Mingzhen Wei

Image complexity and feature mining for steganalysis of least significant bit matching steganography

The information-hiding ratio is a well-known metric for evaluating steganalysis performance. In this paper, we introduce a new metric of image complexity to enhance the evaluation of steganalysis performance. In addition, we also present a scheme of steganalysis of least significant bit (LSB) matching steganography, based on feature mining and pattern recognition techniques. Compared to other well-known methods of steganalysis of LSB matching steganography, our method performs the best. Results also indicate that the significance of features and the detection performance depend not only on the information-hiding ratio, but also on the image complexity.

Preformed-Particle-Gel Extrusion Through Open Conduits During Conformance-Control Treatments

Millimeter-sized (10 um~mm) preformed particle gels (PPGs) have been used successfully as conformance control agents in more than 5,000 wells. They help to control both water and CO2 production through high-permeability streaks or conduits (large pore openings), which naturally exist or are aggravated either by mineral solutions or by a high injection pressure during the flooding process. This paper explores several factors that can have an important impact on the injectivity and plugging efficiency of PPGs in these conduits. Extensive experiments were conducted to examine the effect of the conduit’s opening size and the PPG strength on the ratio of the particle size to the opening diameter, injectivity index, resistance factor, and plugging efficiency. Five-foot tubes with four internal diameters were designed to emulate the opening conduits. Three pressure taps were mounted along the tubes to monitor PPG transport and plugging performance. The results show that weak gel has less injection pressure at a large particle opening ratio compared to strong gel. PPG strength impacted injectivity more significantly than did particle opening ratio. Resistance factor increased as the brine concentration and conduit opening size increased. PPGs can significantly reduce the permeability of an open conduit and their plugging efficiency depends highly on the particle strength and the conduit’s opening size. The particle size of PPG was reduced during their transport through conduits. Experimental results confirm that the size reduction was caused by both dehydration and breakdown. Based on the lab data, two mathematical models were developed to quantitatively calculate the resistance factor and the stable injection pressure as a function of the particle strength, particle opening ratio, and shear rate. This research provides significant insight into designing better millimeter-sized particle gel treatments intended for use in large openings, including open fractures, caves, worm holes, and conduits. Introduction Excess water production in oil fields is becoming a challenging economical and environmental problem as more reservoirs are maturing. An estimated average of three barrels of water are produced for each barrel of oil produced worldwide (Bailey et al., 2000). It is estimated that the total cost to separate, treat, and dispose of this water is approximately

Study on Gas Flow in Nano Pores of Shale Gas Reservoir

50 billion per year (Hill et al., 2012). Water can flow into the wellbore as a result of either near-wellbore problems or reservoirrelated problems (Seright et al., 2001). The mechanisms that contribute to this undesired water production must be fully understood before the appropriate treatment can be chosen. Water channeling, one of the primary reservoir conformance problems, is caused by reservoir heterogeneities that lead to the development of high-permeability streaks. These streaks include open fractures and fracture like features, such as caves, worm holes, and conduits (Smith et al, 2006). These highconductivity areas inside the reservoir only occupy a small fraction of the reservoir but will capture a significant portion of injected water. As a result, large amounts of oil remain unswept as a large water flood will bypass oil-rich unswept zones/areas. Gel treatments have been proven to be a cost-effective chemical conformance control technology to reduce the fluid flow in these large opening features. The application of these technologies can not only control water production but also significantly increase the oil production and extend the economic life of a reservoir. Traditionally, in-situ bulk gels have been used for this purpose. However, preformed particle gels recently have attracted much attention because they can solve some of the problems associated with in-situ gel systems, such as the dilution and dispersion of the gelant, chromatographic separation of the gelant solution, and so on. (Chauveteau et al., 2001, 2003; Coste et al., 2000; Bai et al., 2007a, 2007b).

