浮力作用对大斜度井套管居中度的影响

摘要

准确了解套管内外密度差所产生的浮力对套管居中度的影响对于大斜度井合理安放扶正器,降低套管下入风险具有重要的意义.通过对扶正器受力分析模型进行修正,建立了套管内外密度差对套管居中度的影响图版,同时考虑顶替过程中套管内外密度差随时间变化情况,形成埕海油田大斜度井套管扶正器安放方法.计算结果表明,埕海地区扶正器安放间距分别为30 m、20 m、15 m时,通过浮力作用使套管居中度最大可增加36.4%、19.6%、12.2%,井斜角越大、套管内外密度差越大,居中度变化值越大.扶正器安放间距为10 m时,浮力作用减弱,居中度变化值最大仅为6.2%.研究结果表明,扶正器安放间距、井斜角的正弦值、套管内外密度差与浮力作用下的居中度变化量呈三次多项式的非线性正相关.ZH29-30井实践表明,考虑浮力作用的套管居中度设计方法,可以有效提高固井顶替效率,保证套管安全下入.%In order to install centralizers in high angle deviated wells rationally and decrease the risk of casing running, it is sig-nificant to figure out accurately the effect of buoyance generated by the difference of density inside and outside the casing on the casing central degree. In this paper, the model for analyzing the forces on centralizers was modified and a chart describing the influence of den-sity difference between inside and outside the casing on the casing central degree was established. And the change of density difference between inside and outside the casing over the time in the process of displacement was also taken into consideration. Thus, the central-izer installation method for high angle deviated wells in Chenghai Oilfield was developed. Calculation results show that the maximum increment of casing central degree due to buoyance is 36.4%, 19.6% and 12.2% when the centralizer installation spacing in the area of Chenghai is 30 m, 20 m and 15 m. The higher the hole deviation angle is and the higher the density difference between inside and outside the casing is, the larger the variation of central degree is. When the centralizer installation spacing is 10 m, buoyance gets weak and maximum variation of central degree is only 6.2%. It is in nonlinear positive correlation of cubic polynomial between centralizer installation spacing, sine of hole deviation angle, density difference between inside and outside the casing and central degree variation under the effect of buoyance. It is shown from the practice in Well ZH29-30 that the casing central degree design method which takes the buoyance into account can improve the displacement efficiency of cementing and ensure the safe running of casing.