裂缝性地层承压堵漏模型研究及应用*

裂缝性地层承压能力低,承压堵漏难度高。为了解决该难题,从裂缝承压失稳机理出发,建立了考虑封堵层和裂缝扩展的承压堵漏新模型,分析了影响承压的关键因素,据此指导研发了高承压堵漏配方,形成了新型交联成膜堵漏技术,并开展了现场应用。研究表明,裂缝承压失稳包含封堵层失效和裂缝扩展两种形式；裂缝性地层承压能力由封堵层承压和裂缝扩展共同决定；提高承压能力要求堵漏材料抗压强度高,封堵层摩擦系数大、弹性变形率高、渗透率低,封堵层尽量封至缝口及封堵层厚度适中；新型交联成膜堵漏配方对1~5mm宽的裂缝,封堵层承压可达20MPa,抗返吐达3MPa以上,现场应用显著提高了地层承压能力。表明,承压堵漏模型具有较好的适用性,能够有效指导现场施工,为承压堵漏技术的研发提供了理论依据。

Wellbore strengthening model and its application in fractured formation

The pressure bearing capacity of fractured formation is narrow, lost circulation is more likely.In order to solve the problem of improving the pressure bearing capacity of fractured formation, the wellbore strengthening model was established, the key factors influencing the bearing capacity were analyzed, and a new cross-link plug technology was developed. Results show that the reasons of wellbore strengthening failure are sealing plug instability or fracture propagation. The pressure bearing capacity of fractured formation is determined by the bearing pressure of sealing plug and the fracture propagation pressure. To get high pressure bearing capacity, lost circulation materials demands high strength, high friction coefficient, high elastic deformation rate, low permeability, sealing plug position demands close to fracture mouth, and the sealing plug thickness need be moderate. The cross-linked plugging technique can significantly improve the positive bearing pressure and reversed bearing pressure of sealing plug. Experimental results show the positive bearing pressures can up to 20MPa, and the reversed bearing pressures are greater than 3MPa for 1-5 mm fractures. Field applications show that the model has good applicability, and it can be used to guide field applications effectively. The model provides a theoretical reference for wellbore strengthening in fractured formation.