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In natural micro-nanoscale porous media, the movable fluid porosity can effectively represent storage and permeable properties, but various mineral compositions have complicated effects on it. Taking saline lacustrine shale as an example, this study researched the effects of mineral composition on movable fluid porosity, based on nuclear magnetic resonance (NMR), focused ion beam (FIB), and x-ray diffraction (XRD) experiments. The results show that movable fluid porosity exhibits a stronger dependence on porosity than movable fluid saturation does. Micropores (1000 nm) are mostly developed in silicate and gypsum minerals, and have a highly heterogeneous distribution. In contrast, carbonate intercrystalline pores are dominated by mesopores (100−1000 nm), and behave strongly heterogeneously. Many mesopores play a positive role in generating highly movable fluid porosity, but the development of micropores and macropores is not conducive to an increase in movable fluid porosity. Overall, a significant negative effect is observed between silicate mineral content and movable fluid porosity, and carbonate mineral content has a strong positive effect on movable fluid porosity, whereas movable fluid porosity exhibits a relatively small reduction with an increase in the gypsum.

Natural fractures, as the main flow channels and important storage spaces, have significant effects on the migration, distribution, and accumulation of tight oil. According to outcrop, core, formation micro image (FMI), cast-thin-section, and scanning electron microscopy data from the tight reservoir within the Permian Lucaogou Formation of the Junggar Basin, tectonic fractures are prevalent in this formation mainly on micro to large scale. There are two types of fractures worth noticing: diagenetic fractures and overpressure-related fractures, primarily at micro to medium scale. The diagenetic fractures consist of bedding fractures, stylolites, intragranular fractures, grain-boundary fractures, and diagenetic shrinkage fractures. Through FMI interpretation and Monte Carlo method evaluation, the macro-fractures could be considered as migration channels, and the micro-fractures as larger pore throats that function as storage spaces. The bedding fractures formed earlier than all tectonic fractures, while the overpressure-related fractures formed in the Middle and Late Jurassic. The bedding fractures and stylolites function as the primary channels for horizontal migration of tight oil. The tectonic fractures can provide vertical migration channels and reservoir spaces for tight oil, and readjust the tight oil distribution. The overpressure-related fractures are fully filled with calcite, and hence, have little effect on hydrocarbon migration and storage capacity. The data on tight oil production shows that the density and aperture of fractures jointly determine the productivity of a tight reservoir.

The study on mixed depositional reservoirs is widely attended in recent years. However, the mixed depositional reservoirs are generally characterized by complex pore structure, which is caused by strong heterogeneity, complex mineral compositions, and varying pore sizes, presenting a major challenge to describe the difference in pore structure between different samples. To address this challenge, the pore structure of mixed depositional reservoirs was evaluated by the fractal dimensions, and the influences of various mineral compositions on pore structure were analyzed. The fractal dimensions derived from NMR measurements or NMR logging data can be divided into two segments at T 2cutoff values, representing different fractal values and characteristics of pore structure. For the E 3 2 Formation in Yingxi field, the fractal dimension of movable fluid pores ranges from 2.628 to 2.917 (average 2.765), whereas the bound fluid pore systems are not following the fractal theory. Meanwhile, the fractal dimensions show a negative relationship with movable fluid porosity and permeability. The effects of various mineral compositions on fractal laws of the pore networks are different. Fractal dimension increases with the increases of clay mineral contents, and the decrease of dolomite content, while the effect of calcite content on fractal laws of the pore system is uncertain, and quartz from different genetic type represents different effect on fractal dimensions. This study is contributed for petroleum exploitation in mixed depositional reservoirs and shows that the fractal dimension can comprehensively indicate the complexity of the pore structure in mixed depositional reservoirs.

