盐岩蠕变对固井质量的影响

盐岩具有较好的可塑性,在钻井及固井过程中易发生塑性变形或蠕动流动,经常造成盐岩层段固井水泥胶结较差。为给盐层段固井质量评价提供理论依据与指导,通过盐岩力学及蠕变实验获取了盐岩力学特征及蠕变特性参数,构建了盐岩蠕变模型,分析了研究区的实际工程资料。结果表明：相同应变条件下,围压越大,盐岩承载能力越强,弹性模量越大；不同围压条件下,盐岩表现为典型弹塑性变形特征,盐岩破坏类型为扩容破坏；偏应力越大,瞬时弹性应变越大,稳定蠕变应变率越大；随着盐岩的蠕变,固井二界面密封能力在短时间内迅速增大,1000h后增速变缓并以一较小的稳定速度继续增大,且工程实践与数值模拟结果得到相互验证。可见评价模型与方法对盐岩层段固井质量评价具有积极实践意义,亦可对其他地区类似地层提供有意义的借鉴。

Effects of Salt Rock Creep on Quality of Well Cementing

Salt rock has good plasticity and is prone to plastic deformation or creep flow in the process of drilling and cementing, which often leads to poor cementing of salt rock section. In order to provide theoretical basis and guidance for cementing quality evaluation of salt interval, the mechanical characteristics and creep characteristic parameters of salt rock were obtained through salt rock mechanics and creep experiments, the creep model of salt rock was constructed, and the actual engineering data of the study area were analyzed. The results show that: under the same strain condition, the greater the confining pressure is, the stronger the bearing capacity of salt rock is, and the greater the elastic modulus is; under different confining pressure conditions, salt rock shows typical elastic-plastic deformation characteristics, and the failure type of salt rock is dilatancy failure; the greater the deviatoric stress is, the greater the instantaneous elastic strain is, and the greater the steady creep strain rate is; with the creep of salt rock, the sealing capacity of cementing interface is reduced in a short time It increases rapidly, slows down after 1000 hours, and continues to increase at a small steady speed. The engineering practice and numerical simulation results are verified each other. It can be seen that the evaluation model and method have positive practical significance for cementing quality evaluation of salt rock section, and can also provide meaningful reference for similar formations in other areas.