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Perforation is the key to the successful implementation of hydraulic fracturing, and the study of perforation parameters is of great significance for reservoir reconstruction and oil and gas exploitation. A finite element model is established to simulate multi-hole fractures' initiation and propagation based on the global embedded cohesive zone model. In the model, the reservoir is considered a dense, low-permeability porous elastic medium, wherein the coupling effect of fluid and geomechanics during fracturing is considered. The KGD analytical solution is consistent with the simulation results, verifying the cohesive zone model's accuracy. The results show that there are four competitive modes for multi-hole crack initiation. Firstly, the cracks open initially and remain open; secondly, the hole is open but not cracked; thirdly, the initial initiation extends and then closes; finally, the initial crack did not start in the late crack. With the increase of perforation density, the perforation initiation rate and average fracture pressure gradually decrease, and the fracture complexity in the near-wellbore area increases. With the increase of displacement and viscosity, the initial crack rate, the number of main cracks and microcracks formed in the hole tend to increase, while horizontal stress difference has an inversely proportional trend. In the presence of multiple perforating holes, the crack propagation presents a change from complex to simple, and the number of cracks presents a change from more to less. The expansion mode is formed with 2–4 main cracks and micro-cracks as auxiliary.

Network traffic flows contain a large number of correlated and redundant features that significantly degrade the performance of data-driven network anomaly detection. In this paper, we propose a novel clustering and ranking-based feature selection scheme, termed as CBFS, to reduce redundant features in network traffic, which can greatly improve the efficiency and accuracy of feature-based network anomaly detection. Our proposed CBFS scheme first calculates the distance between feature vectors, merges these feature vectors into different clusters, and selects the center of each cluster as a representative feature vector. The proposed CBFS scheme then integrates the information gain and gain rate of features to further streamline the number of features on the basis of clustering generation. Finally, the proposed CBFS scheme applies the decision-tree-based classifier to the generated subset of features so that the abnormal traffic flows are detected. The experimental results show that our proposed CBFS scheme is effective in reducing feature dimensions across different datasets. The proposed CBFS scheme can achieve feature reduction rates of 20% to 70%, and cost-performance of up to 70% as compared to benchmarking methods.

Among investigations on the mechanics of energy accumulation via well shut-in to increase oil production, reservoir imbibition is deemed effective. However, another element, i.e., the coupling effect of fluid flow and geomechanics has always been underrated in production. Hence, this is discussed herein based on seepage mechanics, elastic mechanics, and Biot pore elastic theory. Further, an integral mechanical coupling numerical model is established from staged fracturing on a horizontal well to analyze well shut-in and production, to simulate stress variation during the shut-in period and the impact of shut-in time on oil production. The model considers the coupling effect of oil and water flow, and geomechanics on the stress distribution of reservoir adjacent to hydraulic cracks during fracturing, well shut-in, and production. From the study of reservoir stress and physical parameters in different shut-down times, it is found that reservoir stress and physical parameters demonstrate some regular changes. The pore pressure and saturation demonstrate pressure diffusion and oil phase saturation recovery with increasing well shut-in time. Owing to pressure diffusion, horizontal maximum principal stress, and horizontal minimum principal stress, the shear stress and stress difference demonstrate high complexity. Meanwhile, permeability and porosity exhibit a complex distribution subject to effective stress; the characteristic parameters of reservoir rock based on construction parameters (total injection volume, injection rate, and shut-in time) affect the subsequent production considerably. The correlation curves drawn upon a simulated experiment that reflect the construction parameters against cumulative oil production indicate that cumulative oil production is in direct proportion to shut-in time and in reverse proportion to injection rate. The optimum shut-in time is correlated positively with both the total injection volume and injection rate.