Hydrocarbon-bearing zone identification of tight reservoirs plays a crucial role in hydrocarbon exploration and development. However, tight carbonate reservoirs are generally characterized by complex lithology, low porosity, strong heterogeneity, and weak fluid logging responses, which present a major challenge to detect hydrocarbon-bearing zones using conventional methods. To address this challenge, this paper develops a new method defined as Rwa spectrum, taking advantage of the high vertical resolution and borehole coverage of the image logs. The Rwa spectra can be derived from the histogram distribution of the apparent resistivity values of formation water (Rwa) in a sliding window, combining the Simandoux equation and the triple-porosity model. The results show that a very broad Rwa spectrum with long tails corresponds to hydrocarbon-bearing zones, and the peak shape of it is flat. In contrast, the narrow Rwa spectrum corresponds to water-bearing zones, and the peak shape of it is a sharp spike. Furthermore, two Rwa spectrum parameters, namely AVERAGE (reflects the size of main peak values) and VARIANCE (reflects shape changes of the Rwa spectra) are defined to quantificationally detect hydrocarbon-bearing zones. For oil zones in Yingxi field, the AVERAGE had a value higher than 10 and the VARIANCE was higher than 10. And for water zones, the AVERAGE had a value lower than 4.5 and the VARIANCE was lower than 5. The resistivity values decrease linearly with the increase in pyrite content of the reservoirs of high pyrite content, which disturbs the response to resistivity values from different fluid types (oil, gas or water). Hence, this method is suitable for the formation of no or little pyrite contents (lower than 0.2), and the case where the salinity value of drilling mud is similar to that of formation water. Moreover, the method has been validated by production test data, providing unusual perspectives on the identification of fluid types in tight carbonate reservoirs.

The tight sandstones are characterized by low porosity, low permeability, complex pore structure and strong heterogeneity due to the extensive diagenetic modifications they experienced. Understanding of the impact of diagenetic alterations on reservoir quality is crucial to the hydrocarbon exploration and production in tight sandstones. Diagenetic facies, which is the comprehensive description of the diagenesis and diagenetic minerals, determines the formation and distribution of sweet spot. By correlating the diagenetic facies to well log responses, the subsurface distribution of porosity and permeability can be predicted. However, the prediction of diagenetic facies and reservoir quality via well logs in tight sandstones remains a challenging task. This paper critically reviews the impact of diagenesis and diagenetic minerals on reservoir quality in tight sandstones, and establishes a model for prediction of diagenetic facies via well logs, as assessed from peer reviewed papers in the literature as well as from the authors' personal experiences. This review begins with reviewing the impacts of compaction, cementation, dissolution and various types of diagenetic minerals on reservoir quality evolution. The definition and classification schemes of diagenetic facies are then discussed, and the reservoir quality as well as diagenetic evolution sequence of various diagenetic facies is summarized. The same diagenetic facies commonly display similar compositional and textural attributes, matrix and cement, as well as porosity systems. The well log responses (GR, AC, DEN, CNL, and RT) of various diagenetic facies are summarized by the calibration of log values with cores and related thin sections. By translating the diagenetic facies to conventional well logs, a predictable model, which can be used for subsurface reservoir quality prediction, is established. Then the theory of ECS logs is reviewed, and the application of ECS logs in diagenetic facies evaluation is discussed. At last, the quantitative characterization for various type and degree of diagenesis is reviewed, and the subsurface diagenetic facies is predicted by quantitative calculation of the compactional porosity loss, cementational porosity loss and dissolution porosity content via well logs. Correlating the diagenetic facies to well logs provides a powerful tool to predict the distribution of high quality reservoirs in tight sandstones. This review will provide insights into the reservoir quality evaluation and sweet spot prediction via well logs in tight sandstones.

Magnets have received broad attention for vibration energy harvesting due to noncontact, nonlinear forces that may be leveraged among harvesting system elements. Yet, opportunities to integrate multi-directional coupling among a nonlinear energy harvesting system subjected to impulsive excitations have not been scrutinized, despite widespread prevalence of such excitations. To characterize these potentials, this research investigates an energy harvesting system with magnetically induced nonlinearities and coupling effects under impulsive excitations. A system model is formulated and validated with experimental efforts to reconstruct static and dynamic properties of the system via simulations. Then, the model is harnessed to scrutinize dynamic response of the system when subjected to impulse conditions. This research reveals the clear impulse strength dependence and influence of asymmetries on total electrical energy capture and energy conversion efficiency that are tailored by magnetic force coupling. Asymmetry is found to promote greater impulse-to-electrical energy conversion when compared to the symmetric counterpart system and a benchmark nonlinear energy harvester. The roles of initial conditions exemplify how stored energy in an asymmetric energy harvesting system may be released during nonlinear impulsive response. These results provide insights about opportunities and challenges to incorporate magnetic coupling effects in nonlinear energy harvesting systems subjected to impulses.

