Development of an ultra-high-pressure rotary combined dynamic seal and experimental study on its sealing performance in deep energy mining conditions

With the continuous development of deep oil and gas,minerals,geothermal resources,and other resources,there are increasingly more stringent requirements for equipment.In particular,the ultra-highpressure dynamic seals of deep mining device need to be developed.Therefore,considering the use of dynamic seals in unique deep mining environments,an ultra-high-pressure rotating combined dynamic seal was designed and developed and its sealing performance was experimentally measured and analyzed.The results show that the experimental device can operate stably under a pressure of up to150 MPa and a rotating speed of 76 r/min,and can also operate normally under a rotating speed of up to 140 r/min and a sealing pressure of 120 MPa.During the operation of the ultra-high-pressure rotating combined dynamic seal,the sealing ring does not show obvious damage,which vouches for its sealing performance.No leakage of flow and pressure was detected in the all seal structures within the sealing pressure range of 0-150 MPa.Therefore,the dynamic sealing performance of the device is intact under ultra-high-pressure conditions and can be applied in deep mining environments at a certain depth.The research and development of this device can aid future deep energy exploration and exploitation.

Thermal effects on prediction accuracy of dense granite mechanical behaviors using modified maximum tangential stress criterion

Thermally-induced changes in the fracture properties of geological reservoir rocks can influence their stability,transport characteristics,and performance related to various deep subsurface energy projects.The modified maximum tangential stress(MMTS)criterion is a classical theory for predicting the fracture instability of rocks.However,there is a lack of research on the accuracy of MMTS theory when rocks are subjected to different temperatures.In this study,mechanical theoretical analysis and failure and fracture mechanics experiments of granite under the influence of temperatures ranging from 20℃to 600℃are carried out.The results showed that the theoretical estimated value of MMTS differs significantly from the experimental data at 20℃-600℃.The Keff/KIC ratio is less than the experimental test value due to the critical crack growth radius(rc)estimated by the conventional method being larger than the critical crack growth radius(rce)derived from the experimental data.Varied temperatures affect the fracture process zone size of fine-grained,compact granite,and the MMTS theoretical estimation results.Therefore,it is essential to modify the critical crack growth radius for MMTS theory to accurately predict the fracture characteristics of thermally damaged rocks.In addition,the variation of the rock’s me-chanical properties with temperature and its causes are obtained.Between 20℃and 600℃,the mode-Ⅰ,mode-Ⅱ,and mixed-mode(a-30℃and 45℃)fracture toughness and Brazilian splitting strength of the granite decrease by 80%and 73%,respectively.When the rock is heated above 400℃,its deterioration is mainly caused by a widening of its original cracks.

Real-time pore structure evolution difference between deep and shallow coal during gas adsorption:A study based on synchrotron radiation small-angle X-ray scattering

Coal seam CO_(2) sequestration is an important option to address global warming.A better knowledge on coal pore structure evolution during gas adsorption can provide guidance for coal seams CO_(2) seques-tration.However,few investigations on the pore structure evolution differences between the deep and shallow coal were conducted during gas adsorption.In this study,based on the real-time synchrotron radiation small-angle X-ray scattering(SAXS)observation,the average pore diameter and pore surface fractal dimension evolution differences between deep and shallow coal were investigated from the as-pects of coal compositions and stress history.Two types of coal deformation(inner-swelling and outer-swelling)coexist during gas adsorption.Coal compositions have significant impact on the dominance of deformation type.The dominance of inner-swelling in deep coal is induced by the higher ash contents,and there is the decrease of average pore diameter during gas adsorption.The impact of stress-history(burial depth)on adsorption-induced deformation is more prominent than that of gas adsorption ca-pacity.In deep coal,the surface fractal dimension evolution presents a negative correlation with the evolution of pore diameters.In shallow coal,the surface fractal dimension evolution presents a Langmuir-type correlation with the adsorption time.

冲击荷载下同时测量纯Ⅰ型和Ⅱ型裂纹的起裂韧度

为了在一个试件中同时测量纯Ⅰ型和Ⅱ型裂纹的动态起裂韧度,设计了一种大尺寸双裂纹凹凸板试件,利用落锤板冲击装置开展不同加载率的落锤冲击实验。采用高精度应变片测量冲击载荷和裂纹萌生时间。采用动态有限差分程序AUTODYN建立相应的数值模型,利用试验-数值方法确定裂纹的动态起裂韧度。实验和数值研究表明,双裂纹凹凸板试样适合用于同时测量纯Ⅰ型和Ⅱ型裂纹的动态起裂韧度;动态起裂韧度随着加载率的增加而增加,裂纹萌生时间随着加载率的增加而减小;在相同加载率下,纯Ⅱ型裂纹的起裂韧度大约是纯Ⅰ型裂纹的0.5倍;随着试样底部预制裂缝长度从20 mm增加到100 mm,纯Ⅰ型裂纹的动态起裂韧度逐渐降低,表明底部预制裂纹长度越长Ⅰ型裂纹越容易起裂,但纯Ⅱ型裂纹的动态起裂韧度变化不大。

Doping level effects in Gd/Cr co-doped Bi_(3)TiNbO_(9) Aurivillius-type ceramics with improved electrical properties

In this work, different amount of Cr_(2)O_(3) (x - 0e0.3 wt%) as dopant were doped into the Aurivillius-typecompound Bi2.8Gd0.2TiNbO9 (BGTN), such a kind of Gd/Cr co-doped Bi3TiNbO9 ceramics with improvedelectrical properties were synthesized by the convenient solid-state reaction route. The substitution of Cr^(3+) for Ti^(4+) at B-site induced the lattice distortion of pseduo-perovskite layer. Fewer Cr_(2)O_(3) dopant(x<0.2) resulted in the grain refinement of ceramics. After Cr_(2)O_(3) was added into BGTN, TC decreased tothe vicinity of 908 ℃. Below TC, the relaxed dielectric response resulted from charge carriers hoppinginduced another board dielectric permittivity peak, whose starting temperature shifts toward lower sidegradually with increase of x. The values of Eacon calculated from the Arrhenius relationship betweenconductivity and temperature indicated the intrinsic conduction at high temperature is dominated by thelong-range migration of doubly ionized oxygen vacancies. Moderate Cr_(2)O_(3) dopant (x=0.1e0.25) areconducive to the enhancement of piezoelectric property and thermal stability. The sample with x=0.2 achieved both a high T_(C)~903 - C and a high d_(33)~18 pC/N at the same time. Also, its d33 can retain 80% ofthe initial value after the sample was annealed at 800 - C for 4 h.