Geomechanical Controls on Frac-Hits

The communication among the horizontal wells or "frac-hits" issue have been reported in several field observations. These observations show that the "infill" well fractures could have a tendency to propagate towards the "parent" well depending on reservoir in-situ conditions and operational parameters. Drilling the horizontal wells in a "staggered" layout with both horizontal and vertical offset could be a mitigation strategy to prevent the "frac-hits" issue. In this study, we present a detailed geomechanical modeling and analysis of the proposed solution. For numerical modeling, we used our state-of-the-art fully coupled poroelastic model "GeoFrac-3D" which is based on the boundary element method for the rock matrix deformation/fracture propagation and the finite element method for the fracture fluid flow. The "GeoFrac-3D" simulator fully couples pore pressure to stresses and allows for dynamic modeling of production/injection and fracture propagation. The simulation results demonstrate that production from a "parent’ well causes a non-uniform reduction of the reservoir pore pressure around the production fractures, resulting in an anisotropic decrease of the reservoir total stresses, which could affect fracture propagation from the "infill" wells. We examine the optimal orientation and position of the "infill" well based on the numerical analysis to reduce the "frac-hits" issue in the horizontal well refracturing. The posibility of "frac-hits" can be reduced by optimizing the direction and locations of the "infill" wells, as well as re-pressurizing the "parent" well. The results suggest that arranging the horizontal wells in a "staggered" or "wine rack" arrangement decreases direct well interference and could increase the drainage volume.

Acrylonitrile-Styrene-Acrylate Particles with Different Microstructure for Improving the Toughness of Poly(styrene-co-acrylonitrile) Resin

Herein, acrylonitrile-styrene-acrylate copolymer (ASA) particles with different microstructure were synthesized by emulsion polymerization and then used for toughening poly(styrene-co-acrylonitrile) (SAN) resin. The structure of ASA particles was confirmed by FTIR. TEM results demonstrated that the particles with different morphologies of multilobe shape, complete core-shell and dumbbell shape were obtained depending on the cross-linker amount. It was found that the toughening efficiency reached the highest when the ASA particles had complete core-shell structure and the shell composition was close to that of the SAN matrix. It was ascribed to the fact that the complete shell layer and similar shell composition provided sufficient interfacial adhesion and transferred stress to induce larger matrix deformation, so that the notched impact strength increased accordingly. Moreover, the notched impact strength of SAN/ASA blend was improved without significantly sacrificing tensile strength when adding 30 wt% ASA particles with the size of around 400 nm. SEM results of the impact-fractured surfaces revealed that irregular fluctuation and numerous microvoids occurred. It was deduced that the toughening mechanism was attributed to the crazings and cavitation of particles. Therefore, this study paved a way of toughening the resin by adjusting the microstructure of the particles including morphology, composition, and size.

Novel assessment and prediction method for vessel traffic risk degree

To assess the current risk degree and predict the future risk degree of vessel traffic, a novel method is put forward in this study. Different from the existing literature, the available evidence of vessel traffic is directly transformed into the weighted basic probabilistic assignment (BPA) based on the optimal solution to the intersection of fuzzy membership functions in the framework of D-S evidence theory. The matrix deformation algorithm towards the combination rule makes the time complexity low in the process of the risk degree assessment. With respect to the risk degree prediction, the required Sigma points are effectively extracted. We derive the adaptive filtering gain that is suitable for the rapidly changing BPA. Finally, the experiments of vessel traffic in the Dalin Bay are made to indicate performance of the proposed method.

A MULTI-FIELD COUPLED SEEPAGE MODEL FOR COAL SEAM WITH FRACTURES OF POWER LAW LENGTH DISTRIBUTIONS

In the process of gas mining, the fracture distribution with power law length and the pore structure with adsorption effect have an important influence on the coal seam permeability. In recent years, the research on the internal structure of coal seam and the fluid flow mechanism has attracted a large number of researchers. In this paper, by considering the coal matrix deformation caused by adsorption, a pore-fracture model coupled with the multi-field effects and with power law length distribution of fractures in coal seam is established based on the fractal theory for porous media. In this work, we study the influences of the power law exponent [Formula: see text] of fracture length and the ratio [Formula: see text] of the minimum to maximum fracture lengths on the permeability of coal seam and the evolution mechanism of permeability with the structural and mechanical parameters of coal seam. It is found that the permeability of coal seam is inversely proportional to [Formula: see text], directly proportional to [Formula: see text], and to Langmuir volume constant and Langmuir volume strain constant. Compared with other factors, the power law component [Formula: see text] of fractures has the most significant effect on the coal seam permeability.

The interplay between matrix deformation and the coordination of turning events governs directed neutrophil migration in 3D matrices

Neutrophils migrating through extravascular spaces must negotiate narrow matrix pores without losing directional movement. We investigated how chemotaxing neutrophils probe matrices and adjust their migration to collagen concentration ([col]) changes by tracking 20,000 cell trajectories and quantifying cell-generated 3D matrix deformations. In low-[col] matrices, neutrophils exerted large deformations and followed straight trajectories. As [col] increased, matrix deformations decreased, and neutrophils turned often to circumvent rather than remodel matrix pores. Inhibiting protrusive or contractile forces shifted this transition to lower [col], implying that mechanics play a crucial role in defining migratory strategies. To balance frequent turning and directional bias, neutrophils used matrix obstacles as pivoting points to steer toward the chemoattractant. The Actin Related Protein 2/3 complex coordinated successive turns, thus controlling deviations from chemotactic paths. These results offer an improved understanding of the mechanisms and molecular regulators used by neutrophils during chemotaxis in restrictive 3D environments.

