Study On Modification Method And Evaluation Of Cement For Deep Shale Gas Well Cementation

With the continuous exploitation and consumption of shale gas in the middle and shallow layers,in order to achieve stable and sustained growth of shale gas reserves for a long time,the breakthrough in exploration and development of deep shale gas is the key.Deep shale gas is very rich in resources,has huge potential,and has a low degree of development.It is a key research field in the future.The deep shale gas has a large vertical sag and high formation fracture stress.After large-scale volume fracturing,it faces the problem of wellbore integrity failure.Although the elastic modulus of ordinary elasticity and toughness cement slurry is low,the strength is also relatively low,which can no longer satisfy the seal integrity under higher fracturing load.Therefore,from the perspective of the principle of toughening,this paper selects a high-performance toughening agent,surface-modifies it,constructs a high temperature resistant high strength elastic toughness cement slurry,and evaluates the integrity of the cement ring seal to solve the deep page Rock gas well cement ring seal failure problem.The specific research work is as follows:(1)Study on toughening mechanism and optimization of toughening materialsFirstly,the instability model of cement sheath in deep shale gas horizontal well under the high stress and fracturing conditions is systematically analyzed,and the idea of research and development of cement slurry system is put forward;the mechanism of elastic toughening is studied,the principle of optimization of toughening materials is formulated,and the elastic particles with the best elastic modulus reduction are selected as toughening materials,and the surface modification is carried out to optimize its dispersion performance.Based on the close packing theory of powder materials and the crystal transformation of cement hydration products,nano-Si O₂ particles were selected and surface modified to fill the pores produced by cement hydration.The calcium sulfate whisker material with large slenderness ratio was selected to increase the tensile strength of the cement stone,and it was in powder form to facilitate the ash mixing uniformity.(2)Construction and performance study of high-strength elastic-toughness cement slurry systemExperiments were carried out on the blending amount of various materials,and their respective optimal blending amounts were obtained,and compounding experiments were carried out to establish the optimal blending ratio of the cement slurry system.The performance of the cement slurry was evaluated,and it was concluded that the performance of the cement slurry could meet the basic requirements of on-site construction.By evaluating the mechanical properties of the modified cement stone,the weak point of the ordinary elastic toughness cement stone is significantly improved,and a high strength elastic toughness cement stone with high tensile and compressive strength and low elastic modulus is formed.(3)Study on microscopic mechanism of modified particlesThe phase composition of the modified cement stone was analyzed by X-ray diffraction method.The microscopic morphology of the cement stone hydration product and internal strengthening materials were observed by electron scanning microscope.At the same time,the pore parameters of the modified cement stone were tested and compared.The elastic particles improve the brittleness of the cement stone;the modified nano-Si O₂ particles are plasticized by filling the pores and crystals to enhance the deformability and compressive strength of the cement stone;the long and thin whiskers act as bridges in the cement stone The chain action hinders the development of cracks and increases the tensile strength.(4)Evaluation of cement ring seal integrityThe sealing performance of the modified elastic-toughness cement stone under simulated conditions was evaluated by an evaluation device.The results show that the modified elastic-toughness cement stone can meet the sealing integrity under a 120 MPa fracturing load,and can complete the complete shale gas well to the cement ring Sexual requirements.