钻井工程中沥青与钻井液动态置换规律实验研究

钻井工程中钻遇活跃沥青层时,涌漏并发等恶性事故严重影响钻井作业的正常进行。针对中东Y油田沥青层钻井面临的严重钻井液漏失与沥青侵入问题,首先分析了沥青层特征和钻井液漏失特点,发现沥青与钻井液间的重力置换是钻井液漏失和沥青侵入的主要原因。研制了可视化沥青-钻井液动态置换模拟实验装置,分别在钻井液循环和静止状态下,模拟研究了钻井工程中钻井液与沥青的动态置换过程,分析了钻井液密度和黏度、地层裂缝宽度以及沥青黏度对置换过程的影响规律。结果表明,随着钻井液密度增加,沥青置换量呈对数增大趋势;随着地层裂缝宽度增加,置换量呈线性增大趋势;随着沥青黏度增加,置换量呈对数减小趋势;而钻井液黏度与置换量呈负相关关系。因此,钻井作业中,需合理控制钻井液密度以平衡地层压力;适当提高钻井液黏度;重点加强钻井液随钻堵漏作用,有效封堵地层裂缝,减少和堵塞钻井液漏失与沥青侵入井筒的通道。结合控压钻井技术,在该方法的指导下后续钻井作业中顺利钻穿沥青层。

Experimental research on dynamic replacement of asphalt and drilling fluid in drilling engineering

Serious accidents may occur such as lost circulation when drilling in active bitumen layer, which will significantly affect the operations. We analysed the features and characteristics of bitumen layer and drilling fluid leakage, and found gravity displacement between bitumen and drilling fluid is the main reason for problems of leakage and bitumen intrusion in Y Oilfield in the Middle East. A visualized test device for simulating bitumen-drilling fluid dynamic replacement was developed. We studied the replacement process respectively under circulation and static state by using this device, analysed the influence of drilling fluid density and viscosity, formation fracture width and bitumen viscosity on replacement. The results show that displacement quantity of bitumen showed a logarithmic increase and a linear increase respectively with increasing of drilling fluid density and fracture width, but logarithmically decreased when bitumen viscosity decreased. The viscosity of drilling fluid was negatively correlated with the displacement quantity. As a result, it is necessary in drilling process to control the fluid density to balance formation pressure and properly improve the fluid viscosity. We must attach importance on the effect of sealing while drilling as it can effectively plug formation fracture, block and reduce lost and intrusion channels. Instructed by our research results and combined with managed pressure drilling(MPD) technology, bitumen layer was drilled through successful in field test.