Abstract Sand production encountered in the 2013 offshore field gas production tests at the Nankai Trough, Japan, could be attributed to well failure during reservoir compaction. In this study, well integrity under various reservoir compaction patterns for the Nankai Trough case is examined using a well-formation finite element model. The modelling details include the inclusion of a cement sheath as well as the modelling of construction processes (such as cement shrinkage). Well elongation in the overburden layer becomes significant when the reservoir subsidence is localized near the wellbore under large depressurization. Results show that the maximum plastic deviatoric strain level in the cement could reach 0.7% when the maximum reservoir subsidence reaches 0.85 m and cement shrinkage is limited. When cement shrinkage rises to 0.75%, the maximum plastic deviatoric strain increases to 2.4% as the cement accumulates additional plastic strain during shrinkage due to its deformation being constrained by the casing. In order to prevent the cement from failure, it might be effective to hold the pressure drawdown at a low level (e.g., several MPa) until the hydrate dissociation front advances to a certain radius from the well (e.g., a couple of tens of metres).

中文翻译：

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海上松散含甲烷水合物地层储层压实过程中轴向拉伸井变形模拟

摘要 2013年日本南海海槽海上油田采气试井出砂，可能是由于储层压实过程中的井故障。在这项研究中，使用井地层有限元模型检查了南海海槽在各种储层压实模式下的井完整性。建模细节包括包含水泥环以及施工过程（例如水泥收缩）的建模。当储层沉降位于井眼附近且在大减压下时，上覆层中的井伸长变得显着。结果表明，当储层最大沉降达到0.85 m且水泥收缩受限时，水泥中的最大塑性偏应变水平可达0.7%。当水泥收缩率上升到0.75%时，最大塑性偏应变增加到 2.4%，因为水泥在收缩过程中由于其变形受到套管的限制而积累了额外的塑性应变。为了防止水泥破裂，将压降保持在较低水平（例如几 MPa）可能是有效的，直到水合物分解前沿推进到距井一定半径（例如，几十米）。 ）。