Microstructure and mechanical properties of Ni3Al intermetallics prepared by directional solidification electromagnetic cold crucible technique

The present work focused on the Ni_3Al-based alloy with a high melting point. The aim of the research is to study the effect of withdrawal rate on the microstructures and mechanical properties of directionally solidified Ni-25 Al alloy. Ni_3 Al intermetallics were prepared at different withdrawal rates by directional solidification(DS) in an electromagnetic cold crucible directional solidification furnace. The DS samples contain Ni_3 Al and Ni Al phases. The primary dendritic spacing(λ) decreases with the increasing of withdrawal rate(V), and the volume fraction of Ni Al phase increases as the withdrawal rate increases. Results of tensile tests show that ductility of DS samples is enhanced with a decrease in the withdrawal rate.

Prevention and forecasting of rock burst hazards in coal mines

Rock bursts signify extreme behavior in coal mine strata and severely threaten the safety of the lives of miners, as well as the effectiveness and productivity of miners. In our study, an elastic-plastic-brittle model for the deformation and failure of coal/rock was established through theoretical analyses, laboratory experiments and field testing, simulation and other means, which perfectly predict sudden and delayed rock bursts. Based on electromagnetic emission (EME), acoustic emission (AE) and microseism (MS) effects in the process from deformation until impact rupture of coal-rock combination samples, a multi-parameter identification of premonitory technology was formed, largely depending on these three forms of emission. Thus a system of classification for forecasting rock bursts in space and time was established. We have presented the intensity weakening theory for rock bursts and a strong-soft-strong (3S) structural model for controlling the impact on rock surrounding roadways, with the objective of laying a theoretical foundation and establishing references for parameters for the weakening control of rock bursts. For the purpose of prevention, key technical parameters of directional hydraulic fracturing are revealed. Based on these results, as well as those from deep-hole controlled blasting in coal seams and rock, integrated control techniques were established and anti-impact hydraulic props, suitable for roadways subject to hazards from rockbursts have also been developed. These technologies have been widely used in most coal mines in China, subject to these hazards and have achieved remarkable economic and social benefits.

Numerical simulation of high-resolution azimuthal resistivity laterolog response in fractured reservoirs

The high-resolution azimuthal resistivity laterolog response in a fractured formation was numerically simulated using a three-dimensional finite element method. Simulation results show that the azimuthal resistivity is determined by fracture dipping as well as dipping direction, while the amplitude differences between deep and shallow laterolog resistivities are mainly controlled by the former. A linear relationship exists between the corrected apparent conductivities and fracture aperture. With the same fracture aperture, the deep and shallow laterolog resistivities present small values with negative separations for low-angle fractures, while azimuthal resistivities have large variations with positive separations for high-angle fractures that intersect the borehole. For dipping fractures, the variation of the azimuthal resistivity becomes larger when the fracture aperture increases. In addition, for high-angle fractures far from the borehole, a negative separation between the deep and shallow resistivities exists when fracture aperture is large as well as high resistivity contrast exists between bedrock and fracture fluid. The decreasing amplitude of dual laterolog resistivity can indicate the aperture of low-angle fractures, and the variation of the deep azimuthal resistivity can give information of the aperture of high-angle fractures and their position relative to the borehole.

Study on linear shaped charge in penetrating rock

Based on the action mechanism of linear shaped charge（ LSC ）, penetration performance of LSC on rock was studied. The optimal standoff and the vertex angle of LSC were studied and determined by lab experiments. Through cutting sand-cement grout samples, the spacing interval of boreholes can approach 17.5 times of the bore-hole＇ s diameter, and the result of the directional expansion of crack is satisfactory. The result of field experiment indicates cutting effect is very good, the ruggedness in fracture plane is less than 50 mm, the rate of half-hole marks is nearly 100 % , and the crack inspection shows that there is no damage in the internal of the cutting part. All these suggest that the orientation fracture blasting with LSC is a good means in directional fracture controlled blasting and is worth popularizing widely.

