易漏失地层承压能力分析

随着各种复杂地质条件下勘探井作业数量的增多和井深的不断加大，因漏失引起的复杂情况不断增多。为了顺利钻达设计深度，施工中常常需要采用人工承压手段检验和提高上部地层承压能力，以便能用较高密度的钻井液钻至较深的地层。实际的承压作业中，往往会遇到反复承堵但无法提高承压能力的情况，即现场常说的地层抗破裂强度不够。结合现场实践经验，对室内实验结果进行的综合分析表明，地层的承压能力与裂缝的变化情况直接相关，并受裂缝分布形式和分布范围的影响，当裂缝波及范围较小时，处理时应尽可能形成较厚的封堵层；当裂缝波及范围较大时，则应首先在漏失通道中形成阻流带，再尝试采用其他手段逐渐提高承压能力。同时分析了室内模拟实验结果与现场应用结果的差异，探讨了造成差异的原因。

Analysis on pressure-bearing capacity of leakage formation

The down-hole troubles caused by circulation loss are more and more while the operation amount and well depth of exploration increase under the complicated geological conditions. The sealing under pressure technology was used to check the pressure-bearing capacity of upper formation and to meet the depth as far as possible using the high-density drilling fluids. In the practice of drilling, the sealing ability under pressure is not often improved after field operation, because the formation resistance to rupture is not enough high. The field experience and laboratory test show that the sealing ability under pressure is directly related with the aperture and distribution of fractures. If the spread range of fracture is small, a thicker sealing wall should be made. If the spread range of fracture is big, the chock zone should be firstly formed in the loss circulation zone, and then other means should be taken to improve the sealing ability under pressure. The difference of the technology applied in laboratory simulation test and field practice was analyzed. The reasons resulting in the difference were discussed.