We present a systematic model that links the generation, migration, phase partitioning, and accumulation of methane into a closed loop as the sediment is deposited from the seafloor and buried through the base of hydrate stability zone (BHSZ). In our model, methane is generated by biodegradation of organic carbon in muds. Hydrate does not form and methane is not trapped until a coarse-grained layer is deposited, because the small pores prevent hydrate formation in muds. Instead, methane diffuses into sands/silts where methane solidifies into hydrate. As hydrate-bearing sands/silts pass through the BHSZ during sediment burial, methane hydrate dissociates, and releases free gas. The released and the newly generated free gas below the BHSZ concentrates into a vertical/dipping zone with low capillary entry pressure and high permeability and flows upward driven its buoyancy. When free gas reaches the hydrate stability zone (HSZ), capillary forces drive free gas to flow laterally, preferentially enter sands/silts, feed hydrate growth, and elevate hydrate saturation. With three-dimensional focused free gas flow, microbial methane that is generated from a much larger fetch area of the entire basin, both above and below the BHSZ, is concentrated into coarse-grained layers at structural closures for hydrate formation. Our model illustrates how geological evolution, microbial methane generation, and gas flow by buoyancy couple to generate concentrated hydrate deposits in geological system. These insights can be used to explore for high-concentration methane hydrate and are important for understanding the methane budget and carbon cycle under the seafloor.

中文翻译：

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三维自由气流将全盆地微生物甲烷集中到地质系统中的浓缩甲烷水合物储层

我们提出了一个系统模型，该模型将甲烷的生成、迁移、相分配和积累连接到一个闭环中，因为沉积物从海底沉积并埋入水合物稳定带 (BHSZ) 底部。在我们的模型中，甲烷是通过泥浆中有机碳的生物降解产生的。在粗粒层沉积之前，不会形成水合物，也不会捕获甲烷，因为小孔阻止了泥浆中水合物的形成。相反，甲烷扩散到沙子/淤泥中，在那里甲烷固化成水合物。当含水合物的砂/粉砂在沉积物掩埋过程中穿过 BHSZ 时，甲烷水合物分解并释放出游离气体。BHSZ下方释放的和新生成的游离气体集中到一个具有低毛细管入口压力和高渗透率的垂直/倾斜区，并向上流动驱动其浮力。当游离气到达水合物稳定带 (HSZ) 时，毛细管力驱动游离气横向流动，优先进入砂/粉砂，促进水合物生长，提高水合物饱和度。通过三维聚焦自由气流，从整个盆地更大的提取区域（BHSZ 上方和下方）产生的微生物甲烷在结构闭合处集中成粗粒层，以形成水合物。我们的模型说明了地质演化、微生物甲烷生成和浮力偶气体流动如何在地质系统中生成集中的水合物沉积物。