Research On The Technology Of Ultra-high Temperature And Ultra-high Density Water Based Drilling Fluid

With the development of petroleum exploration and development technology in our country,the target reservoir formation had extended from the middle-shallow formation to the deep formation and the ultra-deep formation,and the technology of ultra-high temperature and ultra-high density（ultra-HTHD）water based drilling fluid has become one of the key technologies in drilling engineering.This paper mainly aimed at the technical problems of the rheology regulation and the stability control of ultra-high temperature and ultra-high density water based drilling fluid,and mainly focused on the mechanism of ultra-high temperature and ultra-high density water based drilling fluid.Explored and established the new theory and new method for ultra-high temperature and ultra-high density water based drilling fluid.With the development of polymeric filtrate reducers with high temperature resistance for anti-high temperature water base drilling fluid as the starting point,eventually optimized and development the ultra-high temperature and/or ultra-high density water base drilling fluid formulations which were suitable for deep and ultra-deep well drilling.During the HTHP drilling process,water as the continuous phase of the water-based drilling fluid is usually in the subcritical state.The dielectric constant,viscosity and the surface tension of water gradually decrease,the water ionization constant gradually increases,the hydrogen-bond interaction and the intensity of hydrogen-bond are obviously weakened and decreased with the increase of temperature,resulting in the subcritical water will become an extraction solvent,chemical reaction medium or acid and alkali catalyst.And also can lead to the occurrence of thermally induced phase separation that the lower polar molecules of solute gradually dissolve in water and the solubility of the strong polar molecules of solute solubility gradually becomes worse,even separates out from the solvent.It was found that the changes of the physical or chemical properties of water under the environment of high temperature and high pressure were not conducive to the efficacy of water-soluble drilling fluid additives,and even lead to lose its effectiveness.Based on the physical and chemical properties of subcritical water and its effect on the performance of ultra-high temperature ultra-high density water based drilling fluids and in order to make the polymer has better compatibility properties in subcritical water,a new idea and a new method for the molecular structure design of polymeric additives for ultra-high temperature water-based drilling fluids based on the physical and chemical properties of subcritical water was been proposed,and a new type of polymeric filtrate reducer with special molecular structure was designed.A Zwitterion hydrophobic associating polymeric filtrate reducer which was coded as SDT10 with high temperature resistance was synthesized by radical micelle copolymerization.The molecule structure,relative molecular weight,thermal stability,biological toxicity,etc.of SDT10 were analyzed using FT-IR analysis,¹H-NMR analysis,GPC experiment,TG analysis,combined with biological toxicity analysis,etc.And the mechanisms of filtration reduction and salt tolerance with high temperature resistance of SDT10 in water base drilling fluids were finally discussed.The results showed that the newly synthesized SDT10 had excellent properties of filtrate reduction with high temperature resistance,and with an especially significant property of compound salt tolerance.SDT10 had better properties of filtrate reduction even if it under the composite brine drilling fluids which the concentration of Cl^-1 was greater than 90000 ppm,concentration of Ca²⁺was greater than5000 ppm,concentration of Mg²⁺was greater than 15000 ppm and with low pH,and made the performance of SDT10 better than the other similar products at home or abroad.In order to promote the temperature resistance properties of polymers,based on the optimization design of molecular structure of the novel polymer,a hydrophobic associated polymer based nano-silica filtrate reducer with core-shell structure which was coded as SDT11 was synthesized using the matrix of block hydrophobic associated polymer and the filler of nano-silica.The molecule structure,micro-morphological features,and relative molecular weight of SDT11 were analyzed using FT-IR analysis,SEM analysis,TEM analysis,and combined with GPC experiment,etc.And the mechanism of filtration reduction of SDT11 in water base drilling fluids was finally discussed.The results showed that the newly synthesized the hydrophobic associated polymer based nano-silica filtrate reducer with core-shell structure also had excellent properties of filtrate reduction and property of high temperature resistance.And the filtrate reducer with hydrophobic associated polymer based inorganic nano-composite which had better properties could be obtained by introducing the nano-silica which was as a filler into the molecular chain of newly developed hydrophobic associated polymer.Because it could combine the properties of rigidity,dimensional stability and thermal stability of inorganic nano-silica with the properties of temperature resistance,salts resistance and anti-pollution performance of hydrophobic associated polymer.At the environment of high temperature and high pressure,the SDT11 molecule with special cross-linked structure had a good ability to protect and stabilize the colloidal stability of drilling fluids by maintaining the liquid viscosity of drilling fluid,and keeps the solid particle size distribution reasonably through chemical adsorption,hydration,and hydrophobic association.In this way,thin and compact mud cakes are formed,and thereby it can control the HTHP filter loss efficiently.On the basis of theoretical research and the study of indoor experiments,the two kinds of new methods and new ways of rheology regulation for ultra-high temperature and ultra-high density water-based drilling fluid were revealed.And established the new theory and new method for ultra-high temperature and ultra-high density water-based drilling fluid based on the Grain Accumulation Theory,and the new way which was guided by the Synergistical Increase Theory for optimizing the formulation of ultra-high temperature and ultra-high density water-based drilling fluid.Finally,using the newly synthesized SDT10 and SDT11 as the key drilling fluid additives,the ultra-high temperature water based drilling fluid formulation with anti-temperature up to 248℃and the ultra-high temperature and ultra-high density water based drilling fluid formulations with anti-temperature up to 220℃to 240℃were optimized respectively.