Abstract Currently, the wellbore strengthening mechanism has not been fully understood, especially for the fracture network loss of the drilling fluid. In view of this, a new analytical model was established to discover the wellbore strengthening mechanism, considering the fracture network loss of the drilling fluid. In this model, the additional stress induced by the natural fracture network was calculated based on the fracture mechanics, and the fluid pressure distribution within the fracture network during the drilling fluid loss was investigated considering the fracture roughness. Especially, the wellbore strengthening mechanism was revealed, by comparing the stress intensity factors before and after the wellbore strengthening. The proposed analytical model was verified by comparing its results to those one of the numerical model. The comparison was focused on four aspects, namely, the fracture pressure, the fracture width, the stress acting on the fracture and the stress intensity factor. The maximum difference between the analytical and numerical results is within 5.45%. Additionally, the results show that the stress intensity factor obviously decreases after the wellbore strengthening. More importantly, the effect of the fracture roughness (JRC) on the fracture network loss was discussed. The results show that the fracture has a lower fracture pressure, a smaller fracture width and a smaller stress intensity factor with the increasing of JRC, which means that the fracture network with a higher JRC has a lower drilling fluid loss. Meanwhile, the effect of JRC on the wellbore strengthening was investigated, and the results show that the fracture with a higher JRC has the larger reduction for the fracture pressure, the fracture width and the stress intensity factor through operating the wellbore strengthening. This means that the fracture network with a larger JRC is better to operate the wellbore strengthening.

中文翻译：

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考虑裂缝粗糙度的钻井液缝网损失井筒加固新分析模型

摘要 目前，井筒强化机理尚未完全清楚，尤其是钻井液的裂缝网络损失。鉴于此，建立了一种新的分析模型，以发现井筒强化机制，考虑钻井液的裂缝网络损失。在该模型中，基于断裂力学计算了天然裂缝网络引起的附加应力，并考虑了裂缝粗糙度，研究了钻井液流失时裂缝网络内的流体压力分布。特别是通过对比井筒加固前后的应力强度因子，揭示了井筒加固机理。通过将其结果与数值模型之一进行比较，验证了所提出的分析模型。比较主要集中在裂缝压力、裂缝宽度、作用在裂缝上的应力和应力强度因子四个方面。分析结果和数值结果之间的最大差异在 5.45% 以内。此外，结果表明，井筒加固后应力强度因子明显降低。更重要的是，讨论了裂缝粗糙度（JRC）对裂缝网络损失的影响。结果表明，随着JRC的增加，裂缝具有较低的压裂压力、较小的裂缝宽度和较小的应力强度因子，这意味着具有较高JRC的裂缝网络具有较低的钻井液损失。同时研究了JRC对井筒加固的影响，结果表明，JRC越高的裂缝通过操作井筒加固对裂缝压力、裂缝宽度和应力强度因子的降低越大。这意味着具有较大 JRC 的裂缝网络更好地进行井筒加固。