Permeability evolution and gas flow in wet coal under non-equilibrium state:Considering both water swelling and process-based gas swelling

Accurate knowledge of gas flow within the reservoir and related controlling factors will be important for enhancing the production of coal bed methane.At present,most studies focused on the permeability evolution of dry coal under gas adsorption equilibrium,gas flow and gas diffusion within wet coal under the generally non-equilibrium state are often ignored in the process of gas recovery.In this study,an improved apparent permeability model is proposed which accommodates the water and gas adsorption,stress dependence,water film thickness and gas flow regimes.In the process of modeling,the water adsorption is only affected by water content while the gas adsorption is time and water content dependent;based on poroelastic mechanics,the effective fracture aperture and effective pore radius are derived;and then the variation in water film thickness for different pore types under the effect of water content,stress and adsorption swelling are modeled;the flow regimes are considered based on Beskok’s model.Further,after validation with experimental data,the proposed model was applied to numerical simulations to investigate the evolution of permeability-related factors under the effect of different water contents.The gas flow in wet coal under the non-equilibrium state is explicitly revealed.

Modular growth and clonal propagation of Hippophae rhamnoides subsp, sinensis in response to irrigation intensity

A multipurpose clone plant species, Hippophae rhamniodes has the capacity for indefinite longevity, although under successive drought stress it may often decline or die across large areas. Field trials were con- ducted over 2 years to examine the effects of varied irrigation intensities on modular growth and clonal propagation in a semi-arid area. Irrigation levels included a control, as well as two, four and six times the volume of water that was typically received via local annual average precipitation. Irrigation intensity significantly influenced clonal propagation capacity （number of daughter ramets）, aboveground modular growth （height, base diameter, and crown width）, belowground modular growth included root nodule dry weight, stretching capacity of lateral roots （length of the longest lateral roots, and diameter of first-grade lateral roots）, and branching intensity of lateral roots （number of lateral roots bifurcation grade, number of first- grade lateral roots）. The modular growth and the density of daughter ramets were small under non-irrigation or low irrigation, and became larger with increased irrigation intensity. Beyond a certain threshold, however, further increases in irrigation intensity resulted in a reversion to the development. The optimal irrigation intensities for growth and propagation were 3.48-5.29 times the volume of nominal local annual average precipitation. There were effects of irrigation intensities on the positive significant correlations between aboveground and belowground modular growths, and on clonal propagation capacities. Under various water treatments, H. rhamnoides may adapt to the environment through the regulation of growth and propagation. We concluded that water shortages act to weaken the growth and propagation of H. rhamniodes plantations.

An improved apparent permeability model considering full pore pressure range,variable intrinsic permeability and slippage coefficient

Although the slippage effect has been extensively studied,most of the previous studies focused on the impact of the slippage effect on apparent permeability within a low pore pressure range,resulting in the inability of matching the evolution of permeability in the remaining pressure range.In this paper,a new apparent permeability model that reveals the evolution of permeability under the combined action of effective stress and slippage in the full pore pressure range was proposed.In this model,both intrinsic permeability and slippage coefficient are stress dependent.Three experimental tests with pore pressure lower than 2 MPa and a test with pore pressure at about 10 MPa using cores from the same origin under constant confining stress and constant effective stress are conducted.By comparing experimental data and another apparent permeability model,we proved the fidelity of our newly developed model.Furthermore,the contribution factor of the slippage effect Rslip is used to determine the low pore pressure limit with significant slippage effect.Our results show that both narrow initial pore size and high effective stress increase the critical pore pressure.Finally,the evolutions of the slippage coefficient and the intrinsic permeability under different boundary conditions were analyzed.

