Research On Self-Select-Healing Material For Oil Well Cement

Oil well cement stone is a brittle material,which is easy to form microcracks inside.It generates a channel for formation fluid and affects the safe,efficient and green producing of oil and gas.Self-healing cement is an effective way to solve this problem.At present,oil expandable self-healing cement(SHC)has been used to stop oil channeling between oil lays,while water expandable self-healing cement has been used to prevent water channeling between water layers or marine shallow section.However,in many complex oil wells,it is difficult to cement the exact depth of the oil and water layers,especially thin interbedding of water and oil layers.The current SHC cannot solve fluid channeling between such layers.Therefore,it is necessary to achieve self-select-healing cement that can be triggered by whether water or oil.First,the Pickering suspension polymerization method was developed,and an oil absorbent material was prepared by using n-butyl methacrylate(BMA).The preparation process was stable and the oil phase was well dispersed without coalescence.The material had uniform particle size,good hydrophilicity,and has a core-shell structure.The oil absorption rate can reach 13.6,and the decomposition temperature was 220°C.The material had good compatibility with the oil well cement slurry,and can be used as the oil swellable component for the preparation of the self-select-healing materials.A super absorbent material was synthesized in an acidic environment of acetic acid by using dimethylaminoethyl methacrylate(DMAEMA)and acryloyloxyethyltrimethyl ammonium chloride(DAC).The most important property of the material was pH sensitivity.It absorbed much water in a neutral or weakly alkaline solution,but little water in a strong alkaline solution.The pH sensitivity mechanism of the material was analyzed.It is believed that the molecular chain of the material is affected by the pH value of the solution to stretch or collapse,thereby increasing or decreasing the water absorption rate.In addition,the water absorption properties of the material were greatly affected by the calcium ion concentration and were suitable for formations with a concentration of less than 0.05 mol/L.Thermogravimetric analysis indicated that the decomposition temperature of the material was 230°C.The cement slurry filtrate could reduce the water absorption rate of the material in water by the hydrolysis of OH^-and the crosslinking of Ca²⁺.However,the water absorption rate after reduction was still greater than the water absorption ratio in the cement slurry.The prepared pH-sensitive super absorbent material can be used as the water swellable component for preparing the self-select-healing material.Based on the developed oil swellable component and water swellable component,the microstructure of the water and oil dual-absorption material was designed.A microemulsion copolymerization method was developed,and the water and oil dual-absorption material was successfully prepared.The stability and structure of the microemulsion were analyzed by pseudo-ternary phase diagram and conductivity.DMAEMA is surface active and can help stabilize the microemulsion.The liquid absorption properties of the material were tested.It was found that the water phase monomer and oil phase monomer ratio was the main factors affecting the liquid absorption properties.The microstructure of the material could affect the water absorption properties of the material.The material was also pH sensitive.The cement slurry filtrate reduced the water absorption rate and oil absorption rate of the material by the hydrolysis of OH^-and the crosslinking of Ca²⁺.However,the water absorption rate after reduction was still greater than the water absorption ratio in the cement slurry.When the material addition was less than 10%of the cement,the cement slurry properties met the cementing operation requirements.The self-healing evaluation method and self-healing mathematical model for cement stone microcracks were established.The self-select-healing performance of cement stone added with the material was evaluated.When the amount of the material exceeded the critical filling factor of 0.490,the self-select-healing of cement microcracks could be realized.The development of water and oil dual-absorption self-select-healing material solves the problem of the application of self-healing material in oil well cement slurry due to single excitation conditions,and is of great significance for achieving long-term effective sealing of oil well cement sheath.