Pressure transient and rate decline analysis for hydraulic fractured vertical wells with finite conductivity in shale gas reservoirs

Producing gas from shale gas reservoirs has played an increasingly important role in the volatile energy industry over recent years in North America for considerable volume of natural gas stored in the reservoirs. Unlike conventional gas reservoirs, the gas flow in shale reservoirs is a complex multi-scale flow process and has special flow mechanisms. Most importantly, the shale gas reservoir contains a large portion of nano pores. The study of flow in nano pores is essential for accurate shale gas numerical simulation. However, there is still not a comprehensive study in understanding how gas flows in nano pores. In this paper, based on the advection-diffusion model, we constructed a new mathematical model to characterize gas flow in nano pores. We derived a new apparent permeability expression based on advection and Knudsen diffusion. Acomprehensive coefficient in characterizing the flow process was proposed. Simulation results were verified against the experimental data for gas flow through nano membranes. By changing the comprehensive coefficient, we found the best candidate for the case of Argon with membrane pore diameter 235 nm. We verified the model using different gases (Oxygen, Argon) and different pore diameters (235 nm, 220 nm). The comparison shows that the new model matches the experimental data very closely. Additionally, we compared our results with experimental data, Knudsen/Hagen-Poiseuille analytical solution, and existing researcher’s work. The results show that this study yielded a more reliable solution. For shale gas simulation where gas flowing in nano pores plays a critical role, the results from this work will made the simulation more accurate and reliable. Introduction With the growing shortage of domestic and foreign energy, producing gas from shale strata has played an increasingly important role in the volatile energy industry over recent years in North America and is gradually becoming a key component in the world’s energy supply (Wang and Krupnick, 2013). A shale gas reservoir is characterized of an organic-rich deposition with extremely low matrix permeability and clusters of mineral-filled “natural” fractures (Fig.1). Through experiment analysis on 152 cores of nine reservoirs in North America, Javadpour (2009) found that the permeability of shale bedrock is mostly 54 nd and about 90% are less than 150 nd (Javadpour et al. 2007). Most of the pores’ diameter are concentrated in the range of 4 ~ 200 nm (10 m)(Curtis et al. 2010).

Transport of Nanogel through Porous Media and Its Resistance to Water Flow

Producing gas from shale strata has become an increasingly important factor to secure energy over recent years for the considerable volume of natural gas stored. Unlike conventional gas reservoirs, gas transport in shale reservoirs is a complex process. In the organic nano pores, slippage effect, gas diffusion along the wall, viscous flow due to pressure gradient, and desorption from Kerogen coexist; while in the micro fractures, there exist viscous flow and slippage. Hydraulic fracturing is commonly used to enhance the recovery from these ultra-tight gas reservoirs. It is important to clearly understand the effect of known mechanisms on shale gas reservoir performance. This article presents the pressure transient analysis (PTA) and rate decline analysis (RDA) on the hydraulic fractured vertical wells with finite conductivity in shale gas reservoirs considering multiple flow mechanisms including desorption, diffusive flow, Darcy flow and stress sensitivity. The PTA and RDA models were established firstly. Then, the source function, Laplace transform, and the numerical discrete methods were employed to solve the mathematical model. At last the type curves were plotted and different flow regimes were identified. The sensitivity of adsorption coefficient, storage capacity ratio, inter-porosity flow coefficient, fracture conductivity, fracture skin factor, and stress sensitivity were analyzed. This work is important to understand the transient pressure and rate decline behaviors of hydraulic fractured vertical wells with finite conductivity in shale gas reservoirs.

