Cuiying Jian, Tian Tang

Chapter 2. Advancement in Numerical Simulations of Gas Hydrate Dissociation in Porous Media

The amount of research on gas hydrates has been rising dramatically due to the significant role gas hydrates play as a persistent trouble for gas industry, a promising energy source, and a potential threat to environment. In the energy exploration perspective, numerical simulations play a major role in improving our understanding of the fundamentals gas hydrate dissociation as well as hydrate reservoir behaviors. This chapter presents an integrative review on the computer simulation models of gas hydrate dissociation, which have boomed since their first appearance in 1980s. Necessary background knowledge for gas hydrates and the existing investigations on this topic are firstly summarized. A unified framework is then developed for the purpose of integrating and classifying the existing models. The major mechanisms involved in the phase change process are illustrated and explained on the level of governing equations. The similarities and discrepancies among the models are demonstrated and discussed using this framework. Discussions continue on the auxiliary relationships for describing the material properties based on their categories. The various auxiliary relationships employed in the existing computational models are summarized and compared. Finally, the results obtained by previous simulations as well as other laboratory or field data are discussed. Noteworthy trends in the numerical simulations of gas hydrates behaviors are also unveiled. Recommendations are provided for future research. By providing an overview of the topic area, this chapter intends to provide scientific basis to understand the existing gas hydrate simulation models as well as serve as a guide for future research on advanced gas hydrate simulations.
Zhen Liu, Xiong Yu

Chapter 3. Discrete Element Modeling of the Role of In Situ Stress on the Interactions Between Hydraulic and Natural Fractures

The interaction between HF (hydrofractures) and NF (natural fractures) is a complex-coupled process which involves several physical parameters. Despite numerous previous works, the respective role of in situ stress, natural fracture properties, and orientations is still difficult to assess. In this chapter, a fully hydromechanical coupled numerical model has been used to simulate different three-dimensional configurations. These configurations provide insight into how a natural fracture is mechanically or hydraulically activated depending on well-defined parameters. It has been shown that the natural fracture can be either activated hydraulically without any shear displacement or mechanically activated while not loaded hydraulically. These configurations are controlled at a first-order level by the combination of the in situ differential stress state and the natural fracture orientation.
Riccardo Rorato, Frédéric-Victor Donzé, Alexandra Tsopela, Hamid Pourpak, Atef Onaisi

Chapter 4. Rock Physics Modeling in Conventional Reservoirs

Seismic reservoir characterization focuses on the interpretation of elastic attributes, such as seismic velocities and impedances, estimated from geophysical data such as surface seismic, crosswell seismic, and well log data. Elastic attributes depend on rock and fluid properties. The discipline of rock physics investigates the physical relations between petrophysical properties of porous rocks and their elastic response. In this chapter, we review the most common rock physics models for conventional hydrocarbon reservoirs. Rock physics models are commonly used to study the effect of variations in porosity, lithology, fluid saturation, and other petrophysical properties in reservoir rocks and the changes in the corresponding elastic and seismic response. These models can then be used to quantitatively interpret geophysical data and build reservoir models conditioned by well log and seismic data.
Dario Grana

Chapter 5. Geomechanics and Elastic Anisotropy of Shale Formations

Deep shales are the most abundant yet least characterized sedimentary rocks in petroleum industry while they have become significant sources of hydrocarbon unconventional resources. This chapter aims to fulfill an investigation of anisotropy in this rock type in several different facets through integration of field and lab data. I seek to generate key information to better understand elastic anisotropy as well as in situ stresses to better perform drilling, well completion, perforating, and hydraulic fracturing for the purpose of geomechanical modeling.
The first step was to study the anisotropic behavior of shale formations. For such a purpose three necessary independent shear moduli, elastic stiffness coefficients, and principal stresses are calculated and measured. The parameters then are used to generate shear radial profiles and slowness-frequency plots to analyze formation anisotropy, type, and origin.
The next step was to evaluate direction and magnitude of the minimum and maximum anisotropic principal horizontal stresses as the governing element in geomechanical modeling. I also analyzed wellbore behavior and predicted wellbore failure under stress alteration caused by drilling. Elastic anisotropy of the formation is considered in 3D numerical models and calculations, which has improved the results considerably.
Mehdi Ostadhassan

