Experimental Studies On Oilfield Scale Control And Removal By Acoustic Treatment

The oil field production is greatly affected by scaling in wellbores, reservoirs and surface equipments. Effective measures for scale control and removal must be taken. Acoustic treatment is a new physical technique for scale control and removal. However, the mechanisms for acoustic treatment are so shallow that they should be studied further.The effect of acoustic wave on scale dissolution was conducted by ion titration method and a new approach for the evaluation of antiscaling effectiveness of calcium sulphate scale under laboratory static conditions was designed. By orthogonal experiments, a series of experiments were carried out to study the influencing factors of acoustic treatment for scale control and removal and parametric optimal design was accomplished. The effect of acoustic treatment on the process of scaling on microscopic view was observed using a microscope.Experiments show that scales can be dissolved by acoustic treatment. The rate of scale control for calcium sulphate scale increases with the increase of acoustic power, acoustic irradiation time and temperature and the rate of scale control can reach 93.73%. Factors affecting acoustic antiscaling effectiveness of calcium sulphate scale from major to minor are pH value, temperature, mixing concentration, acoustic irradiation time and acoustic power. For calcium carbonate scale, acoustic antiscaling rate which can reach more than 90%, increases with acoustic irradiation time and is also affected by temperature to some extent. The crystal size decreases by retarding initial time of acoustic irradiation through photos observing and comparing. With increase of temperature and supersaturation, crystal size becomes tinier and crystals distribute more glomerately. Acoustic wave builds different types of crack on crystals, which makes it much easier to be broken into tinier pieces. The mechanisms of scale control and removal by acoustic treatment can be concluded as follows: (1) The scale can be dissolved by acoustic treatment to increase its solubility, which inhibits the precipitation of scale crystals; (2) The action of acoustic cavitation can break the scale crystals into small pieces to prevent them from growing up and disperse the scale crystals to prevent them from agglomerating. (3) The mechanical shearing effect of acoustic wave can make the pipe walls clean to prevent scales depositing on pipe walls. Therefore, acoustic wave can control and remove scale during all three steps of scaling.