基于压力平衡条件下“戴帽”固井注水泥技术探讨

Discussion of cement injection technology for “cap” cementation based on balanced pressure condition

摘要:

在地热井漏失地层进行“戴帽”固井注水泥难度大，往往因挤入的水泥浆偏离设计位置而导致固井失败。本文提出了漏失层“戴帽”固井的技术思路，即利用井内液柱压力与地层裂隙压力保持平衡以有效控制固井水泥浆柱移动位置，通过控制挤注排量以防止水泥浆被稀释。在具体实施中，可以采用开放固井和封闭固井两种方式。前者在注替浆过程中，井筒与外界大气、上下井筒之间始终相通。当上下套管级差较大时，水泥浆柱在平衡过程中下移距离较长，位置不易控制，且易稀释，但是所需工具简单，适合应用于上下套管级差较小的条件，尤其是在同级套管内。对于后者而言，需采用特殊密封工具封闭下部套管，在注替浆过程中，上下井筒始终是不通的。可以避免水泥浆柱下移距离长、位置不易控制、易稀释等缺点，适合各种套管级配条件下固井注水泥作业，在套管级差较大时更显其精确封固优势。

关键词:“戴帽”固井;压力平衡;开放固井;封闭固井;注水泥;地热井

Abstract:

It is difficult to “cap” cement in the lost circulation formation of geothermal wells. In most cases， the well cementation is failure due to the deviation of the squeezed cement slurry from the design position. In this paper， the technical idea of “cap” cementation in lost circulation zone is proposed， that is， the moving position of the cement slurry column is effectively controlled by balancing the fluid column pressure in the well with the formation fracture pressure， and the cement slurry is prevented from being diluted by controlling the displacement of squeeze injection. Open cementing and closed cementing methods can be both used in practice. The open cementing is suitable in the condition that the difference of the casing lever among the upper parts and the lower parts is small especially in same level. The shaft is always connected with the outside air and the upper and lower shaft always connected in the process of slurry injection. The cement slurry column moves down a long distance during the balancing process and is easily diluted， and the position of the slurry column is difficult to control when the upper casing is quite different from the lower one. However， the required tools are simple. The closed cementing is suitable for any casing matching requirements， especially for the larger casing grade difference. For this method， special sealing tools shall be used to seal the lower casing， the upper and lower wellbore are impassable during cementing， which could avoid the disadvantages of long downward distance of cement slurry column， difficult position control and easy dilution， etc.

Key words:“cap” cementation;pressure balancing;open cementing;closed cementing;cement injection;geothermal well