Chapter 6. Nano-Scale Characterization of Organic-Rich Shale via Indentation Methods

Gas shale or organic-rich shale is a porous multi-scale material that consists essentially of clay, silt inclusions, air voids, and kerogen, which is gaseous organic matter. Assessing the mechanical behavior of gas shale across several length scales is a challenging task due to the complex nature of the material. Therefore, the aim of this investigation is to introduce a novel framework based on nano-mechanics to characterize the elastic and plastic properties of gas shale using advanced techniques such as scanning electron microscopy (SEM), statistical nano-indentation, and micromechanical modeling. An indentation consists in pressing a diamond stylus against a soft material and measuring both the Young’s modulus and hardness from the force and penetration depth measurements. Meanwhile, the grid indentation technique consists in carrying out a large array of indentation tests and applying statistical analysis so as to represent the overall behavior as the convolute response of several individual mechanical phases. The specimens analyzed in this study were extracted from major gas shale plays in the USA—Antrim shale from the Michigan Basin in Michigan State and Barnett shale from the Bend Arch-Fort Worth Basin in Texas—and in France—Toarcian shale from the Paris Basin. SEM reveals a heterogeneous granular microstructure with the grain size ranging from 30 to 100 μm; meanwhile, statistical indentation enables to identify the basic micro-constituents. Finally, micromechanics theory makes it possible to bridge the nanometer and macroscopic length scales. The field of applications is vast including major energy-related schemes such as hydrocarbon recovery for oil and gas wells, carbon dioxide geological sequestration, or nuclear waste store in depleted wells.
Ange-Therese Akono, Pooyan Kabir

Chapter 7. On the Production Analysis of a Multi-Fractured Horizontal Well

This paper investigates the post fracture transient analysis of multi-fractured horizontal wells under the assumption of infinitely large fracture conductivity. Most of the existing studies of multi-fractured wells have considered finite fracture conductivity, when the dynamic fluid pressure drop in the flow within fractures is a part of the solution. This led to computationally intensive solution methods, particularly when a reasonably large number of fractures representative of current field applications is considered. In this work, we limit our consideration to low-permeability, tight (e.g., shale) reservoirs, when pressure losses in propped fractures can be neglected. This assumption allows to develop a rigorous, accurate, and computationally efficient solution method based on the fundamental problem of a unit step pressure decline in an array of identically sized and equally spaced fractures. The study of this fundamental problem is analogous to the well testing analysis of a fractured well produced at constant bottom-hole pressure conditions. The solution for a unit step pressure decline is used within the Green’s function framework to formulate and solve for the transient pressure response of a multi-fracture array produced at a constant volumetric flow rate. We also explore two simplified approaches to the production analysis of multi-fractured wells based on (1) the infinite fracture array approximation for finite arrays, and (2) an extension of the ad hoc method of Gringarten et al. (Soc Pet En J 14(04):347–360), respectively. We show that both methods lead to very good approximations of the rigorous solution for a finite fracture array problem, thus allowing to further simplify the transient analysis of multi-fracture wells.
Erfan Sarvaramini, Dmitry I. Garagash

Chapter 8. Interfacial Engineering for Oil and Gas Applications: Role of Modeling and Simulation

Interfaces control the functional performance of advanced materials used in the oil and natural gas industry for applications ranging from oil recovery, and flow assurance to gas separation, and carbon capture and utilization. The interactions that govern such functional performance are extremely challenging to obtain empirically. This is partly because of the instability at fluid interfaces, but also due to the intrinsic complexity in quantification of the behavior of a large number of components and interactions. Molecular modeling offers a pathway to examine confined wettability, specific adsorption, and cooperative network formation with changes in chemical structure that act as a design platform for custom functional performance. This is especially important in oil and natural gas processing because of the large number of variations introduced through changes in environment from one location to another. This chapter highlights the iterative design of injection fluids, kinetic inhibitors, separation membranes, and conversion technologies through mechanistic insight gained from simulations primarily based on molecular dynamics and density functional theory approaches.
Kshitij C. Jha, Vikram Singh, Mesfin Tsige

