Geomechanics and Geophysics for Geo-Energy and Geo-Resources最新文献

Mine water inflow is an important basis for the formulation of mining plans and the utilization of groundwater resources. The mine water inflow is the result of the combined influence of many factors. The weight value of the influencing factors is calculated by the entropy method, and the order of importance of the factors is: precipitation > mining depth > cumulative mined-out area > aquifer thickness > mining area > mining height. The optimal univariate nonlinear regression model of mine water inflow to each influencing factor is obtained by factor scatter analysis and Matlab function programming. On this basis, combined with the weight values of factors, a multivariate nonlinear regression prediction model of mine water inflow based on weighting is innovatively established, which overcomes the defect that the traditional water inflow prediction method that cannot reflect the relative importance differences of various influencing factors. The multivariate weighted nonlinear regression model is used to predict the mine water inflow of typical coal mines, and the prediction results are compared with the linear regression model and the measured value. The results show that the prediction model of mine water inflow based on weighted multivariate nonlinear regression is accurate higher, with higher practical application value.

To enhance the drilling efficiency and extend the service life of PDC (Polycrystalline Diamond Composite) bits in shale formations, this study delves into the rock-breaking mechanisms of special-shaped cutters through a comprehensive experimental approach. This involves optimizing the cutter designs, conducting laboratory experiment and field testing. Among the various cutter geometries considered, concave, axe, planar, and triangular cutters are chosen as the focal points for unit rock-breaking experiments. These tests aim to assess their cutting loads and cutting specific energy to gain a deeper understanding of their performance characteristics. Based on experimental, the debris characteristics are analyzed. Based on the understanding of the shale-breaking characteristics of special-shaped cutters, field testing is performed using a novel PDC bit with a special-shaped cutter. Compared with planar cutters, the concave cutter and the triangular cutter generate lower cutting loads and cutting specific energy. Under identical conditions, the average cutting force and cutting specific energy of concave cutter at different cutting depths are reduced by 16.1% and 19.6% Specifically, the concave cutter generates the largest debris when operated under similar conditions, which is beneficial for increasing rock-breaking efficiency. Laboratory experiment indicate that compared to conventional drill bits, the novel drill bit experiences an increase in torque of approximately 9.8% with increasing WOB (weight on bit). Under high WOB, the ROP (rate of penetration) increases by about 75.4%, while the mechanical specific energy decreases by nearly 40%. Additionally, the novel bit vibration characteristics remain superior to conventional drill bits. Field testing shows that the average ROP of the novel bit and total footage drilled increase by up to 13.3% and 27.2%, respectively, in comparison with those for the conventional bit. The research results are helpful to speed up the efficiency of shale gas drilling.

Having an accurate understanding of the scale effect of surface morphology characteristics is crucial to examining the mechanical behavior of rock structural plane. At present, the quantification and sampling methods of surface morphology show diversity, which is the potential reason for the inconsistent research conclusions on scale effect. Firstly, based on mathematical statistics and correlation analysis, the most representative parameter is proposed from hundreds of morphological parameters. Then, the previous scale effect sampling methods are analyzed. In order to ensure that the selected samples are representative, a novel sampling method, considering all morphological information, is proposed. By means of the novel quantification and sampling methods, the size effect characteristics are systematically analyzed. Under the conditions of different rock types, shear directions and sampling locations, etc., discontinuity roughness does not change significantly with sampling scale. As sampling scale increases, the distribution range of representative samples is gradually concentrated, the total amount decreases, and the proportion increases. However, the distribution of representative samples on the initial structural plane does not show obvious regularity. These findings would provide theoretical support for the deformation control and stability analysis of rock mass in engineering.

