页岩气水平井低密度防窜水泥浆增稠机理

Thickening mechanism of low-density anti-channeling cement slurry in shale-gas horizontal wells

针对四川盆地涪陵页岩气加密井遇到地层漏、承压低问题,优化设计了一种以漂珠为主要减轻剂的低密度水泥浆体系,该体系具有浆体稳定、失水低、流变性好、稠化时间可控等优点。然而在稠化实验升温升压初始阶段,出现了稠度快速增大现象,为注水泥施工带来了安全隐患。通过稠化实验和流变实验分析导致浆体增稠的因素,探讨漂珠低密度水泥浆体系的增稠机理。结果表明:①导致漂珠低密度防窜水泥浆体系在升温升压阶段稠度增大的主要原因是漂珠破碎和抗压强度低,漂珠中的气泡溶入浆体中,增大了浆体的稠度;②基于漂珠低密度防窜水泥浆增稠机理,选择合适的强效消泡剂、流型调节剂和高强度漂珠可以减缓漂珠低密度防窜水泥浆体系初始稠度增大的程度,从而保证施工安全。

Most shale-gas infill wells in Fuling area are often suffered from formation leakage and low pressure.So,a kind of low-density cement slurry with hollow-microsphere,as the main lightening agent,was optimally designed,which has the advantages of good sedimentation stability,low fluid loss,good rheological property,and controllable thickening time.In the initial phase of temperature and pressure increase in thickening experiments,however,the consistency increased rapidly,which might bring about safety risks to cementing operation.Then,the factors leading to slurry thickening were analyzed by virtue of thickening and rheological experiments,and the thickening mechanism of hollow-microsphere containing this low-density cement slurry was discussed.Results show that,(1)the main reasons for thickening the hollow-microsphere containing the low-density anti-channeling cement slurry during temperature and pressure increase include broken hollow-microsphere and low compressive strength.Many bubbles in the hollow-microsphere dissolve into the slurry,so as to increase its consistency;and(2)selecting the efficient defoamer,flow regulator,and high strength hollow-microsphere appropriately based on the thickening mechanism can slow down the increase rate of consistency in the initial stage,so as to ensure safety.