Yao Lujian

Bio: Yao Lujian is an academic researcher from Northeastern University (China). The author has contributed to research in topics: Rock mass classification & Hydraulic fracturing. The author has an hindex of 3, co-authored 11 publications receiving 27 citations.

Numerical calculation and multi-factor analysis of slurry diffusion in an inclined geological fracture

Abstract: Slurry grouting plays an important role in water plugging for hydrogeological engineering and there are multiple factors that restrict the slurry flow. This study investigates the restriction mechanisms, based on a single inclined rough fracture, employing a space stepwise method (SSM) using multi-direction sectors (MDS) for calculating the diffusion of variable-viscosity slurry under constant flow. The specifically developed numerical algorithm is validated by experimental results. The spatio-temporal effects of major factors on the flow, and the rock hydraulic properties, were analyzed for cement-based slurry. The results show that the slurry flow calculated by MDS-SSM exhibits strong fitting with experimental results. The diffusion pattern no longer exhibits a circular plane, but rather a double semi-elliptical distribution. The fracture direction angle, especially for the upward vertical flow, must be considered in the case of a larger dip angle. The main controlling factor of the pressure field is the higher slurry viscosity in regions far from the injection hole, and the influence of dip angle is significantly greater closer to the hole. Roughness has an influence on the fracture hydraulic properties, and the required grouting pressure increases with an increase in roughness. The fracture aperture, viscosity coefficient, and diffusion radius are three key factors with strong sensitivity affecting the forecasting accuracy of grouting parameters. The role of the fracture dip angle can be neglected only in narrow fractures and long-distance diffusion with higher-viscosity slurry or larger pressure. The key threshold value can be obtained with a fitting formula under given conditions.

Penetrated crack rock mass grouting slurry diffusion test method

Abstract: The invention discloses a penetrated crack rock mass grouting slurry diffusion test method According to the method, based on site observation parameters, by means of the 3D printing technology, a hollow rock mass crack skeleton is constructed, monitoring elements are laid on the surface layer, the end portions and the joints of each crack, and the outer surface layer thickness of the skeleton meets similar rock mass strength attribute requirements; the hollow crack skeleton is connected with spotting capillary tubes, and thus the water saturation in the cracks is controlled; based on the skeleton, rock mass gravel similar to the rock mass gravel in a site is laid and subjected to cooling treatment, prestress corresponding to ground stress is applied on the two sides for compaction, drilling is conducted in proportion for going deep and then penetrating the cracks through perforation, and by means of a grouting pump, high temperature grouting is conducted on the interiors of the cracks; by means of a PC terminal and a thermal inductance instrument, the grouting process is observed, after grouting is completed, a device is detached, and the diffusion form of grouting in the cracks is observed The method is simple to operate, real-time diffusion of the grouting in penetrated crack rock mass and stress distribution during grouting are easily and truly reflected, and thus the method is an efficient test method for studying a complex crack rock mass grouting technology

Grouting experiment system for prefabricating cracked rock mass under excavation stress and using method

Abstract: The invention discloses a grouting experiment system for prefabricating a cracked rock mass under excavation stress and a using method. The system is based on a hydraulic fracturing technology, a mining stress field generated in excavation in an actual stope is considered, a complete large rock mass test sample manufactured by a rock mass is prefabricated into the cracked rock mass under the excavation stress, and then a grouting experiment is performed. Hydraulic fracturing is implemented at the top end part, and graded servo control loaders are arranged on the left side and the right side and at the bottom of a rock, so that the purpose of applying different loads on the rock mass in different directions is achieved, the direction of the maximal main stress born by a rock sample is changed by using the relation between hydraulic pressure and lateral load stress, and cracks are generated randomly in the rock mass. Besides, a grouting hole is drilled along a fracturing drill hole, theexperiment is completed by grouting the cracked rock mass, and an experiment basis is provided for analyzing the slurry diffusion rule and slurry-rock mass stability. The grouting experiment system issimple in structure, the experiment design is reasonable, the use is convenient, the cracked rock mass is efficiently and feasibly produced, and the grouting experiment is convenient and easy to implement.

Sound emission probe precise positioning device of rock uniaxial test and use method

Abstract: The invention discloses a sound emission probe precise positioning device of a rock uniaxial test and a use method. The device comprises an annular dial plate with a positioning hole and an annular nonius track, a nonius with a threaded hole and a set screw, a probe containing cap with a screw rod, and a scale bar; the nonius determines an orientation according to the annular dial plate; the annular dial plate is connected with the positioning hole by the scale bar; the scale bar has the effects of connecting and determining the position of the dial plate; one end, pointing to the inner side of the annular dial plate, of the screw rod is connected with the probe containing cap, and a sound emission probe is fixed by a spring (screw); during mounting, the screw rod is adjusted to increase frictional force between the probe and a rock test piece, and the probe and the positioning device are mounted on the surface of the rock test piece by using the frictional force. The device is flexible and convenient, and can perform sound emission probe precise positioning and fixing on rock test pieces with different shapes and sizes, meanwhile, the number and mounting orientation of the probe can be selected, and the time and vigor of researchers are effectively saved.

