胶凝过渡态水泥浆防气窜能力评价方法

Method of Evaluating the Capacity of Gas Channeling Prevention of a Cement Slurry in Gelling Transition-State

环空气窜是多年来困扰固井工程界的技术难题之一。以水泥浆失重理论为基础,通过分析水泥浆有效液柱压力、内部结构阻力和地层流体压力三者间关系以确定验窜时机,结合连续采集水泥浆孔隙压力变化来判别气体是否克服水泥浆内部结构阻力而发生气窜,形成了一种可以直观考察处于胶凝过渡态水泥浆的防气窜能力评价新方法,以此方法研究了不同类型水泥浆的窜流情况,结果表明:①水泥净浆几乎无法抵抗气体侵入;②引入适量的降失水剂可轻微提高水泥浆基体的防气窜能力,但效果并不明显,仅能抵抗50 psi(0.344 MPa)的气窜压力;③防气窜水泥浆体系因防气窜剂的种类和加量变化,防气窜能力表现各异,通常能够抵御气窜压力范围为100~200 psi(0.689~1.379 MPa),部分防窜材料可以通过增大其加量达到提高防气窜能力的效果,但材料受自身特性影响,存在一定的气窜抵抗能力极限。该方法操作相对简便、实用性强、重复性较好,可横向对比评价不同类型防气窜水泥浆抵抗气体侵入的能力,为防气窜水泥浆体系设计优选提供有效参考。

Gas channeling in annular space is one of the technical difficulties encountered in oil/gas well cementing.Based on the theory of cement slurry weightlessness,the relationship among the effective fluid column pressure of the cement slurry,the internal structural resistance and the formation fluid pressure is analyzed to determine the timing of channeling detection.By continuously collecting data on the changes of the pore pressure in the cement slurry,it can be determined whether the gas has overcome the internal structural resistance of the cement slurry to cause gas channeling,and this leads to the invention of a new method for evaluating the anti-gas-channeling capacity of a cement slurry in transitional gelling state by direct observation.Using this method,the channeling of several cement slurries is studied.The study results show that:1)bare cement slurry is almost unable to resist gas channeling;2)by introducing appropriate amount of filter loss reducers,the anti-channeling capacity of a cement slurry can be slightly improved,with only limited effect;the cement slurry can only resist gas channeling pressure of 50 psi(0.344 MPa);3)changes in the type and concentration of the anti-gas-channeling agent lead to different anti-channeling capacity of a cement slurry.Generally speaking,cement slurries treated with different anti-channeling agents can stand channeling pressures in a range of 100–200 psi(0.689–1.379 MPa).Some anti-channeling agents exhibit higher capacities of anti-channeling by increasing their concentrations in the cement slurries,with limits of performance based on their inherent characteristics.The method described in this paper is easy and simple,and has good practicality and repeatability.It can be used to compare the performances of different antichanneling agents,and to provide reference to the design of anti-gas channeling cement slurries.