稠油注蒸汽热采井套管柱预应力松弛效应分析

Analysis of the Casing String Pre-stressed Relaxation Effect in Heavy Oil Steam Injection Well

为了验证提拉预应力固井技术是否适合井深小于1 000 m的稠油热采注汽井,在280℃的高温蒸汽作用下,对热采N80H和普通N80Q两种套管进行了应力松弛试验;建立了套管-水泥环-地层全井筒平面有限元模型,进一步说明预应力固井技术在浅层稠油热采井中的作用。分析结果表明,稠油热采井在长期高温注蒸汽作业过程中,因管体应力松弛现象而致使预拉力失效;在高温作用下套管上施加的预拉力经过一定时间后会降低;提拉预应力固井对浅层稠油热采井没有效果,不能预防热应力导致的套管失效,建议在浅层稠油热采井中不采用预应力固井技术。

To verify whether lift pre-stressed cementing technology is suitable for heavy oil thermal recovery steam injection wells whose well depth is less than 1 000 m, the stress relaxation test was carried out with thermal recovery N80H casing and ordinary N80Q casing under the effect of 280 ~C steam. Meanwhile, in order to illustrate further the effect of pre-stressed cementing technology in shallow layer heavy oil thermal recovery wells, the finite element model of casing-cement sheath-formation overall wellbore plane was established, The analysis shows that pipe stress relaxation in heavy oil thermal recovery wells leads to failure of pre-tension force due to long-term high temperature steam injection operation. The pre-tension force applied to casing will decrease after a given time under the effect of high temperature. Lift pre-stressed cementing technology has no effect on heavy oil thermal recovery well. It cannot prevent casing failure caused by thermal stress. It is suggested that pre-stressed cementing technology should not be adopted in shallow layer heavy oil thermal recovery wells.