Laboratory measurements include porosity, permeability, high pressure mercury intrusion (HPMI), nuclear magnetic resonance (NMR) measurements and microscopic analysis of thin sections and scanning electron microscope (SEM) were used to gain insight into the nature of the pore throat structure including pore geometry, pore size distribution and pore connectivity of Bashijiqike tight gas sandstones in Keshen 5, Keshen 6, Keshen 8, Keshen 9 and Keshen 13 Wellblock of Kuqa depression. The relationships between microscopic pore structure parameters and macroscopic petrophysical behaviors were investigated by regression analysis. The results show that various types of pores with wide ranges of pore radius are observed. The pore throats are very small (commonly rapex) controls permeability in tight gas sandstones. The NMR pore size distribution is broader than the HPMI pore throat distribution. In the NMR analysis, only the pore systems connected by the relatively large pore throats should be accounted as movable, and some portion of large pores, which are not connected by effective large pore throats, are not effectively movable. The effective movable porosity is calculated by excluding those pores restricted by the tiny pore throats. The content of effective movable porosity from NMR measurements shows good correlation relationship with the porosity connected by large pore throats in HPMI analysis. Three typical types of pore structures are recognized through thin section, SEM analysis combined with the capillary curve and NMR T2 spectrum, and the microscopic and macroscopic characteristics of the three pore structures are investigated. The pore structure were comprehensively evaluated and characterized by linking NMR T2 spectrum with HPMI analysis.

Permeability can effectively represent the ability of fluids to flow in porous media, and is a crucial physical parameter for the exploration of unconventional oil reservoirs. In low-permeable porous media, such as tight rocks, not all pores function as fluid flow channels; meanwhile, the pore surface tends to form unevenly adsorbed water lay. To date, the two phenomena above have not been considered in previous studies on permeability estimation models. In this study, a new fractal permeability model with variable pore sizes was proposed resulting in two advancements: (1) unevenly adsorbed water lay attached to pore surfaces was considered; and (2) instead of the total pore space, the movable fluid space obtained from nuclear magnetic resonance (NMR) experiments was used as the fluid flow channels in the porous media. Helium permeability data of 26 mixed rock samples from tight oil reservoirs were used to establish the accuracy of the proposed permeability model. The results of a sensitivity analysis show that high porosity and large pore diameters play a positive role in generating high permeability in porous media. The permeability decreased with an increase in the fractal dimension of the total pore space and the tortuosity fractal dimension of the total pore space and movable fluid space, whereas it first decreased and then increased as the fractal dimension of the movable fluid space increased. Furthermore, the proposed model indicates that the movable fluid space and unevenly adsorbed water lay greatly influence the fluid flow, specifically at lower permeabilities (K＜0.1 mD), while the influence of the unevenness of the adsorbed water lay on fluid flow is negligible at high permeabilities. Overall, the accuracy of the permeability estimation of the proposed model is reliable both in low-permeable and conventional porous media, and can be effectively applied to unconventional oil reservoirs.

Leveraging smooth nonlinearities in vibration energy harvesters has been shown to improve the potential for kinetic energy capture from the environment as a transduced, alternating flow of electric...