With the rapid increase in the exploitation of shale reservoirs in the Sichuan province of China, the demand for long horizontal wells for contacting reservoirs has also significantly expanded. With increasing horizontal sections, the coiled tubing (CT) penetration depth and efficiency of the surface weight transferred to the weight-on-bit (WOB) downhole are limited by the friction between the CT and wellbore. Plug milling with CT has become less efficient, and the final bridge plugs close to the bottom cannot be removed. Therefore, an experiment is conducted to study the effects of the pump rate on the vibration amplitude of the axial and radial directions, vibration frequency, and pressure difference. An improved tubing force analysis model is used to study the effect of a vibrator with different pump rates and friction coefficients on the CT surface weight, maximum set-down force, maximum pickup force, CT lockup depth, and maximum WOB of different plugs in well wx202 of the Wei Yuan shale block. The calculated data exhibit strong agreement with the real-time data collected from previous CT operations. The simulated results are used to solve the problems faced when milling the final four plugs at the end of a long horizontal section in well wx202. The results indicate that the amplitude variation in the radial vibration at both ends of the hydraulic oscillator is greater than that in the axial direction under the same pump rate. The optimized flow rate for the vibrator is 8.33 L/s. The use of a vibrator can greatly reduce the friction and transfer that are sufficient for a WOB downhole.

This paper presents our vision of on-the-wall tangible interaction. We envision a future where tangible interaction can be extended from conventional horizontal surfaces to vertical surfaces; indoor vertical areas such as walls, windows, and ceilings can be used for dynamic and direct physical manipulation. We first discuss the unique properties that vertical surfaces may offer for tangible interaction and the interaction scenarios they imbue. We then propose two potential paths for realizing on-the-wall interaction and the technical challenges we face. We follow with one prototype called Climbot. We showcase how Climbot can be used as an on-the-wall tangible user interface for dynamic lighting and as a wall switch controller. We conclude with a discussion of future work.

We propose Auth+Track, a novel authentication model that aims to reduce redundant authentication in everyday smartphone usage. By sparse authentication and continuous tracking of the user’s status, Auth+Track eliminates the “gap” authentication between fragmented sessions and enables “Authentication Free when User is Around”. To instantiate the Auth+Track model, we present PanoTrack, a prototype that integrates body and near field hand information for user tracking. We install a fisheye camera on the top of the phone to achieve a panoramic vision that can capture both user’s body and on-screen hands. Based on the captured video stream, we develop an algorithm to extract 1) features for user tracking, including body keypoints and their temporal and spatial association, near field hand status, and 2) features for user identity assignment. The results of our user studies validate the feasibility of PanoTrack and demonstrate that Auth+Track not only improves the authentication efficiency but also enhances user experiences with better usability.

The fracture propagation in hydraulic fracturing is described as a nonlinear problem dynamic boundary. Due to the limitation of mesh refinement, it is difficult to obtain the real crack propagation path using conventional numerical methods. Meshless methods (MMs) are an effective method to eliminate the dependence on the computational grid in the simulation of fracture propagation. In this paper, a hydraulic fracture propagation model is established based on the element-free Galerkin (EFG) method by introducing jump and branch enrichment functions. Based on the proposed method, three types of fracturing technology are investigated. The results reveal that the stress interference between fractures has an important impact on the propagation path. For the codirectional fracturing simultaneously, fractures propagate in a repel direction. However, the new fracture is attracted and eventually trapped by the adjacent fracture in the sequential fracturing case. For the opposite simultaneous fracturing in multiwells, two fractures with a certain lateral spacing will deflect toward each other. The effect of stress shadow should be used rationally in the optimization of construction parameters; for the single well multistage fracturing, the stage spacing should be out of stress inversion area, while for the simultaneous fracturing of multiple wells, stress inversion zones should be used to maximize communication between natural fractures. Overall, this study establishes a novel and effective approach of using MM to simulate the propagation of hydraulic fractures, which can serve as a useful reference for understanding the mechanism of hydraulic fracture propagation under various conditions.

Based on fractal geometry theory, the Hagen–Poiseuille law, and the Langmuir adsorption law, this paper established a mathematical model of gas flow in nano-pores of shale, and deduced a new shale apparent permeability model. This model considers such flow mechanisms as pore size distribution, tortuosity, slippage effect, Knudsen diffusion, and surface extension of shale matrix. This model is closely related to the pore structure and size parameters of shale, and can better reflect the distribution characteristics of nano-pores in shale. The correctness of the model is verified by comparison with the classical experimental data. Finally, the influences of pressure, temperature, integral shape dimension of pore surface and tortuous fractal dimension on apparent permeability, slip flow, Knudsen diffusion and surface diffusion of shale gas transport mechanism on shale gas transport capacity are analyzed, and gas transport behaviors and rules in multi-scale shale pores are revealed. The proposed model is conducive to a more profound and clear understanding of the flow mechanism of shale gas nanopores.

