盐膏层固井用降失水剂的研究与应用

Study and Application of Fluid Loss Additive Used in Cement Slurries for Cementing Salt-Gypsum Stratum

针对塔里木油田库车山前高压天然气井盐膏层溢漏同存、安全密度窗口窄等固井难题,通过优选功能性单体,合成了具有耐温抗盐且分散性好等特性的降失水剂FL-A。红外光谱分析结果表明,单体均参与了聚合反应;热重分析结果表明,FL-A具有良好的耐热性能,耐温达300℃;水泥浆性能评价表明,该降失水剂控失水性能好,抗盐达饱和,与其他外加剂配伍性好,稠化线型正常。采用该降失水剂配制的密度为2.3~2.6 g/cm^(3)含盐高密度水泥浆体系在105~180℃高温下具有液固比低、失水量小、沉降稳定性好、流变性能优、强度发展快等特性。在盐膏层固井应用10余井次,封固质量良好,高压盐水均得到有效封隔。

High pressure natural gas well cementing in the piedmont structure in Kuche, Tarim Basin has encountered problems such as coexistence of well kick and mud losses in the salt-gypsum stratum, and narrow safe drilling windows etc. To deal with these problems, some functional monomers were selected and used to produce a fluid loss additive FL-A with high temperature tolerance,salt resistance and good dispersibility. IR analysis showed that the monomers all took part in the polymerization reaction.Thermogravimetric analysis showed that FL-A has good thermal stability;it functions normally at 300 ℃. In laboratory evaluation,cement slurries treated with FL-A has good filtration control capacity, and can be used in salt-saturated cement slurries. FL-A has good compatibility with other additives and normal thickening curve. Several cement slurries, with their densities between 2.3 g/cm^(3)and 2.6 g/cm^(3), were formulated with saturated saltwater and treated with FL-A. These cement slurries have low liquid/solid ratios,low filtration rate, good settling stability, excellent rheology and fast-developing strengths. They have been used more than 10 times in cementing wells penetrating salt-gypsum stratum, the job quality was satisfactory and the high pressure formation saltwater was effectively isolated.