Detection of JPEG double compression and identification of smartphone image source and post-capture manipulation

The application of nanoparticles in enhanced oil recovery (EOR) continues to gain attention in the oil industry due to its apparent potential. However, previous studies have focused on the evaluation of stiff particles, such as silica and aluminum oxide. In this paper, we present our experimental results of deformable nanoparticle transport behavior through porous media. Nanogel particles with sizes ranging from 100-285 nm were used to represent deformable nanoparticles. Core flooding tests were run using sandstone cores with water permeabilities ranging from 42 to 1,038 mD. We investigated the effects of the permeability, particle concentration, particle deformability, and flow rate on the particle propagation, resistance factor, and residual resistance factor (permeability reduction factor). The results show that the resistance factor ranged from 5 to 14 for rocks with permeabilities higher than 311 mD, indicating that the nanoparticles were able to transport easily through these rocks. However, the resistance increased to 383 when the permeability was as low as 41.2 mD, indicating that the nanogel could not penetrate the rock easily. After placing the particles, brine was injected at different flow rates. The results indicate that the nanoparticles effectively reduced the permeability of the rocks with the original permeabilities of 143 to 555.4 mD, but the residual resistance factor of the high-permeability rock (1,038 mD) was relatively small, ranging from 2.67 to 4.39. The resistance factor and residual resistance factor increased with the particle concentration and decreased with the flow rate, and both factors can be well fitted using power law equations as a function of velocity. The nanogel adsorption layer thickness decreased with the shear rate. Introduction Water usually is injected into reservoirs as a secondary recovery method to maintain the reservoir pressure and displace oil. In wells nearing the end of their productive lives, about 2/3 of the oil remains underground, but water can constitute as much as 98% of the liquid brought to the surface. Enhanced oil recovery (EOR) methods often are implemented to increase oil recovery and reduce water production [Fletcher et al., 2010]. EOR methods improve oil recovery commonly through the following three primary mechanisms: (1) they mobilize residual oil by increasing the capillary number through interfacial tension (IFT) reduction and/or wettability modification methods, (2) they decrease the mobility ratio by adding polymer into the water to increase its viscosity, and (3) they improve conformance in heterogeneous reservoirs for better sweep efficiency by reducing the permeability of high-permeability zones or streaks [Hite et al., 2005; Lake et al., 1992; Thomas, 2005; Fletcher et al., 2010]. Many different chemical EOR materials exist that can be used to reduce permeability and improve conformance in reservoirs with high-permeability streaks and fractures, thus reducing water production. Gel treatment has been proven to be a cost-effective method for conformance control [Bai et al., 2013]. Several researchers have proposed methods that employ particle gels to homogenize reservoirs and control undesired water production (known as water shutoff). The particle gels include preformed particle gels (PPGs) [Bai et al., 2004], microgels [Chauveteau et al., 2000; Rousseau et al., 2005; Zaitoun et al., 2007], pH-sensitive gels [Al-anazi et al., 2002; Huh et al., 2005], and temperature-sensitive submicron-sized polymer (bright water) [Pritchett et al., 2003; Frampton et al., 2004]. These particles differ primarily in their size [Bai et al., 2013]. Several publications have noted that PPG, microgels, and submicron-sized particles have been implemented economically to decrease water production from mature oil fields. For example, PPGs have been applied successfully in more than 5,000 wells [Bai et al, 2013]. Microgels have been applied in 10 gas storage wells to decrease water production [Zaitoun, 2007]. Submicrogels (namely, bright water) have been used in more than 60 wells to divert in-depth fluid flow [Cheung, 2007, Mustoni 2010].

Decoupling the Stationary Navier-Stokes-Darcy System with the Beavers-Joseph-Saffman Interface Condition

