封堵技术基础理论回顾与展望

Review of basic theory for lost circulation control

以漏失控制机理为依据,将漏失控制理论分为刚性封堵理论、柔性封堵理论、减压防漏理论、提高地层承压能力理论和模糊封堵理论五类。封堵理论出现前,认为漏失因地层存在漏失通道所致,不考虑封堵材料与漏失通道匹配关系,发现漏失即尝试用封堵材料封堵;刚性封堵理论包括充填封堵理论和架桥封堵理论,认为刚性材料通过充填、架桥方式封堵漏失地层;柔性封堵理论认为,封堵材料随工作流体进入漏失通道,通过物理化学作用形成具有承压能力封堵带;减压防漏理论认为,降低液柱压力,减小与地层压力差,控制漏失驱动力实现防漏;提高地层承压能力理论,利用裂缝稳定机理封堵微裂缝,提高地层承压能力;模糊封堵理认为,漏失通道尺寸、数目和形状属模糊数学范畴,用物理化学作用下自然形成大小、数量和形状可变的封堵材料,以模糊封堵方式,封堵漏失通道。刚性封堵理论正融合其他理论快速发展,是目前防漏堵漏主流;减压防漏理论受地层、设备等条件较多限制,但发展迅速;模糊封堵理论以漏失通道和封堵材料自然属性相匹配为理念,可能成为封堵理论未来发展方向。

The theories for lost circulation control are divided into five major categories, including Rigid Plugging Theory, Flexible Plugging Theory, Lost Prevention by Lowering Pressure Theory, Lost Prevention by Bearing Pressure Theory, and Fuzzy Plugging Theory, based on plugging mechanisms. Before the emergence of plugging theories, the main causes of lost circulation were considered as the lost circulation medium, including fractures and caves in the formation. The medium was attempted to be blocked by plugging materials, without considering the size matching relationship between plugging materials and formation lost circulation medium. By Rigid Plugging Theory, including Packing Plugging Theory and Bridging Plugging Theory, the lost circulation is controlled by accumulating particles or bridging in the medium. By Flexible Plugging Theory, the lost circulation is controlled by the special properties of the polymer which invades the formation porous medium with working fluids and generates a special area to kill the lost circulation by physical and chemical reaction of some special ingredients. The Lowering Pressure Theory prevents lost circulation by lowering fluid column pressure to lower the pressure difference between bottomhole pressure and reservoir pressure. The Bearing Pressure Preventing Lost Theory plugs the micro-fractures to improve the bearing pressure capacity of wellbore, according to the principle of fracture stability. The Fuzzy Plugging Theory controls lost circulation by the particles, which are described by the fuzzy mathematics for the parameters of the pores and fractures such as size, shape, and number. Nowadays, the main plugging theory is Rigid Plugging Theory. The Lowering Pressure Prevention Lost Theory will not be used extensively since it is largely limited by formation and facilities, though it develops rapidly. The Fuzzy Plugging Theory may have a bright future for its compatibility between the natural formation and the property of the lost circulation materials.