Research On High-Temperature-Resistant Foam Drilling Fluid For Geothermal Wells

High-temperature geothermal resources,as a clean energy,have great potential for development.Due to the low pressure coefficient,high temperature and prone to complex downhole accidents,high-temperature resistant foam drilling fluid has become the most promising type of drilling fluid for this type of formation.The preliminary experiments show that the anti-high temperature foam stabilizer is the key and focus of research and development of high-temperature resistant drilling fluid.This paper firstly conducts an in-depth investigation on the current status of high-temperature resistant foam drilling fluid technology at home and abroad and the geological characteristics of geothermal reservoirs and geothermal wells.Then the paper formulates the performance evaluation of high-temperature resistant foam drilling fluid for geothermal wells based on the existing evaluation methods of foaming agents for oil and gas wells.Finally,high-temperature resistant foam drilling fluids based on Janus particles and magnesium aluminum silicate were developed,respectively.Firstly,a series of Janus particles that differed in their hydrophilic lipophilic balance were facilely fabricated by the Pickering emulsion method.The relationship between the foam stabilization performance and the surface properties of the particles was systematically explored,and the foam stabilization mechanism was proposed.The results show that the(3-aminopropyl)triethoxysilane-SiO₂-dodecyltrimethoxysilane(NH₂-SiO₂-12C)Janus particles possess the best foam stability.Due to their suitable contact angle of80°,high positive?potential and good surface activity,these foams display the characteristics of a low surface tension,high dilational elasticity,non-spherical shapes,large sizes and thick films,which together result in the extension of the drainage half-life of the foam from 448 s to 778 s in comparison with the foam of pure foaming agent solutions.Moreover,NH₂-SiO₂-12C-stabilized foam can extend the drainage half-life to668 s after hot rolling for 16 h at 280°C and resist CaCl₂ concentration of 0.8 wt%.Therefore,Janus particles are expected to be promising candidates for use as foam stabilizers in high-temperature and high-calcium conditions.Secondly,nano-magnesium aluminum silicate(NMAS)and micro-magnesium aluminum silicate(MMAS)particles have been studied and compared with sodium bentonite(Na-Bent)as high-temperature-resistant foam stabilizers.NMAS even possesses excellent foam stabilization effect after being aged at 320°C for 16 h that it could still dramatically extend T_0.5 to 9.78 h,compared to 45.52 and 13.78 min for MMAS and Na-Bent,respectively.Furthermore,the initial foam volume(V₀)of Na-Bent-stabilized foam cannot resist the influence of NaCl and CaCl₂even when only 1.0 wt%NaCl or 0.1 wt%CaCl₂ is added.By comparison,V₀ of NMAS-and MMAS-stabilized foam drilling fluids are comparatively insensitive to NaCl and CaCl₂until the concentration of 3.0 wt%and 0.2 wt%,respectively.Through mechanism analysis,it is found that increasing the temperature could facilitate aggregation of clay dispersion,and the increase of particle size results in significant positive effect on apparent viscosity,interface dilational modulus,foam film thickness,and eventually drainage half-life(T_0.5)of the foam.Therefore,NMAS is an outstanding high-temperature-resistant foam stabilizer.In this study,particle-type high-temperature anti-foam foam stabilizers were prepared,and the influence of factors such as particle shape,size and surface properties on the stability of high-temperature and high-calcium foam was thoroughly studied.The study provides a solid foundation for high-temperature resistant foam drilling fluid research and a strong guarantee for the safe and efficient development of high-temperature geothermal resources.