Study On Inter-salt Shale's Creep Pattern And Mechanism Of Casing Deformation

Due to vast distribution range,abundant of oil content and high formation pressure of inter-salt shale,its development potential is significantly huge.However,the fact that mentioned formation contains complex interbedding,which includes not only salt formation with high creep potential,but also shale formation with salt crystals inside,makes it harder to maintain casing integrity.Unlike salt formation with high potential to creep,or shale formation with no creep-like behavior without the existence of water,inter-salt dolomitic shale shows a complex creeping potential regarding two factors: one is that due to water-injecting technique,creep is more complex with a dissolution cavity inside;the other is that water will change the mechanic behavior of shale,making it easier to creep.Research regarding salt of shale formation is rather complete,but rarely do researchers investigate creep behavior in interbedding formations.Based on the particularity of inter-salt shale,this paper completed 3 parts of work:(1)using indoor triaxial creep test,a creep model was selected regarding the moisture content of rock samples;(2)using ANSYS,casing load under formation creep was simulated;(3)based on current designing standard,casing strength of inter-salt shale was calculated,and project case was also solved using mentioned theory.Results from experiment and simulation showed that: Deionized water can accelerate inter-salt shale's creep rate,while formation water somehow reduces mentioned creep rate;if a cavity was formed during injection,casing failure is bound to happen;12.7 mm or thicker casing with a can reduce casing failure caused by inter-salt shale creep.