温-压作用下水泥环缺陷对套管应力的影响

Influence of Cement Sheath Defect on Casing Stress under Temperature-pressure Effect

在页岩气水平井多级分段压裂施工中,由于压裂段固井质量较差,当井筒温度和压力急剧变化时,套管失效风险会大大增加。在现场完井和压裂施工数据基础之上,综合考虑压裂压力和井底温度变化,建立了不同水泥环形态的套管-水泥-地层组合体模型,研究压裂过程中水泥环缺失、压裂压力和温度变化对套管应力的影响。计算结果表明:压裂施工中,当以大排量向井筒内泵入压裂液时,井底温度显著降低;如果施工压力较大、水泥环出现窜槽缺失,则套管会产生应力集中,这将急剧增加套管应力,大大增加套管失效风险。固井质量对井筒完整性至关重要,同时必须将压裂液温度、排量和施工压力控制在合理范围,从而保证压裂过程中套管的安全。

In the multistage fracturing of shale gas horizontal wells,owing to the poor cement quality,the risk of casing failure will greatly increase under the sharp change of wellbore temperature and pressure.Based on the field completion and hydraulic fracturing data,and considering downhole pressure and temperature changes during fracturing,the casing-cement-formation models with different cement sheath shapes are established to study the effect of cement sheath defect,pressure and temperature on the casing stress.The calculation results show that,when the fracturing fluid is pumped into the wellbore with large displacement,the downhole temperature could be significantly reduced.Stress concentration could occur under the condition of high operation pressure and cement sheath defect,which could dramatically increase the casing stress,resulting in increased risk of casing failure.Cementing quality is critical to the integrity of the wellbore.The fracturing fluid temperature,displacement,and operation pressure must be controlled within a reasonable range to ensure the safety of the casing during fracturing.