Chapter 9. Petroleum Geomechanics: A Computational Perspective

Petroleum geomechanics is concerned with rock and fracture behavior in reservoir, drilling, completion, and production engineering. Typical problems in petroleum geomechanics include subsidence, borehole stability, and hydraulic fracturing. All are coupled problems that involve heat transfer, fluid flow, rock/fracture deformation, and/or solute transport. Numerical solutions through modeling are desired for such complicated systems. In this chapter, we present the mathematical descriptions of these typical problems in petroleum geomechanics, point out the challenges in solving these problems, and address those challenges by a variety of classical and emerging numerical techniques.
Maurice B. Dusseault, Robert Gracie, Dipanjan Basu, Leo Rothenburg, Shunde Yin

Chapter 10. Insights on the REV of Source Shale from Nano- and Micromechanics

Nano. In the past decade, chemical, physical, and mechanical characterization of source rock reservoirs has moved towards micro- and nano-scale analyses. This is primarily driven by the fact that the representative elementary volume (REV) for characterizing shales is at the nanometer scale. Nanoindentation is now used in many industrial and university laboratories to measure both stiffness and strength and other mechanical properties of materials, such as anisotropic Young’s moduli and plastic yielding parameters. However, standardized methods of testing and analysis are yet to be developed.
Micro. The shale matrix, composed of nano-granular clay and microscale non-clay minerals, also includes the hydrocarbon source material kerogen. This biopolymer is interbedded and intertwined with the clay and non-clay minerals at almost all scales. Kerogen not only has a Young’s modulus in compression but also has a substantial Young’s modulus value in tension and much higher tensile strength than rocks in general. This fact has now been observed at the micro- and nanoscale during nanoindentation while monitoring in situ via scanning electron microscopy (SEM). Load and unload experiments with micro-Newton forces (μN) and nanometer (nm) displacements have clearly shown the elastic nature of kerogen in the shale gas matrix.
Macro. Given that the organic matter has an elastic Young’s moduli in tension, and viscoelastic characteristics, it is therefore capable of re-healing the hydraulic fracture. This is a major reason for our more or less unsuccessful gas shale stimulations. Keeping the fracture open even after proppant placement has proven to not be enough for gas and oil shale optimal well productivity. New macro-scale testing techniques are needed to evaluate the mechanical properties of shales that have not been possible to imagine outside of recent advances in nano- and micro-scale analyses.
Katherine L. Hull, Younane N. Abousleiman

Chapter 11. Experimental and Numerical Investigation of Mechanical Interactions of Proppant and Hydraulic Fractures

Hydraulic fracturing has recently received a great amount of attention not only for its economic importance but also for its potential environmental impact. The basic intention of the hydraulic fracturing process is to increase the productivity of the stimulated well by maximizing the reservoir’s permeability, but the permeability of the fractured reservoir is strongly affected by the apertures of the fractures. Proppants are often utilized during hydraulic fracturing to aid the retention of the fracture aperture, and laboratory experiments and field observations have shown a strong correlation between the volume of proppant deployed in hydraulic fracturing operations and reservoir productivity. However, the factors controlling proppant performance in real rock fractures are still poorly understood. Considering the high cost of a hydraulic fracturing treatment, a more informed selection of design parameters, such as proppant size, shape, concentration and properties, fracture fluid viscosity, and pumping schedule is needed. A better understanding of the behavior of fluid and proppant within a fracture and their relationship to fracture conductivity is of great practical interest. The goal of this chapter is to provide a summary of recent experimental and numerical investigations on the interactions of proppant and hydraulic fractures.
Congrui Jin

Chapter 12. Integrated Experimental and Computational Characterization of Shale at Multiple Length Scales

Shale is known as a hydrocarbon source rock and is emerging as a potentially key component of the worldwide energy landscape via the recent development of hydraulic fracturing technique. A fundamental understanding of the fracturing behaviors of intact shale is the basis of any technological innovation aiming at increasing extraction efficiency. Considering the highly heterogeneous and fine-grained nature of shale, investigation and characterization should be conducted at multiple length scales. Through a brief overview of the experimental and computational studies for mechanical characterization of shale at different scales, this study investigates the possibility of integrating experimental and computational characterization research into a unified multiscale framework. Such multiscale framework is needed to predict macroscale shale fracturing behavior from the microscopic events. As preliminary results, an experimental characterization campaign of Marcellus shale at the macroscopic level and a micromechanical discrete model for predicting the mechanical behaviors of anisotropic shale are also presented.
Weixin Li, Congrui Jin, Gianluca Cusatis

