不同含水情况下的泥岩蠕变试验及其对油田套损 影响研究

 以大庆泥岩为研究对象，进行不同含水条件下的强度试验和蠕变试验，分析含水量变化对泥岩强度、弹性模量等基本力学参数以及蠕变特性的影响。试验结果表明：含水量的增加，大大降低了泥岩的弹性模量和单轴抗压强度，并使泥岩的蠕变变形和稳态蠕变率显著增加。通过试验得到考虑含水量变化的泥岩蠕变本构方程，并与试验曲线进行对比。以大庆油田南二区某井套损段泥岩层为例，建立数学模型，根据得到的蠕变本构方程，对不同含水条件下井壁泥岩的蠕变挤压应力进行数值模拟，通过对比分析，说明在非均匀挤压应力作用下，泥岩含水量的增加会大大加快蠕变应力的增长速度，使围岩对套管产生的蠕变挤压应力达到极值所需的时间迅速减小，大大缩短套管使用寿命。油田开采过程中，应防止高压注入水进入泥岩，以预防和减少由于泥岩进水发生蠕变导致套管损坏。

EXPERIMENTAL STUDY ON MUDSTONE'S CREEP BEHAVIOR UNDER DIFFERENT WATER CONTENTS AND ITS EFFECT ON CASING DAMAGE

Strength and creep experiments of mudstone from Daqing Oil Field under different saturated conditions are performed through the XTR01 servo-controlled compression machine. The creep characteristics and the change of mechanical parameters with the increment of water content are analyzed. The results indicate that the rock strength and elastic modulus decrease with the increment of water content，while the creep strain and steady state creep strain rate increase. Through the experiments，the nonlinear creeping constitutive equation of mudstone considering the change of water content is established as compared with the creep characteristic curves. In water injection reservoir，based on the relationship between the water cut in the mudstone and the mechanical property of the mudstone，the mechanism of casing failure is analyzed，and the casing-cement sheath-mudstone creeping model is built in order to simulate the creep pressure of mudstone with different water contents. The simulation results show that under heterogeneous stress，the increasing water content accelerates the incremental rate of the creep pressure of mudstone，so the time of reaching yield state reduces significantly，which means service time of case becomes much shorter. During the process of water injection production，high injection pressure cut in mudstone should be prevented to reduce casing damage.