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

This study explores the geochemical reactions that can cause permeability loss in hydraulically fractured reservoirs. The experiments involved the reaction of powdered-rock samples with produced brines in batch reactor system at temperature of 95 °C and atmospheric pressure for 7-days and 30-days respectively. Results show changes in mineralogy and chemistry of rock and fluid samples respectively, therefore confirming chemical reactions between the two during the experiments. The mineralogical changes of the rock included decreases of pyrite and feldspar content, whilst carbonate and illite content showed an initial stability and increase respectively before decreasing. Results from analyses of post-reaction fluids generally corroborate the results obtained from mineralogical analyses. Integrating the results obtained from both rocks and fluids reveal a complex trend of reactions between rock and fluid samples which is summarized as follows. Dissolution of pyrite by oxygenated fluid causes transient and localized acidity which triggers the dissolution of feldspar, carbonates, and other minerals susceptible to dissolution under acidic conditions. The dissolution of minerals releases high concentrations of ions, some of which subsequently precipitate secondary minerals. On the field scale, the formation of secondary minerals in the pores and flow paths of hydrocarbons can cause significant reduction in the permeability of the reservoir, which will culminate in rapid productivity decline. This study provides an understanding of the geochemical rock–fluid reactions that impact long term permeability of shale reservoirs.

This study examines subsurface data from three wells to assess the shale gas potential of the Cretaceous-Paleocene succession of the Kohat Plateau, Pakistan. The petrophysical analysis was performed to calculate total organic carbon (TOC) using the Passey model. Petro-elastic parameters (Poisson ratio, Young modulus, and brittleness) and thermal maturity were also evaluated, respectively. The average TOC values in Makori-01 (as calculated by Passey's method) are 2.88 (wt%) for the Lockhart Limestone and 2.10 (wt%) for the Chichali-1 Formation. In Manzalai-02 well, the Lockhart, Hangu, Kawagarh, Lumshiwal, and Chichali formations TOC values are 2.81 (wt%), 2.55 (wt%), 2.32(wt%), 2.29 (wt%) and 2.20 (wt%) respectively. To exploit the unconventional resources, zones I and II in the Sumari Deep X-01 well (Chichali Formation) with an average TOC value of 2.71 (wt%) can be considered favorable areas for further evaluation. The volume of shale value is resulted as maximum within Chichali Formation in Makori-01 (58.52–75.89%), Manzalai-02 (54.09%), and Sumari Deep X-01 (70.47%), while the least value is noted within Lockhart Limestone in Makori-01 (12.25%) and Manzalai-02 (14.02%), and in Hangu Formation in Sumari Deep X-01 (12.39%). Also, the elastic properties reveal two to four zones of Young modulus, brittleness index, and Poisson’s ratio within the Chichali Formation in the studied three wells. The isopach maps show that the Patala, Lockhart, Hangu, Lumshiwal, and Chichali formations in the research area exhibit variable thicknesses. The 1D maturity models of the Makori-01 and Manzalai-02 wells indicate burial to a depth of 8 km approximately 2.5 Ma ago and the apex of oil production (1.1% Ro). The 1D maturity models indicate that the Sumari Deep X-01 well has encountered minimal burial (in terms of both time and depth) and, as a result, exhibits minimal potential source rock intervals. The volumetric estimate of unconventional recoverable gas resources is approximately 1.57 TCF in the study area. The integrated research provides the basis for tracking and assessing the unconventional resource potential, distribution, and characteristics within the studied basin.

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.

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.

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.

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.