Digital multimedia forensics is an emerging field that has important applications in law enforcement and protection of public safety and national security. In digital imaging, JPEG is the most popular lossy compression standard and JPEG images are ubiquitous. Today’s digital techniques make it easy to tamper JPEG images without leaving any visible clues. Furthermore, most image tampering involves JPEG double compression, it heightens the need for accurate analysis of JPEG double compression in image forensics.In this paper, to improve the detection of JPEG double compression, we transplant the neighboring joint density features, which were designed for JPEG steganalysis, and merge the joint density features with marginal density features in DCT domain as the detector for learning classifiers. Experimental results indicate that the proposed method improves the detection performance. We also study the relationship among compression factor, image complexity, and detection accuracy, which has not been comprehensively analyzed before. The results show that a complete evaluation of the detection performance of different algorithms should necessarily include image complexity as well as the double compression quality factor.In addition to JPEG double compression, the identification of image capture source is an interesting topic in image forensics. Mobile handsets are widely used for spontaneous photo capture because they are typically carried by their users at all times. In the imaging device market, smartphone adoption is currently exploding and megapixel smartphones pose a threat to the traditional digital cameras. While smartphone images are widely disseminated, the manipulation of images is also easily performed with various photo editing tools. Accordingly, the authentication of smartphone images and the identification of post-capture manipulation are of significant interest in digital forensics. Following the success of our previous work in JPEG double compression detection, we conducted a study to identify smartphone source and post-capture manipulation by utilizing marginal density and neighboring joint density features together. Experimental results show that our method is highly promising for identifying both smartphone source and manipulations.Finally, our study also indicates that applying unsupervised clustering and supervised classification together leads to improvement in identifying smartphone sources and manipulations and thus provides a means to address the complexity issue of the intentional post-capture manipulation on smartphone images.

A Dual-Porosity-Stokes Model and Finite Element Method for Coupling Dual-Porosity Flow and Free Flow

This paper proposes a domain decomposition method for the coupled stationary Navier-Stokes and Darcy equations with the Beavers-Joseph-Saffman interface condition in order to improve the efficiency of the finite element method. The physical interface conditions are directly utilized to construct the boundary conditions on the interface and then decouple the Navier-Stokes and Darcy equations. Newton iteration will be used to deal with the nonlinear systems. Numerical results are presented to illustrate the features of the proposed method.

Coreflooding and Pore-Scale Visualization of Foamed Gel Flowed in Porous Network Media

In this paper, we propose and numerically solve a new model considering confined flow in dual-porosity media coupled with free flow in embedded macrofractures and conduits. Such situation arises, for example, for fluid flows in hydraulic fractured tight/shale oil/gas reservoirs. The flow in dual-porosity media, which consists of both matrix and microfractures, is described by a dual-porosity model. And the flow in the macrofractures and conduits is governed by the Stokes equation. Then the two models are coupled through four physically valid interface conditions on the interface between dual-porosity media and macrofractures/conduits, which play a key role in a physically faithful simulation with high accuracy. All the four interface conditions are constructed based on fundamental properties of the traditional dual-porosity model and the well-known Stokes--Darcy model. The weak formulation is derived for the proposed model, and the well-posedness of the model is analyzed. A finite element semidiscretizati...

IMPROVING DATABASE QUALITY THROUGH ELIMINATING DUPLICATE RECORDS

To investigate the mechanisms of enhancing oil recovery and the flow behaviors of foamed gel in porous media, foamed gels with characteristics of excellent strength and viscosity were prepared with polymer, crosslinking agent, foam agent, and formation water. The breakthrough-vacuum method and a rotary viscometer were used to evaluate the strength and viscosity of foamed gel. Coreflooding and pore-level visualization experiments were performed in heterogeneous reservoir models. Laboratory results illustrate that high strength and viscosity of foamed gel can be prepared by 0.15% NJ-8, 0.2% polyacrylamide solution, and 1.5% foaming agent. The strength and viscosity of the foamed gel reached 0.06 MPa and 10,000 MPa · s, respectively. The results of coreflooding experiments in heterogeneous cores show that oil recovery can be improved by approximately 36.9% after injecting 0.3 pore volume of the foamed gel, and enhanced oil recovery is mainly attributed to the improving sweep efficiency of mid- to low-permeability layers. Images of visualization flooding demonstrate that foamed gel exhibits good oil resistance and elasticity when used with crude oil. Furthermore, the new amoeba effect, Jamin effect, fluid-diverting effect, and extruding effect between foamed gel and oil in porous media can enhance oil recovery by improving sweep efficiency. GRAPHICAL ABSTRACT