Recent reports exemplify both the potential and the concerns encountered in implementing post-buckled structures in diverse applications. By numerical and experimental methods, characterizations have provided useful insights on the dynamic sensitivities of such bi- or multistable structures subjected to either harmonic or stochastic excitations. Yet, the more realistic scenario of combined harmonic and stochastic loading has been not been closely examined so that such sensitivities might be fully illuminated. To provide a more complete understanding on the robustness and susceptibility of multistable structures to dynamic state transitions, this research establishes new analytical and experimental methods to quantify the likelihood of triggering transitions among dynamic regimes of an archetypal post-buckled structure as a result of combined harmonic and stochastic loading. It is discovered that persistent periodic snap-through dynamics are rapidly disabled by additional noise excitation when the harmonic excitation contribution occurs at frequencies close to the linearized resonance. The extra noise may also drastically compromise the integrity of small-amplitude periodic responses that occur at frequencies around one-half of the linearized resonance. Particular relative proportions of the noise standard deviation and harmonic excitation amplitude are uncovered that most readily compromise the robustness of a given steady-state dynamic regime. The analytical method also complements prior developments focused on stochastic resonance by uncovering the broader perspective of dynamic sensitivities of post-buckled structures under arbitrary combinations of harmonic and random driving loads.

We introduce a class of engineered metamaterials for the purpose of attenuating and trapping spectrally broadband vibration and acoustic energy. The physical phenomenon realized to effect such wideband energy dissipation performance is termed hyperdamping since it is the consequence of eliminating fundamental stiffness contributions within the material system so as to asymptotically enhance damping properties. A strategically sculpted elastomer topology is geometrically constrained and embedded in a poroelastic matrix to realize the metamaterial platform. Finite element model analyses guide design of the embedded hyperdamping inclusions while experimental studies on dynamic force transmissibility and acoustical absorption coefficient provide conclusive evidence that hyperdamping phenomena facilitate wideband energy dissipation in a lightweight material system that is not subject to the limitations of conventional resonance- or bandgap-based attenuation effects. The hyperdamping metamaterials thus meet the often conflicting performance requirements of real applications where broadband vibrations and noise must be abated using lightweight material solutions.

Fractures provide pore spaces for the preservation and migration of hydrocarbons and control the quality of dolomitic reservoirs. Textures caused by sedimentary and tectonic processes control the mechanical properties of dolostones and the development and distribution of fractures in them. An understanding of the influence of textures present in dolostones in the development of fractures is crucial. Therefore, massive micritic, brecciated, columnar stromatolitic, and siliceous dolostones and laminites present in the early Mesoproterozoic Wumishan Formation (between ca. 1.5 Ga and ca. 1.45 Ga) in the Jizhong Depression with varying internal textures were analyzed based on observations of outcrops, core, and microstructures to determine their influence on reservoir quality. The development characteristics of fractures in the dolostones were investigated, and their petrophysical properties were measured. Uniaxial and triaxial compression tests were utilized to explore the impacts of textures on the distribution patterns of fracture in the dolostones. The fracture density, porosity, and permeability are 5.4/m, 1.55%, and 17.10 mD in the homogeneous and massive micritic dolostone, with fracture oriented parallel or at an acute angle to the maximum principal stress direction. The fracture density, porosity, and permeability, respectively, are characterized by averages of 8.9/m, 6.39%, and 106.68 mD, and are significantly better in the brecciated dolostones, and the fractures develop along the preexisting weakly cemented planes between the brecciated textures. The fracture density of the siliceous dolostone is 9.8/m, and its porosity and permeability are 2.74% and 29.68 mD. The extension of high-angle fractures is usually restrained by the low-angle bedding fractures, and intensive microcracks are developed in the siliceous textures. The occurrence of algal laminae in dolostones increases the proportion of low-angle fractures; these fractures can extend along the maximum principal stress direction and rupture along the weak algal laminae. The fracture density and petrophysical properties of columnar stromatolitic dolostones (7.4/m, 4.39%, and 87.75 mD) are better than those of laminites (4.3/m, 1.21%, and 14.57 mD). Therefore, the formative environment of textures in dolostones controls the quality of the reservoirs in the Wumishan Formation. The reservoirs in brecciated dolostones that are located in structural highs and fracture zones and columnar stromatolitic dolostones deposited in high-energy intertidal to upper subtidal zones have the highest reservoir quality. The quality of the reservoirs in siliceous banded dolostones deposited in mid-energy intertidal zones is average, and that of massive micritic dolostones and laminites deposited in low-energy lower-subtidal zones is poor.

