@article{LiSpangenbergSchicksetal.2022, author = {Li, Zhen and Spangenberg, Erik and Schicks, Judith Maria and Kempka, Thomas}, title = {Numerical simulation of hydrate formation in the LArge-Scale Reservoir Simulator (LARS)}, series = {Energies : open-access journal of related scientific research, technology development and studies in policy and management}, volume = {15}, journal = {Energies : open-access journal of related scientific research, technology development and studies in policy and management}, number = {6}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {10.3390/en15061974}, pages = {27}, year = {2022}, abstract = {The LArge-scale Reservoir Simulator (LARS) has been previously developed to study hydrate dissociation in hydrate-bearing systems under in-situ conditions. In the present study, a numerical framework of equations of state describing hydrate formation at equilibrium conditions has been elaborated and integrated with a numerical flow and transport simulator to investigate a multi-stage hydrate formation experiment undertaken in LARS. A verification of the implemented modeling framework has been carried out by benchmarking it against another established numerical code. Three-dimensional (3D) model calibration has been performed based on laboratory data available from temperature sensors, fluid sampling, and electrical resistivity tomography. The simulation results demonstrate that temperature profiles, spatial hydrate distribution, and bulk hydrate saturation are consistent with the observations. Furthermore, our numerical framework can be applied to calibrate geophysical measurements, optimize post-processing workflows for monitoring data, improve the design of hydrate formation experiments, and investigate the temporal evolution of sub-permafrost methane hydrate reservoirs.}, language = {en} } @article{LiSpangenbergSchicksetal.2022, author = {Li, Zhen and Spangenberg, Erik and Schicks, Judith Maria and Kempka, Thomas}, title = {Numerical Simulation of Coastal Sub-Permafrost Gas Hydrate Formation in the Mackenzie Delta, Canadian Arctic}, series = {Energies}, volume = {15}, journal = {Energies}, number = {14}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {10.3390/en15144986}, pages = {25}, year = {2022}, abstract = {The Mackenzie Delta (MD) is a permafrost-bearing region along the coasts of the Canadian Arctic which exhibits high sub-permafrost gas hydrate (GH) reserves. The GH occurring at the Mallik site in the MD is dominated by thermogenic methane (CH4), which migrated from deep conventional hydrocarbon reservoirs, very likely through the present fault systems. Therefore, it is assumed that fluid flow transports dissolved CH4 upward and out of the deeper overpressurized reservoirs via the existing polygonal fault system and then forms the GH accumulations in the Kugmallit-Mackenzie Bay Sequences. We investigate the feasibility of this mechanism with a thermo-hydraulic-chemical numerical model, representing a cross section of the Mallik site. We present the first simulations that consider permafrost formation and thawing, as well as the formation of GH accumulations sourced from the upward migrating CH4-rich formation fluid. The simulation results show that temperature distribution, as well as the thickness and base of the ice-bearing permafrost are consistent with corresponding field observations. The primary driver for the spatial GH distribution is the permeability of the host sediments. Thus, the hypothesis on GH formation by dissolved CH4 originating from deeper geological reservoirs is successfully validated. Furthermore, our results demonstrate that the permafrost has been substantially heated to 0.8-1.3 degrees C, triggered by the global temperature increase of about 0.44 degrees C and further enhanced by the Arctic Amplification effect at the Mallik site from the early 1970s to the mid-2000s.}, language = {en} } @article{LiWangHerzschuhetal.2022, author = {Li, Zhen and Wang, Yongbo and Herzschuh, Ulrike and Cao, Xianyong and Ni, Jian and Zhao, Yan}, title = {Pollen-based biome reconstruction on the Qinghai-Tibetan Plateau during the past 15,000 years}, series = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, volume = {604}, journal = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0031-0182}, doi = {10.1016/j.palaeo.2022.111190}, pages = {12}, year = {2022}, abstract = {Reconstruction of past vegetation change is critical for better understanding the potential impact of future global change on the fragile alpine ecosystems of the Qinghai-Tibetan Plateau (QTP). In this paper, pollen assemblages comprising 58 records from the QTP, spanning the past 15 kyrs, were collected to reconstruct biome compositions using a standard approach. Six forest biomes were identified mainly on the southeastern plateau, exhibiting a pattern of gradual expansion along the eastern margin during early to mid-Holocene times. The alpine meadow biome was separately identified based on an updated scheme, and showed notable westward expansions towards lower latitudes and higher altitudes during early Holocene times. Consistent patterns of migration could also be identified for the alpine steppe biome, which moved eastward during the late Holocene after 4 ka. As the dominant biome type, temperate steppe was distributed widely over the QTP with minor migration patterns, except for a progressive expansion to lower altitudes in the late Holocene times. The desert biome was inferred mainly as covering the northwestern plateau and the Qaidam Basin, in relatively restricted areas. The spatial distribution of the reconstructed biomes represent the large-scale vegetation gradient on the QTP. Monsoonal precipitation expressed predominant controls on the development of alpine ecosystems, while the variations in desert vegetation responded to regional moisture brought by the mid-latitude Westerlies. Temperature changes played relatively minor roles in the variations of alpine vegetation, but exerted more significant impacts on the forest biomes.}, language = {en} }