Dynamic Modeling of Pulse-like Earthquake and Ground Motion

Growth of major populated cities near active faults (e.g., Los Angeles and San Francisco in USA, Tokyo and Osaka in Japan) has significantly elevated the seismic hazards. Understanding complex paradigm of near-fault ground motions is crucial in order to mitigate seismic hazards. Since the 1994 Mw 6.7 Northridge earthquake, there has been much discussion about the adequacy of building code and a term of “pulse”. The engineering effects of near-fault pulse-like ground motions were strikingly exhibited in the 1994 Northridge earthquake in which great seismic damage was attributed to the large impulsive ground shaking of this type. Such near-fault pulselike ground motions with high intensity and damage potentials are hypothetically associated to either pulse-like rupture on fault or the rupture directivity. These mechanisms will be introduced and studied.In Chapter 2, we study far-field effects of a self-healing pulse-like rupture mode with dynamic weakening. Pulse-like rupture leads to development of a second corner frequency, and the intermediate spectral slope is approximately 2 in most cases. The focal-sphere-averaged lower P and S wave corner frequencies are systematically higher for pulse-like models than crack models of comparable rupture velocity. The slip-weighted stress drop exceeds the moment-based stress drop for pulse-like ruptures, with the ratio ranging from about 1.3 to 1.65, while they are equal for the crack-like case. The transition from arresting- to growing-pulse rupture is accompanied by a large (factor of 1.6) increase in the radiation ratio. Thus, variations in rupture mode may account for the portion of the scatter in observational spectral estimates ofsource parameters.In Chapter 3, we confirm the pulse-like ground motion in the 2015 Nepal Gorkha earthquake is related to the causing fault geometry of the Main Himalayan Thrust (MHT). Our dynamic rupture simulations in an elastoplastic medium yield earthquake parameters comparable to those deduced from kinematic inversions, including seismic moment and rupture velocity. The simulations reproduce pulse-like behavior predicting pulse widths in agreement with those kinematic studies and supporting an interpretation in which the pulse-like time dependence of slip is principally controlled by rupture geometry and it is supported by near-field high-rate GPS recording at station KKN4.In Chapter 4, we will discuss the directivity-induced pulse-like ground motions and assess the extent to which plastic yielding, which is absent in standard kinematic models, may systematically affect the amplitude, frequency content, and distance scaling of directivity pulse. We perform some simple 2D kinematic and 3D spontaneous dynamic ruptures with and without plastic yielding on a planar and rough fault, and find that each of the four 3D models (flat and rough faults, with and without off-fault yielding), scaled to approximately magnitude 7, predicts a fault-normal pulse with characteristic behavior of observed pulses. Plastic yielding systematically reduces pulse amplitude and increases its dominant period, relative to models that neglect off-fault yielding. Yielding saturates near-fault peak ground velocity (PGV) with greater stress drops, alternatively interpreting observed magnitude saturation of PGV near a magnitude of 7, and provides physical supports of period-dependent distance taper and along-strike saturation of directivity-induced amplification, undermining the commonly used wedge-shaped directivity amplification

Microscopic remaining oil distribution and quantitative analysis of polymer flooding based on CT scanning

  To investigate the distribution characteristics of remaining oil after polymer flooding, the core samples of different stages of water flooding and polymer flooding were scanned and imaged based on CT scanning technology. The oil, water and rock were divided into three phases by image analysis method, and the corresponding digital cores were constructed. Through the qualitative and quantitative analysis of the two-dimensional image and three-dimensional structure at the same position, the quantitative characterization of the micro-residual oil distribution in different displacement stages is finally realized. The results show that, the polymer flooding can significantly improve the sweep efficiency, which can increase the oil recovery by 11.45% compared with water flooding. The remaining oil in the pore is mainly network and multiple, and mainly network distribution at the stage of water flooding. After adding polymer, the proportion of multiple remaining oil increases significantly and becomes the main occurrence state of remaining oil. Affected by Jamin effect, multiple residual oil in the pore is difficult to be recovered because it cannot pass through the throat. The radius of this part of remaining oil is usually 1.34-1.5 times that of the throat radius.Cited as: Wang, X., Yin, H., Zhao, X., Li, B., Yang, Y. Microscopic remaining oil distribution and quantitative analysis of polymer flooding based on CT scanning. Advances in Geo-Energy Research, 2019, 3(4): 448-456, doi:10.26804/ager.2019.04.1