A rocky hill on the continuous ejecta of Ziwei crater revealed by the Chang’e-3 mission

The Chinese Chang’e-3 mission landed close to the eastern rim of the ~450 m diameter Ziwei crater. Regional stratigraphy of the landing site and impact excavation model suggest that the bulk continuous ejecta deposits of the Ziwei crater are composed by Erathothenian-aged mare basalts. Along the traverse of the Yutu rover, the western segment features a gentle topographic uplift(~0.5 m high over ~4 m), which is spatially connected with the structurally-uplifted crater rim. Assuming that this broad topographic uplift has physical properties discontinuous with materials below, we use data returned by the high-frequency lunar penetrating radar onboard the Yutu rover to estimate the possible range of relative permittivity for this topographic uplift. Only when the relative permittivity is ~9 is the observed radar reflection consistent with the observed topography, suggesting that the topographic uplift is composed of basaltic blocks that were excavated by the Ziwei crater. This result is consistent both with the impact excavation model that predicts deeper basaltic materials being deposited closer to the crater rim, and with observation of numerous half-buried boulders on the surface of this hill. We note that this study is the first to use topography and radargram data to estimate the relative permittivity of lunar surface uplifts, an approach that has had many successful applications on Mars. Similar approaches can apply other ground penetrating radar data for the Moon, such as will be available from the ongoing Chang’e-4 mission.

Formation mechanism of the Lidang circular structure in the Guangxi Province

The Lidang circular structure in the center of the Guangxi Province is about 8 km in diameter. This structure appears as an abnormal shallow depression that has disturbed the rather harmonic regional joint systems. Its unique occurrence in the whole region, the circular morphology, negative topography, and the spatial distribution of interior and exterior strata are all consistent with those of impact craters that are formed by asteroidal or cometary collision. To test the impact hypothesis, we carried out both field investigation and remote sensing study of this structure. Regional geological history suggests that if the impact hypothesis were correct, the impact event should have occurred at or after the Early Permian. Field investigation found that the strata inside and outside the crater are dominated by parallel stacks of Lower and Upper Permian limestone that have various thicknesses and different mud contents. The layers of limestone within and outside the circular structure have identical attitudes;no structural disturbances were visible in the outcrops. Field investigations provide conclusive evidence against the impact cratering hypothesis. A high-resolution digital elevation model shows that the spatial distribution of rounded mountains within the structure is controlled by faint but continual extension of joints, suggesting that the crater interior has gone through a much higher degree of erosion. Therefore, regional joints that had once existed within the crater are preserved less well than exterior terrains, forming the abruptly disrupted circular depression. Differential erosion, as the possible formation mechanism of the Lidang structure, is consistent with the different mud contents found between the interior and exterior limestone. The circular outline of this structure may correspond to the shape of the original deposition basin. In conclusion, the Lidang circular structure is a polje formed by karstification, not an astrobleme.

An updated constraint on the local stratigraphy at the Chang'E-4 landing site

The Chang’E-4 mission has been exploring the lunar farside.Two scientific targets of the rover onboard are(1)resolving the possible mineralogy related to the South Pole-Aitken basin and(2)understanding the subsurface processes at the lunar farside.Publications to date that are based on the reflectance spectra and radar data obtained by the rover have shown a persistent inconsistency about the local stratigraphy.To explain both the abnormal surface topography at the landing site and the unexpected radargram observed by the rover,the Alder crater has been frequently reported to be older than the mare basalts at that landing site.However,this argument is not supported by earlier geological mapping nor recent crater statistics.Resolving this controversy is critical for a full understanding of the geological history of the landing area and for correct interpretations of the scientific data returned.Employing detailed crater statistics,rigorous statistical analyses,and an updated crater chronology function,this study is determined to resolve the relative ages of the Alder crater,Finsen crater,and the mare basalts on the floor of Von Kármán.Our results reveal that while background secondaries and local resurfacing have widely occurred in the study area,affecting age determinations,the statistics are significant enough to conclude that the Alder crater is the oldest among the three targets.This independent constraint is consistent with both the crosscutting relationships of different terrains in this area and global stratigraphic mapping.Our results exclude Alder as a possible contributor of the post-mare deposits at the landing site,appealing for a more systematic stratigraphy study to resolve the provenances of these deposits.

