低荧光钻井液防塌封堵新材料及其作用机理

含微裂缝的硬脆性泥页岩地层发生井壁坍塌的主要诱因之一便是钻井液中的液相进入微裂缝，导致近井壁地带孔隙压力升高，地层强度降低之故，解决这类问题的最直接手段就是对微裂缝进行物理封堵。为防止井壁坍塌，研制了类似于沥青类的防塌封堵新材料SAL，并对其性能和封堵效果进行了实验分析。结果表明：该材料具有较低的荧光性及良好的抑制性，对钻井液的流变性及pH值影响较小；在浓度为3%，温度为120 ℃时封堵效果最好。进而在显微镜下观察了浓度3%的SAL在120 ℃情况下封堵20 μm微裂缝的微观封堵效果，发现其封堵机理与沥青类防塌封堵剂类似，在温度和压力作用下软化变形，进入微裂缝架桥、填充，在微裂缝的前端形成一层致密的封堵带，封堵带由SAL同黏土颗粒聚结在一起，形成了团状物，使得封堵带致密性大幅度提高，阻止钻井液中的液相进入微裂缝，从而达到了防塌的目的。

A novel low fluorescence anti sloughing agent for a drilling fluid system and its mechanism analysis

For hard and brittle shale formation with micro fractures, one of the major reasons for wellbore collapse is the liquid of the drilling fluid entering into the micro fractures, resulting in pore pressure rise near the wellbore and strength reduction of formation. Therefore, physically sealing the micro fractures is the most direct means for solving this problem. For this purpose, a novel anti sloughing agent SAL was developed similar to kerite, and experiments were performed for analyzing its performance and sealing effect, and the results showed that: i) the agent is of relatively low fluorescence and favorable inhibition; ii) the agent has a small impact on rheological property and pH value of drilling fluid; and iii) its sealing effect has an optimum performance at 120℃ with a concentration of 3%. SAL of 3% concentration was further observed at 120℃ for the microscopic effect of sealing 20 μm micro fractures, which indicated that its sealing mechanism is similar to that of a kerite anti sloughing agent. Specifically, SAL is softened and deformed under certain temperature and pressure, and then enters into the micro fractures; by bridging and filling, a layer of tight seal is formed in front of the micro fractures, which is coalesced with clay particles with SAL to form lumps. As a result, the seal compactness is significantly improved, preventing the liquid in drilling fluid from entering into the micro fractures, and finally realizing the anti sloughing effect.