Artificial intelligence (AI) is enabling the automated analysis of large amounts of image/video data, boosting the speed of multimedia data processing remarkably. Meanwhile, Image Quality Assessment (IQA) plays an important role in developing automatic analysis methods. To ensure the effectiveness of AI, images in multimedia applications should be considered for visual examination by both human and machine. Therefore, it is significant to understand the differences between human's and AI's perception of semantic distortion. However, little work has been done due to the lack of data from human on the semantic level. In this paper, we first propose a semantic database (SID) based on the surveillance scenarios, by collecting subjective average recognition rates of 3 semantic targets (face, pedestrian, license plate) with 3 types of distortion (JPEG Compression, BPG Compression, Motion Blur). Then, we present a detailed analysis of how human and AI perceive semantic distortion differently. Experimental results show that AI is stronger in tolerance to distortion than human beings on average, while weaker at generalization and stability. It is also implied in the experiments that existing IQA methods are not effective enough at judging the semantic distortion.

Perforation is the key to the successful implementation of hydraulic fracturing. The research on perforation mechanism is of great significance to perforation planning, completion design, hydraulic fracturing design, and proppant migration analysis. In this paper, a finite element model for simulating crack initiation and propagation in the presence of multiple perforations is established based on the global embedded cohesive zone model (CZM). The reservoir is considered as a dense, low-permeability porous elastic medium, and the coupling between fluid flow and geomechanics, as well as the back-stress effect, are considered. The Blanton's (1982) criteria were used to verify the accuracy of the global embedded CZM. Then five cases are used to discuss the effects of perforation density, horizontal stress difference (HSD) on fracture initiation, propagation, and fracture complexity. The results show: There are four competitive fracture initiation modes for multiple perforations: First, fracture initiation at an early stage and keeping on; Second, hole deformed but not cracked; Third, fracture initiation first and then close; Fourth, at the beginning, there is no fracture initiation, initiation later. With the increase of perforation density, affected by the decrease of flow distribution, increase of friction and stress interference, the initiation rate of perforations gradually decreases, and the fracture pressure shows a tendency of decreasing first and then increasing. When multiple perforations exist, the crack propagation changes from complex to simple, and the number of cracks changes from more to less. Finally, the expansion mode is formed with 2–3 main cracks as the main and micro cracks as the auxiliary. The increase of perforation density can increase the complexity of fractures around the wellbore, and is beneficial to the diversion of fractures and the expansion of the impact range of fractures. However, it can also cause distortion and deformation of the fracture wall and decrease of fracture opening near the wellbore, which can lead to difficulty in proppant migration. Under low HSD, under the influence of stress inversion, connected horizontal cracks are easy to form between holes, and the fractures are easier to turn and more complicated. Under high HSD, disconnected horizontal micro-cracks can be formed between holes, and the main fractures tend to develop into simple straight fractures. The results of our research have important practical guiding significance for the development of perforation plan, hydraulic fracturing design and proppant migration analysis.

Spontaneous imbibition behavior gained popularity several decades ago which led to widely exploited application in fractured reservoirs. Recently the imbibition behavior of unconventional reservoirs has attracted a good number of researchers and field engineers to pay attention and research more on how to enhance recovery through imbibition behavior. Despite the numerous studies that have been conducted in this area, it is still controversial whether spontaneous imbibition behavior is applicable on reservoir stimulation especially for shale reservoir. In this paper, the recent works on the spontaneous imbibition behavior in unconventional reservoirs particularly for shale has been reviewed. This paper is divided into four main sections, the first section presents the review of the research progress in wettability, the imbibition scale model, and the pore-throat structure with regard to the capillary force and its related influencing factors. Moreover, the shortcomings of current research methods are presented. The second section involves the water–rock interaction examination including the ion exchange between the fracture fluid and reservoir as well as the evolution of the rock physical properties during well shut-in. The third section presents the review of the numerical simulation methods that have been used to study imbibition in the recent years focusing on the flow characteristics at the micro scale. In the final section, the future research directions from the current conducted researches have been suggested. Our research proposes that the thermal-hydro-mechanical-chemistry multi-field coupling effect should be considered in numerical simulations. It can provide a basis and reference for quantifying the effect of imbibition stimulation during the shut-in time.

