多层组合套管特性分析

MULTIPLE COMBINATION CASING CHARACTERISTIC ANALYSIS

地层蠕变效应是引起套管大量损坏的主要原因之一,而解决此问题的有效途径之一是采用组合套管。文章通过引入柔度系数的概念,给出了任意多层组合套管压力传递系数的规准表达形式,同时,假设地层为粘弹性的,导出了多层组合套管的地层蠕变附加载荷计算公式。分析了双层组合套管的各尺寸对套管抗挤能力的影响,研究了套管层数与套管抗挤能力的关系。数值计算结果表明,尽管随着套管的层数增加地层的蠕变载荷增大,但是内管所承担的最大蠕变载荷仍将单调下降,不论是单层套管还是多层套管,地层进水后都将增大其危险性。文中所提供压力传递系数和粘弹性地层蠕变附加荷载计算公式可供多层套管设计参考。

The formation creep effect caused by various reasons can produce an additional external pressure acting on casing well, and this pressure is much greater than the formation fluid pressure designed initially for the casing. The investigation results indicated that the formation creep effect was one of the main factors making the casing being greatly damaged, and one of the effective ways of solving such a problem was to adopt combination casing. In the paper, the standard expression of the pressure transfer coefficients of arbitrary multiple combination casing is put forward through introducing the concept of flexibility factor; if the formation is viscoelastic, the formulas of calculating the formation creep additional load of the multiple combination casing are derived; the effects of various dual combination casing sizes on collapse resistance are analyzed; and the relation between the number of casing layer and the casing collapse resistance is studied. According to the calculation results, it is shown that, although the formation creep load increases along with the increase in the number of casing layers, the maximum creep load borne by the inner tube will still monotonously decrease; and the danger of the casing, whether it is single-layer of multilayer casing, will increase after the water invading into the formation. The pressure transfer coefficients and calculation formulas of viscoelastic formation creep additional load mentioned in the paper may be available for reference to multiple casing design.