The shallow burial of gas hydrates results in stratum settlement owing to pore pressure reduction and hydrate dissociation during depressurization. To understand this behavior in hydrate-bearing stratum, a numerical model for determining the nonlinear mechanical constitutive relation of hydrate-bearing sediments was developed based on the physical and mechanical properties of hydrate-bearing sediments. The model was compared with an ideal elastic–plastic model on the core scale. Furthermore, a model for stratum settlement during depressurization in horizontal wells in hydrate-bearing strata was also established. Variance and range analyses were conducted using an orthogonal design to explore the influences of various factors on the stratum settlement. The results show that when compared with the ideal elastic–plastic model, the established numerical model presents a higher accuracy when characterizing the deformation behaviors of hydrate-bearing sediments at different stress states. During exploitation from vertical wells, the stratum settlement center corresponds to the wellhead. However, in the horizontal well design, the upper strata of horizontal well sections also settle apart from the zones around the wellhead. The wellhead settlement of horizontal wells is attributed to the load-bearing effect of the upper strata and the compaction effect of the middle strata. The load on the wellhead decisively influences the wellhead settlement, which is positively correlated with the drawdown pressure, production time, and build angle rate but shows no obvious correlation with the length of horizontal wells. The drawdown pressure exerts the greatest influence on the settlement of the upper strata in horizontal well sections, and the influences of the production time and the length of the horizontal wells successively follow this.

中文翻译：

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天然气水合物储层水平井降压过程中的地层沉降

天然气水合物埋藏较浅，减压过程中孔隙压力降低，水合物分解，导致地层沉降。为了理解含水合物地层中的这种行为，基于含水合物沉积物的物理和力学特性，开发了一种用于确定含水合物沉积物非线性力学本构关系的数值模型。该模型在岩心尺度上与理想的弹塑性模型进行了比较。此外，还建立了含水合物地层水平井降压过程中地层沉降模型。采用正交设计进行方差和极差分析，探讨各种因素对地层沉降的影响。结果表明，与理想弹塑性模型相比，所建立的数值模型在表征不同应力状态下含水合物沉积物的变形行为时具有更高的精度。直井开采时，地层沉降中心与井口相对应。然而，在水平井设计中，水平井段的上层地层也与井口周围的区域分离。水平井井口沉降主要是由于上层地层的承重作用和中层地层的压实作用。井口载荷对井口沉降有决定性影响，与压降压力、生产时间、建斜率呈正相关，与水平井长度无明显相关性。