A new approach for flow simulation in complex hydraulic fracture morphology and its application:Fracture connection element method

Efficient flow simulation and optimization methods of hydraulic fracture morphology in unconventional reservoirs are effective ways to enhance oil/gas recovery.Based on the connection element method(CEM)and distribution of stimulated reservoir volume,the complex hydraulic fracture morphology was accurately described using heterogeneous node connection system.Then a new fracture connection element method(FCEM)for fluid flow in stimulated unconventional reservoirs with complex hydraulic fracture morphology was proposed.In the proposed FCEM,the arrangement of dense nodes in the stimulated area and sparse nodes in the unstimulated area ensures the calculation accuracy and efficiency.The key parameter,transmissibility,was also modified according to the strong heterogeneity of stimulated reservoirs.The finite difference and semi-analytical tracking were used to accurately solve the pressure and saturation distribution between nodes.The FCEM is validated by comparing with traditional numerical simulation method,and the results show that the bottom hole pressure simulated by the FCEM is consistent with the results from traditional numerical simulation method,and the matching rate is larger than 95%.The proposed FCEM was also used in the optimization of fracturing parameters by coupling the hydraulic fracture propagation method and intelligent optimization algorithm.The integrated intelligent optimization approach for multi-parameters,such as perforation number,perforation location,and displacement in hydraulic fracturing is proposed.The proposed approach was applied in a shale gas reservoir,and the result shows that the optimized perforation location and morphology distribution are related to the distribution of porosity/permeability.When the perforation location and displacement are optimized with the same fracture number,NPV increases by 70.58%,which greatly improves the economic benefits of unconventional reservoirs.This work provides a new way for flow simulation and optimization of hydraulic fracture morphology of multi-fractured horizontal wells in unconventional reservoirs.

On Univalent Functions in Multiply Connected Domains

The present article is an account of results on univalent functions in multiply connected domains obtained by the author. It contains two rery simple proofs of Villat's formula; Schwarz's formula, Poisson's formula and Poisson-Jensen formula in multiply connected domains; the differentiability theorem with respect to the parameter of analytic function family containing one parametric variable on multiply connected domains; variation theorem and parametric representation theorem of univalent functions in multiply connected domains; the solution of an extremal problem of differentiable functionals.

Melamine/Stearic Acid Composite Nanowires and Vesicles with an Intercalated Nanostructure Prepared through NCCM Method

A solvent-non-solvent method invented in our laboratory for preparing non-covalently con- nected micelles （NCCM） was used to intercalate melamine （MA） molecules into stearic acid （SA） bilayers to form tile composite nanoparticles with an intercalated nanostructure in which a melamine bilayer is sandwiched between two stearic acid bilayers, NCCM method helps to sufficiently mix the two components in nanospace and meanwhile inhibits the strong tendency of self-crystallization of MA, leading to the intercalation. Although the nanopar- ticles have a regular inner structure, the primary MA/SA nanoparticles have an irregular morphology. Regular nanoparticles were obtained through annealing the suspension of the primary nanoparticles. Through annealing at different temperatures, the MA/SA compos- ite nanowires and vesicles with an intercalated structure were prepared respectively. It is proposed that the morphological change results from the change in the intercalated structure.

THREE-DIMENSIONAL FINITE ELEMENT DELAUNAY MESH GENERATION BY A PERFECTED NODE CONNECTION METHOD

How to automatically generate three-dimensional finite element Delaunay mesh by a peifected node connection method is introduced, where nodes are generated based on existing elements, instead of independence of node creation and elements generation in traditional node connection method. Therefore, Ihe the difficulty about how to automatically create nodes in the traditional method is overcome.

Localization of Oscillation Source in DC Distribution Network Based on Power Spectral Density

Direct current(DC)bus voltage stability is essential for the stable and reliable operation of a DC system.If an oscillation source can be quickly and accurately localized,the oscillation can be adequately eliminated.We propose a method based on the power spectral density for identifying the voltage oscillation source.Specifically,a DC distribution network model combined with the component connection method is developed,and the network is separated into multiple power modules.Compared with a conventional method,the proposed method does not require determining the model parameters of the entire power grid,which is typically challenging.Furthermore,combined with a novel judgment index,the oscillation source can be identified more intuitively and clearly to enhance the applicability to real power grids.The performance of the proposed method has been evaluated using the MATLAB/Simulink software and PLECS RT Box experimental platform.The simulation and experimental results verify that the proposed method can accurately identify oscillation sources in a DC distribution network.

An innovative steel-concrete joint for integral abutment bridges

Integral abutment bridges are becoming rather common, due to the durability problems of bearings and expansion joints. At the same time, among short- and medium-span bridges, multi-beam steel-concrete composite deck with hot-rolled girder is an economical and interesting alternative to traditional pre-stressed concrete solutions. The two concepts can be linked together to design integral steel-concrete composite bridges with the benefits of two typologies. The most critical aspect for these bridges is usually the joints between deck and piers or abutments. In this paper, an innovative beam-to-pier joint is proposed and a theoretical and experimental study is introduced and discussed. The analyzed connection is aimed at combining general ease of construction with a highly simplified assembly procedure and a good transmission of hogging and sagging moment at the supports in continuous beams. For this purpose, the traditional shear studs, used at the interface be- tween steel beam and upper concrete slab, are also used at the ends of steel profiles welded horizontally to the end plates. To better understand the behaviour of this kind of joints and the roles played by different components, three large-scale specimens were tested and an FE model was implemented. The theoretical and experimental results confirmed the po- tential of the proposed connection for practical applications and indicated the way to improve its structural behaviour.

ALTERING CONNECTIVITY WITH LARGE DEFORMATION MESH FOR LAGRANGIAN METHOD AND ITS APPLICATION IN MULTIPLE MATERIAL SIMULATION

A new approach for treating the mesh with Lagrangian scheme of finite volume method is presented. It has been proved that classical Lagrangian method is difficult to cope with large deformation in tracking material particles due to severe distortion of cells, and the changing connectivity of the mesh seems especially attractive for solving such issues. The mesh with large deformation based on computational geometry is optimized by using new method. This paper develops a processing system for arbitrary polygonal unstructured grid,the intelligent variable grid neighborhood technologies is utilized to improve the quality of mesh in calculation process, and arbitrary polygonal mesh is used in the Lagrangian finite volume scheme. The performance of the new method is demonstrated through series of numerical examples, and the simulation capability is efficiently presented in coping with the systems with large deformations.