This work investigates a model design for lightweight, architected material inclusions that cultivate significant impact energy dissipation in structures. The inclusions are sustained near a critical point where damping is theoretically increased without bound. Using the principle, a material architecture and constraint mechanism are studied that exemplify the theory. Guided by a computational model and analysis, numerous specimens are fabricated and experimentation verifies that engineered material inclusions constrained nearer to critical points most effectively suppress structural dynamics following impact, minimize transmitted impulsive force, and better promote structural integrity. The concepts articulated here may find broad application for reusable, resilient protective structures.

In order to effectively take advantage of stiffness nonlinearities in vibration energy harvesters, the harvesters must be appropriately designed to ensure optimum direct current (DC) power generation. Yet, such optimization has only previously been investigated for alternating current (AC) power generation although most electronics demand DC power for their functioning. Moreover, real world excitations contain stochastic contributions combined with periodic components that challenges conventional approaches of investigation that only give attention to the harmonic excitation parts. To fill in the knowledge gap, this research undertakes comprehensive simulations to begin formulating conclusive understanding on the relationships between rectified power generation and nonlinear energy harvester system characteristics when the platforms are subjected to realistic combinations of harmonic and stochastic excitations. According to the simulation results, the rectified power demonstrates clear dependence on the load resistance in the unique limiting cases of complete or no stochastic excitation. When the excitation vibrations include both harmonic and stochastic components, the optimal resistance to maximize DC power exhibits a smoothly correlated but nonlinear change between the limiting case values of the resistance. The results of this investigation provide direct evidence of the intricate relationships among peak DC power, optimal resistive loads, and the nonlinear energy harvester design, and encourage continued study for direct analytical expressions that define such relationships.

Multistability is a characteristic that can introduce exceptional versatility in engineered structural systems. For such adaptive structures, multiple stable equilibria empower a means for large shape change, mechanical properties tuning, and dynamic response tailoring, all potentially free from the costs and complexity associated with sustained active controls and hardware. As a result, a comprehensive understanding on the sensitivities of transitioning between the stable equilibria of multistable structures is needed to effectively leverage the valuable adaptation mechanisms. Previous characterizations provided useful insights on the dynamic sensitivities to snap-through of bi- or multistable structures under either harmonic or stochastic excitations, but the more practical combination of harmonic and stochastic loading has not received close attention. To provide a more complete understanding on the robustness of adaptive, multistable structures under complex excitations, this research explores new methods to quantify the likelihood of triggering the dynamic transitions between stable equilibria in an archetypal, magnetoelastic, bistable cantilever beam due to combined harmonic and stochastic loading. The studies capture the myriad, steady-state dynamic response regimes and susceptibilities of the bistable architecture to suddenly transition to another stable equilibria, or back again, due to various levels of additive white noise in the total excitation spectra. It is discovered that when the harmonic excitation component occurs at a frequency close to the linearized resonance the additional noise excitation rapidly disables the persistent periodic snap-through dynamics, resulting in locally stable intrawell oscillation. On the other hand, the extra noise may drastically compromise the integrity of locally stable periodic responses that occur at frequencies around one-half of the linearized resonance. By addressing the previous unknowns regarding more realistic excitation spectra, these new insights and assessment methods provide important guidance towards effective implementation of bistable constituents in adaptive structures applications.

A critical transition occurs between pre- and post-buckled configurations of lightly-damped structures where the relative proportions of dissipative and elastic forces may reverse, theoretically giving rise to large effective damping properties. This paper describes computational and experimental studies that investigate such fundamental theory and principles. It is found that impact mitigation capabilities of elastic metamaterials are significantly enhanced by critical point constraints. The results of one-dimensional drop experiments reveal that constrained metamaterials reduce impact force and suppress rebound effects more dramatically than conventional damping methods, while constraints nearer to critical points magnify the advantages. When embedded into distributed structures as in conventional applications, it is found that constrained metamaterials provide superior impact mitigation capabilities than solid dampers applied at the same locations. All together, the results show that critical point con...