Formation damage mechanism of a sandstone reservoir based on micro-computed tomography

Formation damage caused by well drilling, completion, oil testing, oil recovery, and stimulation seriously affects oil and gas production, the evaluation of which plays an important role in the process of oilfield development. Thus, it is necessary to study formation damage mechanism from micro scale. In this study, two sets of displacement experiments were conducted using two sandstone samples and two chemical reagents. Each set was divided into three processes: first formation water injection, reverse chemical reagents injection and second formation water injection. According to the results of displacement experiments, the permeability changes of two sandstone samples were analyzed and the formation damage rates of different experimental processes were calculated respectively. In addition, we analyzed the formation damage of the two samples from the macroscopic aspect according to the changes of inlet pressure curves. We compared the pore structure changes of sandstone samples at different experiment processes by computed tomography (CT) images, and found the particle migration phenomenon. Based on the core sensitive regions observed by CT images, the pore network models of the sensitive regions were extracted to quantitatively characterize the change of pore structure parameters (pore radius, throat radius, coordination number and tortuosity). Finally, we designed a two-dimensional microscopic seepage channel model according to the real core structure. The flow rule of solid particles in fluid was simulated by finite element method, and the reason of reservoir clogging was analyzed. Through this study, we found that the injection of chemical reagents increased the inlet pressure and led to the decrease of core permeabilities. There was a negative correlation between the export rate of particle migration and matrix deformation degree.Cited as: Wang, Z., Li, H., Lan, X., Wang, K., Yang, Y., Lisitsa, V. Formation damage mechanism of a sandstone reservoir based on micro-computed tomography. Advances in Geo-Energy Research, 2021, 5(1): 25-38, doi: 10.46690/ager.2021.01.0

Numerical simulation on structural safety and dynamic response of coal mine rescue ball with gas explosion load using Arbitrary Lagrangian-Eulerian (ALE) algorithm

Coal mine rescue devices, which can supply miners underground with fundamental shelters after gas explosion, are essential for safety production of coal mines. In this paper, a novel and composite structure-rescue antiknock ball for coal mine rescue is designed. Further, the structural safety and dynamic response under gas explosion of the antiknock ball is investigated by ALE algorithm. To achieve this goal, the ALE finite element method is described in dynamic form, and governing equations and the finite element expressions of the ALE algorithm are derived. 3 balls with different structures are designed and dynamic response analysis has been conducted in a semi-closed tunnel with explosive load of pre-mixed gas/air mixture by using ALE algorithm based on explicit nonlinear dynamic program LS-DYNA. Displacement field, stress field and energy transmission laws are analyzed and compared via theoretical calculations. Results show that the cabin door, emergency door and spherical shell are important components of the rescue ball. The 3# composite ball is the optimization structure that can delay the shock effect of the gas explosion load on a coal mine rescue system; the simulation results can provide reference data for coal mine rescue system design

Antithrombotic Therapy and Outcomes After ICD Implantation in Patients With Atrial Fibrillation and Coronary Artery Disease: An Analysis From the National Cardiovascular Data Registry (NCDR)®

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/112259/1/jah3831.pd

A multi-continuum model for simulating in-situ conversion process in low-medium maturity shale oil reservoir

In-situ conversion is proposed applicable for low-medium maturity shale oil reservoir. However, parallel chemical kinetic reactions and evolution of shale pores during in-situ conversion make the numerical simulation a challenging problem. Although shale is typical multiscale and heterogeneous media, few models in previous studies take the difference between organic and inorganic system into consideration, which cannot simulate fluid flow accurately. In this paper, a multi-continuum model, considering coupled thermal-reactive compositional flow, is developed to simulate in-situ conversion process in low-medium maturity shale oil reservoir. The reaction of kerogen and hydrocarbon is quantified using kinetic reaction model. The evolution of fluid composition and shale properties are also incorporated. The accuracy of multiple-interacting-continua model and compositional model are demonstrated by comparing with commercial software and analytical solution. Then, the typical hexagon vertical well heating pattern is simulated and the feasibility is evaluated from an economic aspect. Finally, a series of case studies are conducted to investigate the impact of operation parameters on shale oil production.Cited as: Wang, Z., Yao, J., Sun, H, Yan, X., Yang, Y. A multi-continuum model for simulating in-situ conversion process in low-medium maturity shale oil reservoir. Advances in Geo-Energy Research, 2021, 5(4): 456-464, doi: 10.46690/ager.2021.04.1

