一种评价水泥浆沉降稳定性的新方法——微压力波动测试水泥浆滤失—沉降耦合作用

目前的水泥浆沉降稳定性测试方法缺乏对沉降过程的描述。为了提高水泥浆沉降稳定性测试的准确性与科学性,设计了一种微压力波动测试仪,对滤失—沉降耦合作用的水泥浆柱分段压力波动进行测试,据此评价浆体的上、下密度差,并对不同黏度、温度、降失水剂、固相颗粒和触变性的水泥浆稳定性进行了分析。研究结果表明:①水泥浆沉降过程可分为高速期、低速期、稳定期和失重期,高速期滤失可减小浆体的上、下密度差;②滤失量越大、黏度越低、同类材料水固比越大,密度差越大、沉降稳定性越差;③温度对沉降稳定性的影响因降失水剂的协同作用而呈现出无规律性,高分子聚合物类降失水剂效果强于成膜类;④提高水泥浆触变性可改善浆体的沉降分层现象,胶凝强度的形成时间越短,效果越好。结论认为,较之于常规方法,该评价水泥浆沉降稳定性的新方法,可以对沉降全过程进行描述,并考虑了滤失对沉降的影响,更加贴合于井下的实际情况。

A new method for evaluating settlement stability of cement slurry: Micro-pressure fluctuation tests for cement slurry filtration–settlement coupling

The existing cement slurry settlement stability test methods cannot describe the process of settlement. To improve the accuracy and scientific nature of cement slurry settlement stability tests, we designed a micro-pressure fluctuation tester to test the pressure fluctuation at each segment of slurry column under the coupling condition of water loss and settlement. And based on this, we evaluated the upper-lower density difference of the slurry, and analyzed the stability of the cement slurry at different viscosities, temperatures, water losses, solid particles and thixotropy. And the following research results were obtained. First, the settlement process of cement slurry can be divided into high speed period, low speed period, stable period and weightlessness period, and the water loss in the high speed period can reduce the upper-lower density difference of the slurry. Second, the larger the water loss, the lower the viscosity. For the materials of the same type, the greater the water-solid ratio, the greater the density difference and the poorer the settlement stability. Third, the effect of temperature on the settlement stability is irregular due to the synergetic effect of water loss reducer. The effect of the water loss reducer of high molecular polymer type is stronger than that of film-forming type. Fourth, increasing the thixotropy of cement slurry can improve its settlement stratification. The shorter the formation time of bonding strength, the better the effect. In conclusion, compared with the conventional method for evaluating the settlement stability of cement slurry, this new method can describe the whole process of sedimentation and it takes the effect of water loss on settlement into consideration, so it can reflect the actual downhole situations more accurately.