Fine debris flows formed by the Orientale basin

The prototype for investigations of formation mechanisms and related geological effects of large impact basins on planetary bodies has been the Orientale basin on the Moon.Its widespread secondaries,light plains,and near-rim melt flows have been well mapped in previous studies.Flow features are also widely associated with secondaries on planetary bodies,but their physical properties are not well constrained.The nature of flow features associated with large impact basins are critically important to understand the emplacement process of basin ejecta,which is one of the most fundamental processes in shaping the shallow crusts of planetary bodies.Here we use multisource remote sensing data to constrain the physical properties of flow features formed by the secondaries of the Orientale basin.The results suggest that such flows are dominated by centimeter-scale fine debris fines;larger boulders are not abundant.The shattering of target materials during the excavation of the Orientale basin,landing impact of ejecta that formed the secondaries,and grain comminution within the flows have substantially reduced particle sizes,forming the fine flows.The discovery of global-wide fine debris flows formed by large impact basins has profound implications to the interpretation of both previously-returned samples and remote sensing data.

Geological Context of the SLIM Landing Site

INTRODUCTION Japan’s first successful lunar landing mission,Smart Lander for Investigating Moon(SLIM),was landed on the Moon on January 19th,2024.SLIM made a precise landing within 100 m of the targeted landing zone(central coordinates 13.316°S,25.251°E),which is located around the Shioli crater(D=270 m,central coordinates as 13.33°S,25.23°E)in the southwestern ejecta of the Theophilus crater(D=98.6 km,central coordinates as 11.45°S,26.28°E).

Volcanism in the Solar System

Volcanic activity is the main process for heat-material exchange and circulation for differentiated planets. All terrestrial planets in the Solar System, the Moon, the satellites of giant planets, and the dwarf planets once experienced or are currently experiencing volcanic activities. This paper summarized the volcanism(main volcanic features and their formation) on the Moon, Mars, Venus, and Mercury in the inner Solar System, volcanism and cryovolcanism on satellites(Io, Europa,Enceladus) of giant planets, as well as volcanism on dwarf planets including Cere in the main asteroid belt and Pluto in the Kuiper belt. This work shows volcanism in the Solar System is driven by various factors, forming abundant volcanic landforms.It has significant meanings to compare volcanism happening on different planets using comparative planetology approaches for a better understanding of volcanism, the planetary habitability, and the information contained on the origin and evolution of planets in the Solar System.

月球南极—艾特肯盆地的形成与早期撞击历史

月球撞击构造完整地记录了内太阳系的小天体撞击历史,是研究撞击历史和撞击通量的最好样本。南极—艾特肯(SPA)盆地是月球上最大最古老的撞击盆地,其形成时间是重建月球演化历史的关键节点。SPA盆地的形成与早期撞击历史的研究,对于揭示月球外动力演化历史、建立月球演化的精确时间标尺、理解太阳系天体轨道动力学演化以及地球宜居环境演化等具有重大科学意义,是月球科学的突破口之一。本文梳理了SPA盆地等早期重大撞击事件的形成时间、SPA盆地的形成过程及全球响应、早期小天体的撞击通量等关键科学问题。提出了在月球科研站任务背景下的研究建议,并倡议采样返回与样品定年、遥感数据撞击坑统计分析、撞击成坑数值模拟相结合的研究方法。

Subsurface Structures at the Chang'e-3 Landing Site: Interpretations from Orbital and In-Situ Imagery Data

The Chang＇e-3（CE-3） spacecraft successfully landed on one of the youngest mare surfaces on the Moon in December 2013. The Yutu rover carried by CE-3 was equipped with a radar system that could reveal subsurface structures in unprecedented details, which would facilitate understanding regional and global evolutionary history of the Moon. Based on regional geology, cratering scaling, and morphological study, here we quantify the subsurface structures of the landing site using high-resolution orbital and in-situ imagery data. Three layers of lunar regolith, two layers of basalt units, and one layer of ejecta deposits are recognized at the subsurface of the landing site, and their thicknesses are deduced based on the imagery data. These results could serve as essential references for the on-going interpretation of the CE-3 radar data. The ability to validate our theoretical subsurface structure using CE-3 in-situ radar observations will improve the methods for quantifying lunar subsurface structure using crater morphologies and scaling.