A Seismologically Consistent Surface Rupture Length Model for Unbounded and Width-Limited Event

A new surface-rupture-length ($SRL$) relationship as a function of magnitude ($\mathbf{M}$), fault thickness, and fault dip angle is presented in this paper. The objective of this study is to model the change in scaling between unbounded and width-limited ruptures. This is achieved through the use of seismological-theory-based relationships for the average displacement scaling and the aid of dynamic fault rupture simulations to constrain the rupture width scaling. The empirical dataset used in the development of this relationship is composed of $123$ events ranging from $\mathbf{M}~5$ to $8.1$ and $SRL~1.1$ to $432~km$. The dynamic rupture simulations dataset includes $554$ events ranging from $\mathbf{M}~4.9$ to $8.2$ and $SRL~1$ to $655~km$. For the average displacement ($\bar{D}$) scaling, three simple models and two composite models were evaluated. The simple average displacement models were: a square root of the rupture area ($\sqrt{A}$), a down-dip width ($W$), and a rupture length ($L$) proportional model. The two composite models followed a $\sqrt{A}$ scaling for unbounded ruptures and transitioned to $W$ and $L$ scaling for width-limited events, respectively. The empirical data favors a $\bar{D} \sim \sqrt{A}$ scaling for both unbounded and width-limited ruptures. The proposed model exhibits better predictive performance compared to linear $\log(SLR)\sim\mathbf{M}$ type models, especially in the large magnitude range, which is dominated by width-limited events. A comparison with existing $SRL$ models shows consistent scaling at different magnitude ranges that is believed to be the result of the different magnitude ranges in the empirical dataset of the published relationships.Comment: 21 pages, 11 figure

Inhibitory Effect of Curcumol on Jak2-STAT Signal Pathway Molecules of Fibroblast-Like Synoviocytes in Patients with Rheumatoid Arthritis

Hyperplasia of synovial membrane in rheumatoid arthritis (RA) is a critical pathological foundation for inducing articular injury. The janus kinase and signal transducer and activator of transcription (Jak-STAT) pathway plays a critical role in synovial membrane proliferation induced by platelet-derived growth factor (PDGF). To explore the anti-cell proliferation mechanism of curcumol, a pure monomer extracted from Chinese medical plant zedoary rhizome, the changes of Jak2-STAT1/3 signal pathway-related molecules in synoviocytes were observed in vitro. In this study, the fibroblast-like synoviocytes (FLS) in patients with RA were collected and cultured. The following parameters were measured: cell proliferation (WST-1 assay), cell cycles (fluorescence-activated cell sorting, FACS), STAT1 and STAT3 activities (electrophoretic mobility shift assay, EMSA), and the protein expressions of phosphorylated Jak2, STAT1, and STAT3 (Western blot). It was shown that curcumol could inhibit the RA-FLS proliferation and DNA synthesis induced by PDGF-BB in a dose-dependent manner in vitro. The transcription factors activities of STAT1 and STAT3 were obviously elevated after PDGF-BB stimulation (P < 0.05). Super-shift experiments identified the STAT1 or STAT3 proteins in the complex. Furthermore, the different concentration curcumol could downregulate the DNA binding activities of STAT1 and STAT3 (P < 0.05) and inhibit the phosphorylation of Jak2 while it had no effect on the protein expressions of STAT1 and STAT3. Positive correlations were found between changes of cell proliferation and DNA-binding activities of STAT1 and STAT3, respectively (P < 0.01). In conclusion, curcumol might suppress the FLS proliferation and DNA synthesis induced by PDGF-BB through attenuating Jak2 phosphorylation, downregulating STAT1 and STAT3 DNA-binding activities, which could provide theoretical foundation for clinical treatment of RA