硅酸钠前置液在委内瑞拉重油带固井中的应用

委内瑞拉重油带地区,稠油储藏深度浅,泥页岩盖层疏松,地层裂缝发育,以往固井作业采用常规前置液体系,井漏时有发生,固井环空冲洗净化能力差,界面胶结强度低,导致热采作业环空窜流及含H2S和CO2等地层酸性流体对漏封套管腐蚀,缩短了油井使用寿命。进行了硅酸钠溶液与泥岩地层中的CaCl2、MgCl2等盐类化合物成分反应生成硅酸盐类凝胶物质的实验,通过研究,将25%硅酸钠溶液应用于前置液,在冲洗液和隔离液之间注入,较好地解决了固井漏失问题,提高了封固质量和水泥界面胶结强度。指出,施工时硅酸钠溶液必须与水泥浆进行有效隔离,避免水泥浆污染增稠或稠化时间缩短。

Application of Sodium Silicate Prepad Fluid in Cementing Heavy Oil Zones in Venezuela

Viscous oil in the heavy oil zones in Venezuela is buried in shallow depths and the shale caps are unconsolidated.The reservoir formations have low pressure bearing capacity and are full of fractures.Conventional prepad fluids used in previous cementing jobs often resulted in lost circulations, making it difficult for the cement slurries to return to the designed depth.Cleaning of the annular spacing were generally poor during cementing, and cementation of the two interfaces(interface between casing string and cement sheath and the interface between cement sheath and borehole wall) is weak, resulting in annular channeling in thermal recovery and corrosion of uncemented casing string by acid gases such as H2S and CO2.The life of the production well is thus shortened.In field practices, it was found that by adding 25%sodium silicate solution into prepad fluid, lost circulation and discontinuity of cementing were prevented from occurring, the cement slurries in the annular space returned to the designed depth and the cement sheath was intact.Bond strengths of the two interfaces were enhanced.All these contributed to the prevention of casing damage by acid corrosion.The key point in cementing with sodium silicate prepad fluid is to prevent the sodium silicate from contacting with cement slurry, because the contact of the two will inevitably shorten the thickening time of the cement slurry and lead to cementing disasters.