Non-planar fractures often occur in directional well fracturing and old well refracturing, which has great influence on fracture parameters and well production. To better understand the mechanism of non-planar fracture propagation, the mathematical model of non-plane fracture propagation is established based on the coupling of rock deformation and fluid flow in fracture. The coupled model is solved by a combination of the displacement discontinuity method and finite difference method, and the whole numerical calculations are carried out by MATLAB-developed program. The accuracy of the model is verified by comparing the calculated results with existing models and published experiment. The effect of perforation angles, horizontal stress differences and injection rates on fracture extension trajectory, fracture width, injection pressure and pressure distribution in fracture is investigated. The model is also employed to explore the influence of injection rate and perforation angles on fracture propagation path in the Mahu block, Xinjiang province, China. The results indicate that the coupled model has a good agreement with the published experiment data. Fracture turning distance increases with the increasing injection rate. Perforating in the direction of maximum principal stress and low injection rate is beneficial to reduce the injection pressure. Fracture width near wellbore decreases with the increasing perforation angle and differential stress, and increase with the increasing injection rate. Injection pressure increases with the increasing perforation angle, differential stress and injection rate. In the non-planar fracture propagation process, fracture width first increases and then decreases gradually. With the growing differential stress, perforation angle and injection rate has less influence on fracture turning. In the formation with high differential stress, it is difficult to achieve long fracture turning distance.

The aim of the study involves examining the effect of heavy oil viscosity on fracture geometry in detail by establishing a heavy oil fracturing model and conventional fracturing model based on thermal–hydraulic–mechanical (THM) coupled theory, Walther viscosity model, and K–D–R temperature model. We consider viscosity and density within the heavy oil fracturing model as functions of pressure and temperature while that as constants within the conventional fracturing model. A heavy oil production well is set as an example to analyze the differences between the two models to account for the thermo-poro-elastic effect. The results show that temperature exhibits the most significant influence on the heavy oil viscosity while the influence of pressure is the least. In addition, a cooling area with a width of 0–1 m and varied length is generated near the fracture. The heavy oil viscosity increases sharply in this area, thereby indicating an area of viscosity increment. The heavy oil viscosity increases faster and is closer to wellbore, and a high viscosity increment reduces the mobility of the heavy oil and prevents the fracturing fluid from entering into the reservoir. The special viscosity distribution results in significant differences in pore pressure, oil saturation, and changing trends between these two models. In the heavy oil reservoir fracturing model, the thermal effect completely exceeds the influence of pore elasticity, and the values of the fracture length, width, and static pressure exceed those calculated in the conventional fracturing model. Thus, a comparison of the measured values indicates that the results obtained by considering viscosity as a function of temperature and pressure are more accurate. Therefore, the results of this study are expected to provide good guidelines for the design of heavy oil fracturing.

Semantic information is important in video encryption. However, existing image quality assessment (IQA) methods, such as the peak signal to noise ratio (PSNR), are still widely applied to measure the encryption security. Generally, these traditional IQA methods aim to evaluate the image quality from the perspective of visual signal rather than semantic information. In this paper, we propose a novel semantic-level full-reference image quality assessment (FR-IQA) method named Semantic Distortion Measurement (SDM) to measure the degree of semantic distortion for video encryption. Then, based on a semantic saliency dataset, we verify that the proposed SDM method outperforms state-of-the-art algorithms. Furthermore, we construct a Region Of Semantic Saliency (ROSS) video encryption system to demonstrate the effectiveness of our proposed SDM method in the practical application.