Particle Retracking Algorithm Capable of Quantifying Large, Local Matrix Deformation for Traction Force Microscopy

Deformation measurement is a key process in traction force microscopy (TFM). Conventionally, particle image velocimetry (PIV) or correlation-based particle tracking velocimetry (cPTV) have been used for such a purpose. Using simulated bead images, we show that those methods fail to capture large displacement vectors and that it is due to a poor cross-correlation. Here, to redeem the potential large vectors, we propose a two-step deformation tracking algorithm that combines cPTV, which performs better for small displacements than PIV methods and a newly-designed retracking algorithm that exploits statistically confident vectors from the initial cPTV to guide the selection of correlation peak which are not necessarily the global maximum. As a result, the new method, named ‘cPTV-Retracking’, or cPTVR, was able to track more than 92% of large vectors whereas conventional methods could track 43-77% of those. Correspondingly, traction force reconstructed from cPTVR showed better recovery of large traction than the old methods. cPTVR applied on the experimental bead images has shown a better resolving power of the traction with different-sized cell-matrix adhesions than conventional methods. Altogether, cPTVR method enhances the accuracy of TFM in the case of large deformations present in soft substrates. We share this advance via our TFMPackage software.

A poroelasticity model for interstitial fluid flow and matrix deformation in a non-homogeneous solid tumor

This paper describes a small-strain poroelasticity model to examine the interstitial fluid pressure and matrix deformation in a non-homogeneous solid tumor consisting of an inner core with a reduced specific microvascular area encapsulated in an outer tissue shell with a regular specific microvascular area. A singular perturbation technique is employed to capture the transitional behavior at the interface between the inner core and outer shell under a cyclic microvascular pressure. The perturbation solution reveals the existence of two boundary layers: one at the interface between the inner core and outer shell, and the other at the tumor surface. The amplitude of the tumor interstitial fluid (TIF) pressure is at a lower constant level in the inner core and increases rapidly in the boundary layer at the interface between the inner core and outer shell to the pressure value of the corresponding homogeneous tumor with the outer shell properties. The radial strain undergoes dramatic changes in the boundary layers, and reaches the peak near the interface between the inner core and outer shell. The behavior of the effective stresses remains similar to that of the TIF pressure.

FITC-Dextran Release from Cell-Embedded Fibrin Hydrogels

Fibrin hydrogel is a central biological material in tissue engineering and drug delivery applications. As such, fibrin is typically combined with cells and biomolecules targeted to the regenerated tissue. Previous studies have analyzed the release of different molecules from fibrin hydrogels; however, the effect of embedded cells on the release profile has yet to be quantitatively explored. This study focused on the release of Fluorescein isothiocyanate (FITC)-dextran (FD) 250 kDa from fibrin hydrogels, populated with different concentrations of fibroblast or endothelial cells, during a 48-h observation period. The addition of cells to fibrin gels decreased the overall release by a small percentage (by 7–15% for fibroblasts and 6–8% for endothelial cells) relative to acellular gels. The release profile was shown to be modulated by various cellular activities, including gel degradation and physical obstruction to diffusion. Cell-generated forces and matrix deformation (i.e., densification and fiber alignment) were not found to significantly influence the release profiles. This knowledge is expected to improve fibrin integration in tissue engineering and drug delivery applications by enabling predictions and ways to modulate the release profiles of various biomolecules.

A Study on the Largest Hydraulic Fracturing Induced Earthquake in Canada: Numerical Modeling and Triggering Mechanism

ABSTRACT The Mw 4.6 earthquake that occurred on 17 August 2015 northwest of Fort St. John, British Columbia, is considered the largest hydraulic-fracturing-induced event in Canada, based on its spatiotemporal relationship with respect to nearby injection operations. There is a ∼5 day delay of this Mw 4.6 mainshock from the onset of fluid injection at the closest well pad (W1). In contrast, other two nearby injection wells (W2 and W3) have almost instantaneous seismic responses. In this study, we first take a forward numerical approach to investigate the causative mechanisms for the Mw 4.6 event. Specifically, three finite-element 3D poroelastic models of various permeability structures and presence or absence of hydraulic conduits are constructed, to calculate the coupled evolution of elastic stress and pore pressure caused by multistage fluid injections. Our simulation results suggest that pore pressure increase associated with the migration of injected fluid is required to accumulate sufficient stress perturbations to trigger this Mw 4.6 earthquake. In contrast, the elastic stress perturbation caused by rock matrix deformation alone is not the main cause. Furthermore, injection and seismicity at W1 may have altered the local stress field and brought local faults closer to failure at sites W2 and W3. This process could probably shorten the seismic response time and, thus, explain the observed simultaneous appearance of injection and induced seismicity at W2 and W3.