The enhanced geothermal system (EGS) reservoir consists of a heterogeneous fracture network and rock matrix, and the heterogeneity of the reservoir has a significant influence on the system’s electricity generation performance. In this study, we numerically investigated the influence of reservoir heterogeneity on system production performance based on geological data from the Gonghe Basin geothermal field, and analyzed the main factors affecting production performance. The results show that with the increase of reservoir heterogeneity, the water conduction ability of the reservoir gradually reduces, the water production rate slowly decreases, and this causes the electric power to gradually reduce, the reservoir impedance to gradually increase, the pump power to gradually decrease and the energy efficiency to gradually increase. The fracture spacing, well spacing and injection temperature all have a significant influence on electricity generation performance. Increasing the fracture spacing will significantly reduce electric power, while having only a very slight effect on reservoir impedance and pump power, thus significantly decreasing energy efficiency. Increasing the well spacing will significantly increase the electric power, while having only a very slight effect on the reservoir impedance and pump power, thus significantly increasing energy efficiency. Increasing the injection temperature will obviously reduce the electric power, decrease the reservoir impedance and pump power, and thus reduce energy efficiency.

According to the problems of long time self consolidation and the drain pipes are easy to block of high viscous dredger fill in the actual engineering projects, this paper firstly puts forward the idea of self-weight consolidation method which hydraulic filling and drainage consolidate at the same time and the method of hierarchical vacuum preloading which applies vacuum pressure step-by-step, and carries out laboratory test, at the meanwhile, takes physical and chemical tests and mercury intrusion porosimetry of dredger fill after each consolidation stage. The test results show that: the two curves of settlement and pore water pressure all show downward trend, in the late hierarchical vacuum preloading stage, the two curves all tend to horizontal due to the accomplishment of consolidation of dredger fill; the moisture content and the soluble salt content decreases gradually, the strength increases gradually in the consolidation process of dredger fill. The physical and chemical properties of dredger fill have been improved after the hierarchical vacuum preloading, and doesn't appear the phenomenon of blocking drain pipe, the reinforce effect is uniformity; the total pore volume, porosity and the average pore diameter of dredger fill are all gradually reducing, and the larger pores are first compressed into smaller, and then the smaller pores are compressed; the pore distribution of dredger fill develops from large size pore to small size pore; The nearer to the drain pipe, the smaller settlement of dredger fill is, the faster pore water pressure dissipates, and the smaller porosity is; in contrary, the farther to the drain pipe, the greater settlement of dredger fill is, the slower pore water pressure dissipates, and the bigger porosity is.

The main conditions affecting electricity generation performance of an enhanced geothermal system (EGS) include reservoir porosity, reservoir permeability, rock heat conductivity, water production rate and injection temperature. Presently there is lack of systematic research the relative importance of the five aforementioned conditions. The orthogonal test method is a statistical approach to analyze multi-factor and multi-level influence on system performance. In this work, based on the geological data at Yangbajing geothermal field, we analyzed the five conditions affecting the electricity generation performance of EGS, and ranked the relative importance of the five factors. The results show that the order of the relative importance of the conditions on electric power is water production rate > injection temperature > reservoir porosity > rock heat conductivity > reservoir permeability; the order of the relative importance of the conditions on reservoir impedance is reservoir permeability > injection temperature > water production rate > reservoir porosity > rock heat conductivity; the order of the relative importance of the conditions on pump power is water production rate > reservoir permeability > injection temperature > reservoir porosity > rock heat conductivity, and; the order of the relative importance of the conditions on energy efficiency is water production rate > reservoir permeability > reservoir porosity > injection temperature > rock heat conductivity. The construction of an EGS reservoir should be located at a formation with higher reservoir porosity or rock heat conductivity, while the determination of reservoir permeability, water production rate and injection temperature should be based on the comprehensive target.

Due to the co-existence of multiple organics and multiple length scales of the structure, quantitative characterization of the microstructure of organic matter in hydraulic mud consolidations, and understanding the impact on its mechanical properties have been challenging topics. This article attempts to tackle the challenge using lab experiments and a data-constrained modelling (DCM) approach combined with multi-energy synchrotron-based X-ray micro-CT (computed tomography). In this paper, scanning electron microscopy (SEM) and other different technical means were combined to study the microstructure of hydraulic mud composition and distribution. One unmodified hydraulic mud and four remolded samples were analyzed in vacuum preloading tests corresponding to organic matter contents of 1.65%, 3.75%, 5.15%, 8.65%, and 11.15%, respectively. Organic matter plays a significant role in hindering the shear strength of consolidation. Macro- and microstructure under different pressures could be extracted by the DCM and X-ray CT. The DCM-reconstructed microstructure of fine-grained soil from hydraulic mud is presented by four groups: organic matter, two groups of minerals, and pores. Different groups are displayed with different colors, which could clarify the distributions and density degrees of each component (group). The macro- and microstructures and the distribution of organic matter were quantified and compared among groups. It was demonstrated that the mechanical properties of the organic matter were closely correlated to the meso- and nano-scale clusters of porosity and minerals. The variation of organic clusters with loading pressure, and the number of sub-macro organic clusters, were small. Three scales of organic cluster (40–400 μm, 4–40 μm, and 0.4–4 μm) changed visibly in consolidation at 200 kPa and 800 kPa. The analysis has shown that pressures of 100 kPa and 400 kPa could be used as two characteristic values of structure change of hydraulic mud, which perhaps matched the turning points of destruction. The DCM approach, combined with multi-energy synchrotron-based X-ray micro-CT presented here, are applicable in studying the relationship between the microstructure and macro-properties for various other engineering materials.

The results of the three-dimensional reconstruction of soil were derived from the X-ray absorption coefficient of the material itself. However, the absorption coefficient is not a fixed value, and is related to densities, chemical molecular weight, and the weight percentages of chemical components. How to accurately obtain the density of one component is a vital issue in multi-materials. In this study, the influence of the physical parameters of each component in the data-constrained modeling (DCM) of the microstructure of soft clay was investigated. The results showed that density changes were more prominent. A reasonable multi-component density was calculated, and the density of organic matter had a significant effect on the volume percentage of three-dimensional soft clay. In the clay mineral montmorillonite, the density significantly affected the volume percentage data, which directly limited the accuracy of the material distribution analysis. Based on this, other physical parameters of each component in the data constraint model could be further explored. Based on the density value of the simple material, a reasonable multi-materials density was calculated, which provides a quantitative method for the evolution analysis of soil structure.

Through the use of the particle flow software simulation, the influences on the microscopic dynamic properties of high viscosity soft soil caused by the inner diameter, cut angle and wall thickness of the samplers were studied with the example of the dredged mud. The motion behavior of the inflection point of particle characteristics was compared in seven soil samples by dividing the soil layers. The results show that a convective displacement field of the soil particles is formed at the bottom, and the particles above the convection are mainly subject to tensile expansion while the particles below the convection are mainly compressed and contracted, which result in the regular changes in porosity and bending deformation of the soil layers. There is a synergistic relationship between the intersection of the porosity curve and the initial porosity curve and the convective position of the particle displacement field. There is a characteristic inflection point in the interlayer particle displacement with the soil layers behave as a bending deformation. The particle disturbance between the inflection points is not obvious and the particle disturbance outside the inflection points is larger. The deformation feature can be fitted to a rotating paraboloid with the lower opening and the disturbance of the seven groups soil samples can be assessed initially by the a value of the surface equation. The line connecting the inflection points of the interlayer features can be refitted to a paraboloid of rotation. The ratio of the volume of the paraboloid to the volume of the soil sample can be used to evaluate the originality of the soil sample.