Summary In this paper, an integrated discrete-element-method (DEM)/computational-fluid-dynamics (CFD) numerical-modeling work flow is developed to model proppant embedment and fracture conductivity after hydraulic fracturing. Proppant with diameter from 0.15 to 0.83 mm was modeled as a frictional particle assembly, whereas shale formation was modeled as a bonded particle assembly by using the bonded-particle model in PFC3D (Itasca Consulting Group 2010). The mechanical interaction between proppant pack and shale formation during the process of fracture closing was first modeled with DEM. Then, fracture conductivity after the fracture closing was evaluated by modeling fluid flow through the proppant pack by use of DEM coupled with CFD. The numerical model was verified by laboratory fracture-conductivity experiment results and the Kozeny-Carman equation. The simulation results show that the fracture conductivity increases with the increase of proppant concentration or proppant size, and decreases with the increase of fracture-closing stress or degree of shale hydration; shale-hydration effect was confirmed to be the main reason for the large amount of proppant embedment.

Optical microcapsules encapsulating optical materials inside a symmetric spherical confinement are significant elements for the construction of optical units and the integration of optical arrays. However, the multiple stimuli-responsive characteristic of optical microcapsules still remains a challenge due to the insuperable physical barrier between the optical material core and the outside shell and the lack of effective mechanisms to trigger the dynamic switch of the encapsulated optical materials. Inspired by the dual-mode optical modulation of chameleon skins, a novel biomimetic binary optical microcapsule that combines the visible light reflection of chiral nematic liquid crystals and photoluminescence emission of rare-earth complexes is assembled by microfluidic emulsification and interfacial polymerization. The reflected color, fluorescent intensity, and size of the optical microcapsules are facilely controlled in the microfluidic chip by adjusting the composition and flow rate of the injected fluids. Most importantly, the biomimetic binary optical microcapsules demonstrate three reversible responsive behaviors, thermotropic reflection evolution, temperature-dependent fluorescence emission, and Fredericks electro-optical response. The bioinspired multiple stimuliresponsive optical microcapsules enabled by microfluidics provide a templated strategy to manufacture the next generation of intelligent optical units and to achieve the dynamic response of hybrid photonic devices.

In the fractured water drive reservoirs of China, because of the complex geologic conditions, almost all the active water invasions appear to be water breakthrough along fractures, especially along macrofractures. These seal the path of gas flowing, and make the remaining gas distributed in the pores into water blockage gas, and lead to gas and water interactive distribution in the fractured gas reservoir. These complicated fractured systems usually generate some abnormal flowing phenomena such as the crestal well produces water while the downdip well in the same gas reservoir produces gas, or the same gas well produces water intermittently. It is very difficult to explain these phenomena using existing fracture models because of simply handling macrofractures and not considering nonlinear flowing in the macrofractures and the low permeability matrix. Therefore, a nonlinear combined-flowing multimedia simulation model is successfully developed in this paper by introducing the equations of macrofractures and considering nonlinear flowing in the macrofractures and the matrix. Next, we applied this model to actual fractured bottom water gas fields. And we have completed sensitivity studies of production gas by water drainage in fractured gas reservoirs and calculated the effect of different water drainage intensity and ways on actual gas production using this model. This model has been extensively used to predict the production performance in various fractured gas fields and proven to be reliable. Introduction Simulation of multiphase flow in heterogeneous two porosity reservoirs such as naturally fractured system is a difficult problem from both a reservoir description and a numerical standpoint. The reservoir is represented by two collocated continuums, i.e. a fracture continuum and a matrix continuum. The fracture continuum has high permeability and low storage volume while the matrix continuum has low permeability and high storage volume. Simulation of naturally fractured reservoirs has received much interest since the extension of Warren and Root's1 model to multiphase systems by Kazemi et al2–4. Further developments were made by Iffly et al5., Yamamoto et al6., Kleppe and Morse7, Rossen8, and Thomas et al9., and others. These models include laboratory investigations of oil and gas recovery from individual matrix blocks and simulation of single- and multiphase flow in fractured reservoirs. Most of the multiphase models account emphatically for the viscous, gravity and capillary forces, or several of them. In these models, usually the matrix blocks are assumed isolated block surrounded by a continuous fracture medium. The matrix blocks act as sources or sinks to the fractures, which are the main flow channel. This kind is called dual-porosity model. The other is dual-permeability model, also considering the matrix to matrix flow. In recent years, the accurate modelling of matrix-fracture transfer has been the most important aspect of the simulation of naturally fractured reservoirs. Numerous papers have appeared in the literature11–15 discussing various approaches for improving the handling of the transfer in black-oil simulation where the interaction between capillary and gravity forces plays an important role. The main deficiency of the original dual-porosity was the treatment of the gravity terms in the exchange terms. Several approaches have been proposed to account for gravity effects to enhance the dual-porosity concept. A summary of the various approaches can be found in Gilman and Kazemi3 and Fung and Collins10–12. It has received more and more attention.

Abstract. The characteristics of hole and seepage of carbonate rocks depend on the structural components of carbonate rocks and the combination relationship with these structural components under multi-scale. The quality of filling in reservoir fracture is an important part of fracture description. In this paper, the method of microscopic infrared spectral imaging was used, and the spectra cubic database was established by means of spectral imaging experiment. Each single band image which characterizes the related substances was extracted and the microcosmic characters of the filling in carbonate reservoirs fracture from Wumishan formation in Renqiu oilfield were studied. The spatial distribution maps of different chemical composition and groups in the core sample were obtained. The distribution of different hydrocarbon in the fracture of the reservoir and the connectivity of the pores etc. were better revealed