Preparation And Properties Of Degradable Rubber Materials For Fracturing Tools

With the in-depth development of oil and gas resources,unconventional oil and gas resources show great potential.In recent years,70% of China's proven oil and gas reserves are unconventional oil and gas resources.Therefore,the development of unconventional oil and gas resources plays a great influence on the increase of oil and gas resource productivity in China.Staged fracturing in horizontal wells is the main technical measure to improve the production of unconventional oil and gas.At present,in the main promotion of staged fracturing technology,after the completion of the fracturing operations,the steps of drilling,grinding and milling are needed to remove the rubber packer,which are complex and takes a long time and affect the production efficiency of the fracturing operation much.In recent years,related fields domestic and abroad have attracted a great deal of attentions to develop degradable rubber sealing materials to realize the intervention-free operation of completion tools.Therefore,the development of high-performance degradable rubber sealing materials is of particular significance in the field of oil production engineering.Focus on the blank of domestic research of degradable rubber materials used in fracturing tools.The paper used millable polyurethane rubber(MPU),which degrades rapidly,as a matrix.The modification of polyether based double bond terminated polyurethane prepolymer(DTPUP),polyester based DTPUP,castor oil based DTPUP and hydrogenated nitrile butadiene rubber(HNBR)on MPU were studied.A series of degradable rubber materials were prepared and the properties of degradable rubber materials were studied.The dissertation consists of the following four parts:In the first part,polyether based DTPUP was used to modify MPU to fabricate polyether based DTPUP/MPU degradable rubber composites.The effects of the content of polyether based DTPUP on the mechanical properties,degradation behavior and thermal stability of the composites were studied.The results showed that in the mixed system,the tensile strength of the composites increases at first and then decreases with an increase of polyether based DTPUP in content;the degradation rate of the composites decreases with the increase of polyether-based DTPUP in content,and the degradation rate was the slowest when the polyether based DTPUP content was the highest.With an increase of polyether based DTPUP in content,the thermal stability of the material was improved.In the second part,polyester based DTPUP was used to modify MPU to fabricate polyester based DTPUP/MPU degradable rubber composites.The effects of the content of polyester based DTPUP on the mechanical properties,degradation behavior and thermal stability of the composites were studied,respectively.The results showed that in the mixed system,the content of polyester based DTPUP has little effect on the mechanical properties of the composites,however,the network structure constructed by vulcanization and cross-linking of polyester based DTPUP increases the retention of mechanical properties at higher temperature,and the degradation rate of the composites decreases with the increase of polyester based DTPUP in content,when the content was 50 phr,the mechanical property retention reached the highest value after immersion for 168 h.With an increase of polyester based DTPUP in content,the thermal stability of the material was improved.In the third part,castor oil based DTPUP was used to modify MPU to fabricate castor oil based DTPUP/MPU degradable rubber composites.The effects of the content of castor oil based DTPUP on the mechanical properties,degradation behavior and thermal stability of the composites were studied.The results showed that in the mixed system,with the increase of castor oil based DTPUP in content,the tensile strength of the composites increased at first and then decreased,the tear strength,modulus at 100% and hardness increased gradually,and the elongation at break decreased gradually;the degradation rate of the composites decreased with the increase of castor oil based DTPUP in content,and the retention of mechanical properties of the composites was the highest after immersion in water for 168 h when the content was30 phr.The initial decomposition temperature,the fastest decomposition rate temperature of hard segment and soft segment,and the thermal stability of the composites increased with the increase of castor oil based DTPUP in content.In the final part,HNBR was used to modify MPU to fabricate HNBR/MPU degradable rubber composites.The effects of blending ratio on vulcanization characteristics,mechanical properties,compatibility,thermal stability and degradation behavior of the composites were studied.The results showed that with an increase of HNBR in content the cross-linking degree of the composites decreases gradually,and the mechanical properties of the composites decrease slightly,the composites with any proportion exhibited good compatibility,and the thermal stability increases with the increase of the content of HNBR.The presence of HNBR greatly reduced the degradation rate of MPU.When the content of HNBR changed from 20 phr to 40 phr,the tensile strength retention of the composites increased from 27.0% to 52.1%,meanwhile the high tensile strength could be maintained between 48 h and 168 h to meet the sealing requirements.