裂缝网络地层钻井液漏失模拟

针对复杂裂缝性地层的钻井液漏失问题，基于蒙特卡罗随机建模理论，构建了三维离散裂缝网络地层模型。采用宾汉模式钻井液，建立了考虑裂缝线性变形的裂缝网络地层钻井液漏失模型，并利用有限元法求解该模型，对钻井液漏失行为进行模拟。研究表明，该模型可以进行裂缝内流速、漏失速率及漏失量等动态模拟；近井筒附近裂缝内钻井液流速较高，远离井筒处裂缝内流速较低；经过对数变换后，钻井液漏失速率曲线具有明显的无规律波动现象，与单条裂缝的漏失存在明显区别，可以用于识别裂缝网络地层；裂缝应力敏感性对漏失影响较大，考虑应力敏感性后，钻井液漏失量增加；数值模拟得到的漏失量与理论漏失量十分接近，证实模型可靠度高。现场应用表明，研究成果可有效识别出裂缝网络漏失，并以此采取了合理的堵漏技术方案，堵漏一次成功。 

Simulation of Mud Loss in Formations with Fracture Network

Based on the Monte Carlo random modeling theory, a 3-D discrete fracture network formation model has been established in an effort to solve the mud loss problem taking place in complex fractured formations. Using the Bingham model drilling fluid, a model describing the mud losses in networked fracture formations was established. This model took into consideration the linear deformation of the fractures. The model was calculated using finite element method to simulate the behavior of mud losses. Studies showed that this model was able to dynamically simulate the flowrate, rate of mud losses and total volume of mud losses inside a fracture. In fractures that were near the borehole wall, the mud flowrate was high, while in fractures that were far from the borehole wall, the mud flowrate was low. After logarithm transformation, the rate of mud loss curve showed obvious irregular fluctuation phenomenon, quite different from the behavior of mud losses in a single fracture. This phenomenon can be used to identify a formation with networked fractures. The stress sensitivity of fractures had greater effect on mud losses. Taking into account the stress sensitivity, the volume of mud losses increased. The volume of mud losses calculated from numerical simulation was close to the theoretical volume of mud losses, indicating the high reliability of the model established. Field application showed that the studying results can be used to find out mud losses into networked fractures. A mud loss control program based on this study was successfully used in controlling a mud loss just in one shot.