Chapter 13. Recent Advances in Global Fracture Mechanics of Growth of Large Hydraulic Crack Systems in Gas or Oil Shale: A Review

This chapter reviews the recent progress toward computer simulation of the growth of vast systems of branched hydraulic cracks needed for the efficient extraction of gas or oil from shale strata. It is emphasized that, to achieve significant gas extraction, the spacing of parallel hydraulic cracks must be on the order of 0.1 m, which means that the fracturing of the entire fracking stage would require creating about a million vertical cracks. Another emphasized feature is that the viscous flow of fracking water along the hydraulic cracks must be combined with Darcy diffusion of a large amount of water into the pores and flaws in shale. The fracture mechanics on the global scale is handled by the crack band model with gradual postpeak softening and a localization limiter in the form of a material characteristic length. Small scale computer simulations demonstrate that the computational approach produces realistically looking results.
Zdeněk P. Bažant, Viet T. Chau

Chapter 14. Fundamentals of the Hydromechanical Behavior of Multiphase Granular Materials

The principal aim of this chapter is to describe the hydromechanical behavior of unsaturated soils based on experimental evidence. The unsaturated soils are media in which the pore space is occupied by more than a fluid, typically liquid and gas. They give rise to very characteristic types of geotechnical problem such as: the loss of strength associated with the increase in water content or degree of saturation and the damage to structure caused by the collapse for saturation induced by wetting. An appropriate description of the behavior of unsaturated soils must incorporate these fundamental effects of wetting on strength and deformation. The experimental evidence in terms of stiffness, compressibility, and strength is presented and discussed.
Francesca Casini

Chapter 15. Beyond Hydrocarbon Extraction: Enhanced Geothermal Systems

There are many forms of energy that exist subsurface. Mining typically extracts minerals that are energy rich and processes them to produce electricity. The oil and gas industry extracts hydrocarbons with high energy content that are suitable for energy production. This chapter illustrates the concept of “heat mining” that is a form of mining but has not caught much attention. This term “heat mining” was originally used to describe a general concept of mining heat from deep granitic rocks by injecting cold water and recovering it as steam or water/steam mixture to produce electricity. Beginning with the Fenton Hill Hot Dry Rock project developed by Los Alamos National Laboratory in 1971, there is a long history of development of different types of heat mining projects in Japan, the UK, China, Germany, France, Iceland, and Hungary. This chapter presents a simple conceptual model of a doublet reservoir that can be developed in a sedimentary basin at a depth below where the conventional hydrocarbon resources can be found. In addition, as we move forward with the development of the original heat mining concept from granitic rocks, it is important to understand the consequences of long-term heat extraction. Developing an enhanced geothermal system or engineered geothermal system (EGS) is a complex process and is dependent on a range of geological and operating variables. Stress distribution and re-distribution in and around EGS during the different phases of development may have a significant impact on the reservoir itself as well as surrounding rock masses. Thus, the second part of this paper addresses issues associated with stress redistribution during and after the working cycle of EGS and gives insights in understanding the behavior of stress redistribution in and around basement rock. As the basement rock is thermo-elastically connected to the country rock, newly generated stresses interact with the existing in situ stresses under prevailing conditions of geological, design, and operating variables. Inability to predict the timing and the degree of impact suggests a need of a consorted effort of investigations between oil/gas, mining and geothermal industry, and academic disciplines.
Masami Nakagawa, Kamran Jahan Bakhsh, Mahmood Arshad

Chapter 16. Some Economic Issues in the Exploration for Oil and Gas

In this chapter I present a simple economic model of exploration, and then discuss some predictions stemming from the model. I also describe some empirical phenomena relevant to exploration: trends in the probability of dry holes, the relation between oil prices and exploratory drilling, and developments in the deep water Gulf of Mexico.
Charles F. Mason

Erratum to: Nano-Scale Characterization of Organic-Rich Shale via Indentation Methods

Ange-Therese Akono, Pooyan Kabir


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