Simulation of directional propagation of hydraulic fractures induced by slotting based on discrete element method

Hydraulic fracturing(HF)technology can safely and efficiently increase the permeability of coal seam,which is conducive to CBM exploration and prevent coal and gas outburst.However,conventional HF fractures tend to expand in the direction of maximum principal stress,which may be inconsistent with the direction of fracturing required by the project.Therefore,the increased direction of coal seam permeability is different from that expected.To solve these problems,PFC2D software simulation is used to study directional hydraulic fracturing(DHF),that is the combination of slotting and hydraulic fracturing.The effects of different slotting angles(θ),different horizontal stress difference coefficients(K)and different injection pressures on DHF fracture propagation are analyzed.The results show that the DHF method can overcome the dominant effect of initial in-situ stress on the propagation direction of hydraulic fractures and control the propagation of fractures along and perpendicular to the slotting direction when θ,K and liquid injection pressure are small.When the DHF fracture is connected with manual slotting,the pressure will shake violently,and the fracturing curve presents a multi-peak type.The increase and decrease of particle pressure around the fracturing hole reflect the process of pressure accumulation and fracture propagation at the fracture tip respectively.Compared with conventional HF,DHF can not only shorten the fracturing time but also make the fracture network more complex,which is more conducive to gas flow.Under the action of in-situ stress,the stress between slots will increase to exceed the maximum horizontal principal stress.Moreover,with the change in fracturing time,the local stress of the model will also change.Hydraulic fractures are always expanding to the area with large local stress.The research results could provide certain help for DHF theoretical research and engineering application.

Horizontal borehole azimuth optimization for enhanced stability and coal seam gas production

Horizontal boreholes have been widely used to extract natural gas from coal seams.However,these boreholes can encounter severe instability issues leading to production interruption.Optimizing drilling azimuth is a potential solution for enhancing borehole stability while considering gas production.In this work,we improved and implemented a dual-porosity,fully coupled geomechanical-hydraulic numerical model into COMSOL Multiphysics to investigate into this factor.The sophisticated numerical model incorporates various critical factors,including desorption-induced matrix shrinkage,stress-dependent anisotropic fracture permeability,and the interactions of gas flow and reservoir deformation in matrices and fractures.A suite of simulation scenarios(e.g.,varying coal strength)was carried out to quantify the impact of drilling azimuth on coal permeability evolution,cumulative gas production,and the borehole break-out width for Goonyella Middle Seam of Bowen Basin,Australia.The model was calibrated against both theoretical permeability values and field gas production data.Due to the lack of directly measured matrix permeability data,the actual gas production was used to back calculate the best-matched matrix permeability,which is 0.65μD for this particular work.Moreover,based on the breakout shape and induced volumetric strains around the borehole,drilling along the maximum horizontal stress does not necessarily lead to the best stability of the borehole,as generally believed.A drilling azimuth between 0and 60results in similar breakout width,whereas a drilling azimuth between 60and 90achieves the most efficient gas production.By considering both gas production efficiency and borehole stability,for this particular reservoir condition,the optimum drilling azimuth is determined to be between 45and 60.This study presents a practical approach for determining the optimum drilling azimuth in coal seam gas extraction through in seam boreholes.

Studying the direction of hydraulic fracture in carbonate reservoirs:Using machine learning to determine reservoir pressure

Hydraulic fracturing(HF)is an effective way to intensify oil production,which is currently widely used in various conditions,including complex carbonate reservoirs.In the conditions of the field under consideration,the hydraulic fracturing leads to a significant differentiation of technological efficiency indicators,which makes it expedient to study the patterns of crack formation in detail.Studies were carried out for all wells,which were considered as the objects of impact,to assess the spatial orientation of the cracks formed.The developed indirect method was used for this purpose,the reliability of which was confirmed by geophysical methods.During the analysis,it was found that in all cases,the crack is oriented in the direction of the section of the development system element characterized by the maximum reservoir pressure.At the same time,the reservoir pressure values for all wells were determined at one point in time(at the beginning of HF)using machine learning methods.The reliability of the machine learning methods used is confirmed by the high convergence with the actual(historical)reservoir pressures obtained during hydrodynamic studies of wells.The obtained conclusion about the influence of the reservoir pressure on the patterns of fracture formation should be taken into account when planning hydraulic fracturing under the conditions studied.