Research On CO 2 Pollution Mechanism And Treatment Technology Of Water-based Drilling Fluid

Water-based drilling fluid is the most commonly used drilling fluid system in China.When drilling in strata containing CO₂,CO₂ gas will invade into the drilling fluid.Which makes seriously affect on the performance of drilling fluid and drilling construction,such as deterioration in drilling fluid rheological property,filter loss out of control,causing heavy losses to the drilling operation.Aiming at these problems,the rationality of the sodium carbonate in simulating CO₂ pollution was demonstrated.The influence of HCO₃^-/CO₃^2-on the law of the clay slurry,including apparent viscosity,plastic viscosity,gel strength,yield point,filtration,zeta potential,clay particle size,etc was nvestigated at 50 ℃,90 ℃ and 150 ℃ respectively;And then we investigated the adsorbing capacity of SMP（including the SMP-I and SMP-II,SMP-III）on the clay when suffered CO₂ pollution;finally,the performance changes of polluted mud slurry by CO₂ before and after treatment was investigated,Which including apparent viscosity,plastic viscosity,gel strength,yield point,filtration,zeta potential,particle size,and adsorbing capacity of SMP on clay.Based on the above investigation,hypothesis of CO₂ pollution of drilling fluid was put forward:HCO₃^-/CO₃^2-makes the clay particles finely dispersed,and with the increase of the HCO₃^-/CO₃^2-concentration,the clay particles further flocculation,forming a spatial network structure,the drilling fluid viscosity and gel strength increase;At the same time,the competitive adsorption occurs between HCO₃^-/CO₃^2-and drilling fluid additive,it make additive adsorption on clay particle content decrease and result in treatment failure,and also lead to the hydration shell on the surface of clay particles thinning.Then fluid loss amount increased.The structural strength of polluted mud slurry was investigated by using rheometer,and the morphology of mud slurry was watched by SEM,all the result as well as on the clay surface water film analysis indicate that these assumptions are correct.According to the research results,puts forward the treatment of water-based drilling fluid CO₂ pollution.And based on this,a oil field experiment was conducted in two CO₂ contaminated wells:well MX46-X1 and well MX008-6-X2.After the treatment,drilling fluid viscosity,gel strength,rheology and filtration control,fully meet the needs of the project,to achieve the desired purpose.