A method for evaluating formation conditions of complex fracturing fractures in tight reservoirs

Abstract: The invention discloses a method for evaluating formation conditions of complex fracturing fractures in tight reservoirs. This method takes the calculated fracture complexity index as a threshold value, and evaluates the effects of geo-stress difference, elastic parameters of target bed and interlayer, target bed thickness, porosity and permeability characteristics of target bed, operation displacement and fracturing fluid properties on the formation conditions of complex fracturing fractures. The method can clearly and intuitively give the three-dimensional spatial morphology of the whole process of the complex fracturing fracture from initiation to extension, the key influencing factors of fracturing complexity are analyzed one by one, good repeatability and high evaluation efficiency are exhibited, accurate identification of natural geomechanical conditions and artificial operation conditions in fracturing process are realized, and the method can effectively guide in-situ fracturingdesign, especially suitable for evaluation of complex fracture formation conditions in fracturing reconstruction of tight reservoirs with poor physical properties, low permeability and low natural productivity.

Multi-fracture interactions during two-phase flow of oil and water in deformable tight sandstone oil reservoirs

Abstract: Tight oil reservoirs are complex geological materials composed of solid matrix, pore structure, and mixed multiple phases of fluids, particularly for oil reservoirs suffering from high content of in situ pressurized water found in China. In this regard, a coupled model considering two-phase flow of oil and water, as well as deformation and damage evolution of porous media, is proposed and validated using associated results, including the oil depletion process, analytical solution of stress shadow effect, and physical experiments on multi-fracture interactions and fracture propagation in unsaturated seepage fields. Then, the proposed model is used to study the behavior of multi-fracture interactions in an unsaturated reservoir in presence of water and oil. The results show that conspicuous interactions exist among multiple induced fractures. Interaction behavior varies from extracted geological profiles of the reservoir due to in situ stress anisotropy. The differential pressures of water and that of oil in different regions of reservoir affect interactions and trajectories of multi-fractures to a considerable degree. The absolute value of reservoir average pressure is a dominant factor affecting fracture interactions and in favor of enhancing fracture network complexity. In addition, difference of reservoir average pressures in different regions of reservoir would promote the fracturing effectiveness. Factors affecting fracture interactions and reservoir treatment effectiveness are quantitatively estimated through stimulated reservoir area. This study confirms the significance of incorporating the two-phase flow process in analyses of multi-fracture interactions and fracture trajectory predictions during tight sandstone oil reservoir developments.

Study on Reasonable Roadway Position of Working Face under Strip Coal Pillar in Rock Burst Mine

Abstract: It is of great significance to study the reasonable position of mining roadway under strip coal pillar for increasing the stability of mining roadway, reducing the waste of resources, and realizing the safety production of working face. Based on the research background of the working face under the strip coal pillar in Jinqiao Coal Mine of Jining, Shandong Province, through theoretical analysis, similar material simulation experiment, and numerical simulation experiment, the stress distribution law, plastic failure range, and rationality of coal pillar setting in different width sections are systematically studied. Finally, the tailentry of working face is determined at the position of 5 m from the bottom of strip coal pillar to 1308 goaf. During the mining period of 1310 working face, the peak value of side abutment pressure is at the position of 3∼4 m; beyond 25 m in front of the coal wall, the deformation of the surrounding rock on the tailentry surface is small. After entering the advanced support section, the deformation of the two sides is mainly longitudinal crack expansion and local shallow small flakes; however, the roof is complete and stable. Therefore, the selection of tailentry location and coal pillar width has played a good role. The research results of this study can provide some reference for similar mine with similar geological and production technical conditions.

Grouting Mechanism in Water-Bearing Fractured Rock Based on Two-Phase Flow

Abstract: Grouting is always used in mine water plugging, reinforcement, and other disaster prevention projects. The diffusion mechanism of slurry in fractured rock is affected by geological environment and slurry performance, which should be revealed and characterized better. Based on the two-phase flow diffusion theory, a slurry diffusion model considering flowing water condition was established for a blocking area of a fracture zone in one case from China. The feasibility of two-phase flow model in grouting diffusion calculation was analyzed. The diffusion model in dynamic water environment was studied, and the diffusion range varying with time in the grouting area of Zhangji Coal Mine was explored. The optimization method of multi grouting holes was put forward, and the influence of water flowing was discussed. The results show that the slurry diffusion calculated by the two-phase flow model was feasible and consistent with the experimental study. The dynamic water can change the conventional circular diffusion state of slurry, but its pattern was oval and leaf type. There were different penetration distances in directions, and typical grouting voids were made on the side and upstream. When the single-hole grouting was carried out, the predetermined value can be achieved in the height range, but it was only about 15 m on the side because of the water flowing, which cannot meet the requirements. The optimization scheme of grouting was put forward, which adopted multiple grouting holes in the long side, and grouting in different directions and periods to avoid the possible problems of multihole intersection. The rationality and effectiveness of the proposed optimization method were verified through the calculation of water yield and analysis of cement composition from the drilling core in the grouted zone. In the grouting process, the water flowing has double effects, which has a significant role in promoting and scouring along the flow direction, but there is a significant weakness in the side diffusion. It is very important to realize the rational use of the dynamic water through the optimization scheme. This study is an important basic work of grouting mechanism, and it is expected to promote the development of grouting technology and application of two-phase fluid-solid coupling theory.