Study On Scaling Mechanism And Scale Inhibition Technic Of Weak Base ASP Flooding In Jing 11 Area Huabei Oilfield

Stratum and equipment scaling is one of the major problems encountered in the oilfield waterflood recovery process,especially in weak base ASP flooding technology of Jing 11 area Huabei oilfield.In this work,we will adopt the theoretical predictions and static experiment and computer simulation method to research the scaling mechanism and its inhibition technology.We predicted scaling tendency of formation water and injected water of Jing11 area by saturation index and stability index prediction methods according to the water ion content analysis.The result shows that both water sample have serious scaling tendency of calcium carbonate and no scaling tendency of calcium sulfate.The scaling tendency increased with temperature and Na₂CO₃ concentration.In order to verify the correctness of the theoretical predictions and ascertain the scaling laws and scaling mechanism,static scale experiment has been adopted.The result shows that the scaling rate increased with the increase of temperature,p H and concentration of calcium iron and Na₂CO₃.XRD analysis indicated that the component of the scale is calcium carbonate.The scaling mechanism of Jing 11 water sample is the changes of thermodynamic conditions,which would change the solubility of salt.We selected and evaluated the scale inhibitor against calcium carbonate which has been confirmed to be the major component of the scale.Static anti-scaling experiment was conducted to study the inhibition rate and its influencing factor of PASP,PAA,DTPMP and HEDP in actual working condition.Experiment result shows that the inhibition rate of four inhibitors followed the order:HEDP > DTPMP > PAA > PASP.The inhibition rate is more than 95% when HEDP concentration is greater than 2 mg/L and the inhibition rate sharply declined when the temperature reach 90?.In addition,the decrease of calcium iron and Na₂CO₃ concentration gives rise to the decrease of the HEDP inhibition rate.In order to meet the scale inhibition requirements of weak base ASP flooding,we find out that,scale inhibition rate of HEDP in water sample contained 20 g/L sodium carbonate can satisfy the requirements when HEDP concentration is more than 20 mg/L.In the end,we studied the interaction between the inhibitors and calcium carbonate crystal used the molecule dynamic calculations to explain the scale inhibition mechanism.We calculated the binding energy,deformation energy and the radial distribution function?RDF?of the carbonyl oxygen atoms in inhibitor with calcium ions in calcite crystal between four inhibitors and surface?104?and?1???0?.The simulation result shows that binding energy of four inhibitors followed the same order as inhibition rate gotten from experiment:HEDP > DTPMP > PAA > PASP,which declared that the interaction between inhibitors and calcium carbonate has great influence on scale inhibition.The deformation energy of four inhibitors is less than their binding energy,so the inhibitor molecule can be deformed by the adsorption of calcium carbonate crystal and attached closely on the crystal surface.The RDF analysis indicate that the inhibition mechanism of HEDP and DTPMP is the chelation between hydroxyl oxygen and calcium ion and the inhibition mechanism of PASP and PAA is the electrostatic interactions between carbonyl oxygen and calcium ion.