The macro and micro morphology of rock failure surfaces play crucial roles in determining the rock mechanical and seepage properties. The morphology of unloaded deep rock failure surfaces exhibits significant variability and complexity. Surface roughness is closely linked to both shear strength and crack seepage behavior. Understanding these morphology parameters is vital for comprehending the mechanical behavior and seepage characteristics of rock masses. In this study, three-dimensional optical scanning technology was employed to analyze the micromorphological properties of limestone and sandstone failure surfaces under varying stress conditions. Line and surface roughness characteristics of different rock failure surfaces were then determined. Our findings reveal a critical confining pressure value (12 MPa) that influences the damage features of Ordovician limestone failure surfaces. With increasing confining pressure, pore depth and crack formation connecting the pores also increase. Beyond the critical confining pressure, the mesoscopic roughness of the failure surface decreases, and the range of interval-distributed pore roughness diminishes. Additionally, we conducted a detailed investigation into the water conductivity properties of rocks under different stress states using Barton's joint roughness coefficient (JRC) index and rock fractal theory. The roughness features of rock failure surfaces were classified into three categories based on mesoscopic pore and crack undulation forms: straight, wavy, and jagged. We also observed significant confining pressure effects on limestone and sandstone, which exceeding the critical confining pressure led to increased water conductivity in both rocks, albeit through different mechanisms. While sandstone exhibits fissures running across it, limestone shows shear abrasion holes. Beyond the critical confining pressure, the rock failure surface becomes smoother, leading to decreased water flow blocking capacity. The fractal dimension of Ordovician limestone increases significantly under critical confining pressure, leading to a more complex mesoscopic crack extension route.

Fluid movability in tight sands may not be accurately characterized by pore size-based classification methods solely because of the complex pore structure and heterogeneity in pore size. In this study, on the basis of casting thin slices and scanning electron microscope observation, pore structure was analyzed using mercury injection, NMR, and micron CT to classify and evaluate the tight oil reservoir. The experiment suggest that the quality of tight reservoir is determined by its pore structure, particularly the throat radius, with the microthroat being an essential factor in permeability. Uniquely, we divide the reservoir by Q-cluster with throat radius, displacement pressure, permeability and other parameters. Based on reservoir classification, this study proposed a method for studying the pore size classification of samples on the T₂ spectrum by combining CT scanning with mercury intrusion and a NMR experiment. Pore fluids are generally classified into movable fluid and irreducible fluid by one or two NMR T₂ cut-offs. The pore size distributions and capillarity boundaries are converted from T₂ and mercury injection capillary pressure (MICP). We categorized pores into micropores (T₂ < 1), macropores (T₂ > 10, with T₂ > 300 as fractures), and medium pores (the rest). The saturation of movable fluid and the percentage of micro-fractures can characterize the seepage characteristics of tight reservoirs, which is of great significance for the later periods of oilfield development.

In this study, a comprehensive parameter determination procedure for the Johnson–Holmquist–Cook (JHC) constitutive model is introduced, including calibration and validation processes for Indiana Limestone rocks. The procedure is conducted utilizing the existing physical and mechanical properties of Indiana Limestone. To obtain an accurate set of parameters for the JHC model for Indiana Limestone, an extensive dataset comprising mechanical and physical properties of Indiana Limestone rocks was initially compiled. The static mechanical tests incorporated uniaxial compression, triaxial compression, direct tensile, and uniaxial strain data, while the dynamic mechanical test data was primarily derived from the Split Hopkinson Pressure Bar experiments. Subsequently, the JHC constitutive model parameters were determined using existing literature data, employing statistical analysis, theoretical derivation, and numerical back analysis techniques. One of the damage parameters was determined through numerical post-peak behavior calibration of triaxial compression strength test results on experimental data. Finally, the accuracy of the determined parameters was validated by comparing the numerical and experimental results of both static and dynamic tests. This study effectively addresses the challenges associated with the numerical method using the JHC material model, such as the complex parameter determination process and the costly required tests, thereby preserving the efficiency and applicability of the numerical method.

To see if and how abrasive potential as well as drilling efficiency change due to rock heating, Cerchar scratch tests were performed on six types of rock at eight temperature levels. Results indicate that rock abrasivity is temperature-dependent. The change of rock abrasivity expressed by the Cerchar abrasivity index can be divided into two stages on either side of 500 °C. Meanwhile, the drilling efficiency expressed by the Cerchar abrasion ratio can significantly be enhanced, especially when the heating temperature exceeds 500 °C. The observation of damaged surfaces indicates that the material volume removed from the rock surface increase after rock heating. The worn steel surfaces (115CrV3 tool steel) shows the severe plastic deformation and fracturing associated with cracking, delamination, dislocation and chipping of the steel.

