Polymer/Silica Nanocomposite As Functional Oilwell Cement Additives For Deep/Ultradeep Oil And Gas Wells Cementing

Nowadays,oil and gas resources are still the mainstay of energy consumption.As the exploration and development of oil and gas is extending into the fields of deep layers,low-pressure,-permeability,-abundance,offshore and non-conventional reservoirs,well cementing becomes more and more difficult.High or ultrahigh temperature cementing is a technological problem for deep and ultradeep wells,which demands a mutifunctional cement slurry and cementing materials.At present,the domestic polymer retarder generally exhibits poor retarding effect,strong dispersion and slows the strength development of hardened cement down at large temperature difference.Moreover,polycarboxylic additives occassionally cause the abnormal gelation of cement slurry.For polymer fluid loss additive,it shows some disadvantages including inferior high-temperature and salt tolerance,strong dilution and so on.In this dissertation,polymer/silica nanocomposites have been designed and synthesized via the nano-modification technology,used as high temperature retarder and fluid loss additive,respectively.The abnormal gelation of cement slurry containing polycarboxylic additives was studied and some corresponding solutions were put forward.A polymer/silica nano-composite ADNIOS as a high temperature retarder was synthesized using 2-acryli-amide-2-methylpropane sulfonic acid(AMPS),N,N-dimethylacrylamide(NNDMA),dimethyl diallylammonium chloride,itaconic,octadecyl dimethyl allylammonium chloride(ODAAC)and nanosilica modified by triethoxyvinylsilane(VN).Its microstructures were characterized,showing that ADNIOS is the anticipated product and has good thermal stability and remarkable molecular structure.Its applied properties were also performed.The results indicate that it has the advantages of wide applicable temperature range from 90 ~oC to 210 ~oC,effective retarding and slight dispersion effect at high temperature.The thickening time of cement slurry is insensitive to the slight variation of test temperature and polymer addition.Moreover,the compressive strength of set cement embracing ADNIOS develops normally at a large temperature difference.The retarding mechanism and adsorption kinetics of ADNIOS were also studied,and the hydration kinetics of ADNIOS modified cement was performed by microcalorimetry.A high temperature fluid loss additive HAPSF was developped via the copolymerization of AMPS,NNDMA,maleicanhydride(MAH),ODAAC and VN.Its structures were characterized by some effective techniques.The results show that HAPSF shows excellent high-temperature tolerance,salt-,shear-resistance as well as viscosifying effect.The applied performance demonstrates that the API fluid loss of cement slurry with HAPSF can be less than 70 mL at 240 ~oC.Moreover,it can be applicable for a wide temperature range from 30 ~oC to 240 ~oC and saturated brine slurry.Meanwhile,it exhibits slight dilution under high temperature and is in favor of the compressive strength development of set cement.The enhancement and fluid loss control mechanisms of HAPSF were studied,showing that it can improve the compactness of set cement and promote the formation of cement hydration products through its pozzolanic effect,inducing the rapid mechanical strength development of set cement.Additionally,the fluid loss control of HAPSF can be achieved through the plugging effect,adsorption and improvement of cement filter cake quality.The comprehensive performance of low-,normal-and high-density cement slurry with ADNIOS and HAPSF was performed.The results indicate that the designed cement slurry can be applied at 210 ~oC(BHCT),and its good comprehensive properties can meet the requirements of oil and gas oil well cementing.Hence,both of them have great potential application in deep,ultradeep wells,high temperature and high pressure gas wells cementing as well as long cementing interval.