Special nanoscale storage mechanisms and pore radii create complex shale gas transport mechanisms. Shale gas reservoir production performance evaluations are challenging due to difficulties associated with microcosmic flow mechanisms, such as Knudsen diffusion, surface diffusion, adsorption and desorption. A thorough understanding of the effects of these transport mechanisms on shale gas production can help to develop new and improved shale gas production prediction models. This paper derives a unified apparent permeability equation based on the Knudsen number and four flow regimes, incorporating viscous, slip, transition and free molecule flows. The new apparent-permeability model also considers the surface diffusion, adsorption layer and tortuous diffusion path. Fully coupled differential equations were developed for a hydraulic fracture and matrix system based on these microcosmic transport mechanisms and using the finite difference method. A sensitivity analysis was performed to investigate the impacts of several parameters on production, including the nanopore radii, Langmuir parameters and bottom-hole flow pressure. The simulation results demonstrate that the microcosmic flow mechanisms significantly impact shale gas production. Gas production increases as the Langmuir parameters increase, but the rate of the increase decreases over time. Knudsen diffusion and surface diffusion become more prominent as the pore radius and reservoir pressure decrease. The adsorption layer cannot be ignored at sufficiently small pore radii.

The ultra-low-permeability shale gas reservoir has a lot of well-developed natural fractures. It has been proven that hydraulic fracture growth pattern is usually a complex network fracture rather than conventional single planar fractures by micro-seismic monitoring, which can be explained as the shear and tensile failure of natural fractures or creation of new cracks due to the increase in reservoir pore pressure caused by fluid injection during the process of hydraulic fracturing. In order to simulate the network fracture growth, a mathematical model was established based on full tensor permeability, continuum method and fluid mass conservation equation. Firstly, the governing equation of fluid diffusivity based on permeability tensor was solved to obtain the reservoir pressure distribution. Then Mohr–Coulomb shear failure criterion and tensile failure criterion were used to decide whether the rock failed or not in any block on the basis of the calculated reservoir pressure. The grid-block permeability was modified according to the change of fracture aperture once any type of rock failure criterion was met within a grid block. Finally, the stimulated reservoir volume (SRV) zone was represented by an enhancement permeability zone. After calibrating the numerical solution of the model with the field micro-seismic information, a sensitivity study was performed to analyze the effects of some factors including initial reservoir pressure, injection fluid volume, natural fracture azimuth angle and horizontal stress difference on the SRV (shape, size, bandwidth and length). The results show that the SRV size increases with the increasing initial pore reservoir and injection fluid volume, but decreases with the increase in the horizontal principal stress difference and natural fracture azimuth angle. The SRV shape is always similar for different initial pore reservoir and injection fluid volume. The SRV is observed to become shorter in length and wider in bandwidth with the decrease in natural fracture azimuth angle and horizontal principal stress difference.

Multistage fracturing technology is critical to coalbed methane (CBM) production from horizontal wells. Further, optimizing the fracture parameters has a crucial influence on the stimulated reservoir volume and gas production. To investigate fracture parameter optimization, a stress interference model, hydraulic fracture propagation model, and a CBM productivity model are proposed. The effects of crack length and spacing for one to three fractures on the induced stress are calculated by implementing a static analysis MATLAB-developed program. The extended finite-element method is used to study the mechanism of simultaneous fracturing and sequential fracturing. In addition, the influences of cluster spacing and stage spacing on the stress field, formation pressure, fracture geometry, gas production, and reservoir pressure drop are comprehensively investigated by using Abaqus and COMET3 software. The simulation results indicate that with multiple fractures, fracture spacing of 80 m and fracture length of 160 m are conducive for dilating the secondary fracture system and producing a broader contact area in the coal seam. Moreover, an optimal cluster spacing of 15 m, a fracture interval of 80 m, and two cluster numbers per stage are better at forming a uniform fracture geometry with low injection pressure; within a given horizontal well section length of 500 m, fracture parameters with cluster spacing of 30 m, fracture spacing of 80 m, and two clusters per stage offer the best production performance. The simulation results are applied in well TP-07, and microseismic monitoring was conducted to monitor fracture propagation. The microseismic monitoring results are consistent with the numerical simulation.