Advanced identification of the potential sliding surface of a slope and accurate early warning are crucial prerequisites for effective management of landslides and timely and prevention of catastrophic accidents. This study analyzes the statistical characteristics of landslide displacement evolution. Based on the normal distribution theory, random variables of displacement velocity and acceleration with random errors are introduced into the analysis of surface displacement information, and random variables of relative displacement with random errors are introduced into the analysis of deep displacement information. When the random variables do not follow the normal distribution, the warning time can be obtained. Therefore, an advanced landslide classification warning method is established. The analysis results showed that analysis results from the April 30 landslide project at an open pit mine indicate that the earliest warning time for landslide initiation is 2020/2/19, while the earliest warnings for acceleration occur on 2020/4/15 and the fast acceleration on 2020/4/25. These three-level warning times align with reality, and the inferred slip surface position corresponds to the actual weak layer range. The primary power source driving landslide originates from behind the sliding body which subsequently pushes rock mass along weak layers near the south wing, north wing, and front in succession. Research findings can enhance landslide warning accuracy, facilitate advance identification of sliding surface, provide scientific basis for open-pit slope engineering design, as well as mitigate casualties and property losses.

As the main reservoir of coalbed gas in southeastern Sichuan, the mudstone of the Permian Longtan Formation has been drilled to obtain industrial gas, but the level of exploration and development is low. The researches on the types of lithological assemblages, reservoir characteristics, and gas-bearing properties are poor, which limits the evaluation and selection of the sweet point area for the marine-continental transitional shale gas. In this paper, by comparing the differential of different lithological distribution in the well L3, multiple discriminant functions and logging interpretation models for different lithology are established to determine the classification criteria of lithological assemblage types of shale formations. Based on the experimental results of high-temperature and high-pressure isothermal adsorption, the reservoir space distribution and gas-bearing characteristics of mudstone in different lithological assemblages are compared and analyzed. It is indicated that the four lithological assemblage types are found in the Permian Longtan Formation, including thick mudstone with the interlayer of coalbed (Type I), rich mudstone with the interlayer of sandstone and thin coalbed (Type II), sandstone interbedded with mudstone with the interlayer of coalbed (Type III), and limestone interbedded with sandstone with the interlayer of mudstone (Type IV), which are superimposed with each other. The different pore structure characteristics of mudstone in different lithological assemblages is the main influencing factor of differential gas-bearing property. The dominant lithological assemblages are Type I and Type II. Coalbed and carbonaceous mudstone are the source rock and primary storage space of adsorbed gas. Moreover, with low porosity and permeability, high breakthrough pressure and the strong sealing capacity of regional mudstone, it is easy to form the “microtrap” to store the natural gas. The sealing capacity of mudstone provides a favorable condition for gas preserve. Under the dynamic condition of hydrocarbon generation, the pressure storage box is formed, accompanied with the fine reservoir spaces and gas-bearing contents.

The shear and tensile stabilities of highly inclined non-circular wellbores are investigated in this study. Using the equivalent-ellipse hypothesis, the non-circular geometry was approximated as an ellipse, and the corresponding stress concentration equations are presented. With the new set of stress concentration equations, a comprehensive study of the tensile and shear stabilities of an elliptical borehole was conducted, including the impact of well inclination and azimuthal angles, horizontal stress difference, degree of ellipticity, and orientation of the maximum horizontal stress to the major axis of the ellipse. Using five commonly used shear failure criteria, we observed that both Mohr–Coulomb and Drucker Prager (inscribed) failure criteria predicted higher collapse pressures, relative to the others including Drucker Prager (inscribed), Mogi-Coulomb, and Modified Lade. While Drucker Prager's (circumscribed) failure criterion underestimates the collapse pressure. Both the linear elastic and poroelastic models were used in investigating the fracture initiation orientation and pressure of highly inclined elliptical boreholes. The prediction from the poroelastic model is always less than the linear elastic model. In some instances, they predict different fracture initiation orientations. From this study, we observed that generally, a near-circular wellbore is more stable than elliptical borehole in both shear and tension. Nevertheless, there are some well inclination and azimuthal angles than can make an elliptical borehole have more shear and tensile stabilities than a near-circular wellbore.