月球上发现半透明玻璃球

利用嫦娥四号月球探测任务玉兔二号月球车获取的全景相机数据,在巡视路线上附近发现了数粒直径达2.5 cm的半透明玻璃球.这是首次在月球上发现手标本尺度大小的透明玻璃球.区域地质研究和撞击破碎模型对比表明这些玻璃球不是火山玻璃或降落至月面的陨石,而是形成在月球上的撞击玻璃.对比典型的月球岩石的化学成分及其熔体在冷凝时成核结晶的临界降温速率,发现月球玄武岩和其他富铁的岩石不是形成这些撞击玻璃的原岩.斜长岩熔体的临界降温速率极低,在月球环境下冷凝时足以形成直径高达5 cm的透明/半透明玻璃球.基于高能远撞击玻璃的成因机理,结合嫦娥四号着陆点附近1 km/s的上限弹道溅射距离中的矿物和元素含量数据,发现很多撞击事件足以形成此类撞击玻璃.这些撞击玻璃记录了重要的撞击过程和早期撞击历史的信息,是未来月球探测的重要采样目标.

Preface: Joint researches are benefiting the Chang’E-1 comprehensive lunar scientific studies which probe ever deeper

Payloads of the first Chinese lunar mission Chang’E-1 obtained fruitful scientific data which cover a wide range of disciplines and fields.

Impact Craters with Circular and Isolated Secondary Craters on the Continuous Secondaries Facies on the Moon

On airless bodies such as the Moon and Mercury, secondary craters on the continuous secondaries facies of fresh craters mostly occur in chains and clusters. They have very irregular shapes. Secondaries on the continuous secondaries facies of some Martian and Mercurian craters are more isolated from each other in distribution and are more circular in shape, probably due to the effect of target properties on the impact excavation process. This paper studies secondaries on the continuous secondaries facies of all fresh lunar complex craters using recently-obtained high resolution images. After a global search, we find that 3 impact craters and basins on the Moon have circular and isolated secondaries on the continuous secondaries facies similar to those on Mercury： the Orientale basin, the Antoniadi crater, and the Compton crater. The morphological differences between such special secondaries and typical lunar secondaries are quantitatively compared and analyzed. Our preliminary analyses suggest that the special secondaries were probably caused by high temperature gradients within the local targets when these craters and basins formed. The high-temperature of the targets could have affected the impact excavation process by causing higher ejection angles, giving rise to more scattered circular secondaries.

Non-Impact Origin of the Baisha Structure in Hainan Province, China

The Baisha Structure,with a rim-to-rim diameter of^3.7 km,in the center of the Hainan Province,southern China has been considered to be an impact crater.Field investigation and petrological study are presented in this paper to investigate the impact hypothesis for this structure.The^600-m-thick Lower Cretaceous feldspathic quartz sandstones from the Lumuwan Formation are the major outcrops both within and outside of the structure.The amphitheater-shaped rim of the structure is composed of granite porphyries that are intruded in the Lumuwan Formation.Previously interpreted impact breccia and impact melt rocks are actually granite porphyries different cooling rates and weathering status.Rocks from locations that most likely have recorded shock metamorphic signatures are sampled,but petrographic analyses reveal no indications of shock metamorphism.While subtle structural deformation occurs at the contact boundary between the granite porphyries and the feldspathic quartz sandstones,the feldspathic quartz sandstones exhibit uniformed dipping strata across the crater floor and walls.All the evidence suggests that the Baisha Structure was not formed by impact cratering.It most likely has been shaped by a combination of magmatic intrusion and long-term differential erosion.