Study On Borehole Wall Instability Mechanism Of Permian In Tahe Oil Field And Development Of Drilling Fluid With Strong Anti-collapse And Restraint

Yubei Block of Tahe oil field,located in the outskirts of Tarim Basin,is an important exploration and development block of Sinopec Group.Especially the Permian formation has low fracture pressure and low bearing capacity.Block loss is serious in the igneous section of Kupkuzman Formation and Kaipaizrek Formation.With the continuous exploration and development of Yubei block,the problem of borehole wall instability in Permian is more prominent,and it is urgent to solve the problem of borehole wall instability in Yubei block.In this paper,by studying the mechanism of borehole wall instability in Yubei block,a drilling fluid system with strong anti-collapse and restraint was developed and successfully applied in Yubei block.The main work is as follows:(1)Based on previous logging and drilling data,the lithological characteristics,safety density window,bearing capacity,collapse pressure and wellbore collapse cycle of different Permian formations in Yubei block are analyzed.The mineral composition and structural characteristics of different Permian strata were analyzed by X-ray diffraction and scanning electron microscopy.The physical and chemical properties of the rock are characterized by measuring the density,cation exchange capacity,expansion rate,recovery rate and specific water absorption of the drilled core.Based on the analysis of experimental data,the mechanism of borehole wall instability of Permian in Yubei block is obtained.(2)For deep wells,drilling fluids are required to have high temperature resistance.AM?AMPS and AA monomers are designed and synthesized.The synthesis conditions were optimized by adjusting the monomer ratio,initiator dosage and monomer dosage.The molecular structure of high temperature filtrate reducer was characterized by infrared spectroscopy,scanning electron microscopy and thermogravimetric analysis.The temperature resistance,calcium resistance and salt resistance of the synthesized filtrate loss were evaluated,and the mechanism of filtrate loss reduction was revealed.(3)The inhibition mechanism of chitosan ammonium salt(CAS)was studied.The experiments of linear expansion test,rolling recovery of shale,secondary rolling recovery and inhibiting bentonite pulping show that chitosan ammonium salt has excellent ability to inhibit shale hydration.Compared with potassium chloride and polyamine inhibitors,chitosan ammonium salt has better inhibition performance and sustained inhibition ability.(4)With the synthetic filtrate reducer as the core treatment agent,a strong anti-collapse and inhibition drilling fluid system has been formed.By optimizing the main components,such as shale inhibitor,film forming agent,polymer cementitious leak plugging agent PSD and rigid leak plugging agent while drilling,a strong anti-collapse and inhibition drilling fluid system has been formed.The temperature resistance,salt resistance,calcium resistance,aggravation performance,pollution resistance and inhibition performance were systematically evaluated.(5)The anti-collapse and strong inhibition drilling fluid system has been successfully applied in Yubei block.Field application shows that the optimized anti-collapse and strong inhibition drilling fluid system can effectively solve the problem of borehole wall instability in the Permian formation of Yubei.The research work in this paper can effectively solve the problem of Permian wellbore stability in Yubei block,and is expected to be popularized and applied in Yubei block.