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Using salt caverns for an underground strategic petroleum reserve (SPR) is considered as an ideal approach due to the excellent characteristics of low porosity, low permeability, self-healing of damage, and strong plastic deformation ability of rock salt. Salt deposits in China are mostly layered rock salt structures, with the characteristics of many interlayers, bringing great challenges for the construction of SPR facilities. Studying the microscopic pore characteristics of the rock surrounding SPR salt caverns in different environments (with brine and crude oil erosion) is necessary because the essence of mechanical and permeability characteristics is the macroscopic embodiment of the microscopic pore structure. In this paper, XRD tests and SEM tests are carried out to determine the physical properties of storage media and surrounding rock. Gas adsorption tests and mercury intrusion tests are carried out to analyze the microscopic pore structure, specific surface area variation and total aperture distribution characteristics of SPR salt cavern host rock. Results show that: (1) Large numbers of cores in interlayer and caprock may provide favorable channels for the leakage of high-pressure crude oil and brine. (2) The blockage of pores by macromolecular organic matter (colloid and asphaltene) in crude oil will not significantly change the structural characteristics of the rock skeleton, which is beneficial to the long-term operation of the SPR salt cavern. (3) The water–rock interaction will bring obvious changes in the micro-pore structure of rock and increase the leakage risk of the storage medium. The results can provide theoretical bases and methods for the tightness analysis of China’s first underground SPR salt cavern.

The design of dam bodies for underground reservoirs must account for how water affects shear failure and the evolution of fractures in coal pillars. In this work, we detect acoustic emissions in raw coal samples with different water content (0%, 5.35%, 17.88%, and 20.40%) and under uniaxial compression shear and use computed tomography to analyze the failed samples. The results show that the shear strength, shear displacement, cohesion, and internal friction angle all decrease with increasing water content, which is described by the revised Mohr‐Coulomb model for the case of water intrusion. The acoustic emission counts correlate strongly with the change in stress, and the cumulative acoustic emission counts are combined with shear stiffness to separate the fracture evolution process into five stages: crack closure, elastic deformation, stable crack propagation, unstable crack propagation, and failure. The ratios of the crack closure, initiation, and damage stress to the corresponding peak shear stress are essentially unaffected by the water content. Most cracks are tensile cracks, and an increase in the water content promotes the development of parallel fractures. These results are helpful for determining the size of coal pillars in underground reservoirs and for solving other underground engineering problems, such as support for water‐rich coal roadways.

To fully utilize the abandoned salt cavern resources and to increase the total amount of the fossil energy reserve of China, reconstructing some of these salt caverns for underground gas storage (UGS) or strategic petroleum reserve (SPR) would be an effective method. The salt resources in China mainly are bedded salt, which brings great challenges for the cavern construction and safety evaluation. In this paper, the investigations are presented to evaluate the tightness of the UGS and SPR salt cavern facilities, located in the bedded rock of Jintan, China. Microcosmic analysis, and permeability and porosity tests of the surrounding rock are carried out to determine their properties, which provide the basic data for the tightness assessment. A 3-D numerical model is developed based on the test results and the geological features of the target formation. The numerical simulation results show that the seepage velocity, seepage range and loss rate of leakage of the SPR salt caverns are much smaller than those of UGS salt caverns. The cavern's pillar width with a pillar to diameter ratio (P/D) of 1.5 can satisfy the tightness requirement of SPR salt caverns, but it cannot meet the requirement of UGS caverns. This indicates that some existing abandoned salt caverns in Jintan which are unsuitable for UGS due to their small pillar width have the potential to be rebuilt for SPR. This would help to increase the storage capacity of crude oil in China. The results can also provide a reference for the implementation of similar projects in other bedded salt districts. INDEX TERMS Bedded rock salt, underground gas storage, strategic petroleum reserve, tightness, seepage.

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As an important part of face recognition, facial image segmentation has become a focus of human feature detection. In this paper, the AdaBoost algorithm and the Gabor texture analysis algorithm are used to segment an image containing multiple faces, which effectively reduces the false detection rate of facial image segmentation. In facial image segmentation, the image containing face information is first analyzed for texture using the Gabor algorithm, and appropriate thresholds are set with different thresholds of skin-like areas, where skin-like areas in the image’s background information are removed. Then, the AdaBoost algorithm is used to detect face regions, and finally, the detected face regions are segmented. Experiments show that this method can quickly and accurately segment faces in an image and effectively reduce the rate of missed and false detections.

During upward backfill mining of the close-distance coal seam group, the reasonable design of the backfill body compaction ratio (BBCR) of lower coal seam goaf plays a key role in controlling overburden strata movement and deformation. In this paper, the feasibility discrimination method of upward caving mining was adopted; it was found that when the coal seam spacing was small, the recovery was not possible due to the instability of the upper coal strata equilibrium structure caused by the mining. Hence, the upward backfill mining method was proposed; combined with the migration control mechanism of backfill mining overburden strata, the dynamic evolution of crack propagation height of overburden strata during upward backfill mining was analyzed. Based on that, a layer spacing-BBCR-mining height (L-R-H) prediction model based on multiple linear regression analysis was established and the BBCR of close-distance coal seam group safe upward mining was determined combined with the engineering background. The results demonstrate that the main controlling factors of crack propagation in overburden strata during upward backfill mining were BBCR and mining height; the crack propagation height in overburden strata caused by mining decreased exponentially with the increase of BBCR and increased with the increase of mining height linearly. The lower coal seam engineering safety BBCR of upward backfill mining in the Dafosi Coal Mine was 87.2%, and the close-distance coal seam group safe upward mining was realized.

Short-wall block backfill mining (SBBM) technology is an effective method to solve the environmental problems in the mining process. Based on the technical characteristics of SBBM technology and the physical similarity criterion, the physical similarity models for comparing the control effects of water-flowing fracture (WFF) development using short-wall block cave mining (SBCM) and SBBM were established, and the deformation and the WFF development of overlying strata above gob were monitored. The test results determined that the composite materials of 5 mm thick pearl sponge+5 mm thick sponge+10 mm thick paper+6 mm thick board were adopted as the similar backfill materials by comparing the stress-strain curves between the similar backfill materials and the original gangue sample. When the backfilling body was filled into the gob, it would be the permanent bearing body, which bore the load of the overlying strata accompanied with the protective coal pillar. At the same time, the backfilling body also filled the collapse space of overlying strata, which was equivalent to reduce the mining height, and effectively reduced the subsidence and failure height of the overlying strata. Compared with SBCM, the test results showed that the maximum vertical deformation, the height of water-flowing fractured zone, and activity range of overlying strata using SBBM were reduced by 91.4%, 82.5%, and 64.9%, respectively. SBBM had a significant control effect on strata damage and WFF development, which could realize the purpose of water resource protection in coal mines.