Chemical–microwave–ultrasonic compound conditioning treatment of highly-emulsified oily sludge in gas fields

Abstract

The highly-emulsified oily sludge in gas fields is complex in components and serious in emulsification, which makes effective reduction extremely difficult only by a single direct mechanical separation method such as microwave heating, ultrasonic treatment, chemical conditioning, etc. In view of this, this paper presented a new chemical–physical compounding conditioning technology for such highly emulsified oily sludge in gas fields. The experimental samples, from the Mizhi Natural Gas Processing Plant of PetroChina Changqing Oilfield Company, were treated through chemical conditioning, from which the optimal formula, dosages and dosing order were determined. On this basis, the compound technology of chemical–physical conditioning was applied to reduce the specific resistance to filtration (SRF) of the sludge, thus achieving a satisfactory result. The following results were obtained. (1) The chemical conditioning agent with the formula of the oxidant MN-S, calcium oxide and sodium hydroxide was proved to achieve the fastest dewatering speed, and the specific resistance of sludge can be reduced from 130.3 to 3.81 trillion m3 per kg. (2) Comparison between microwave and ultrasonic conditioning methods shows that the latter is better in reducing the SRF (the ultrasonic frequency of 40 kHz was applied to reduce the SRF down to 14.01 trillion m3 per kg after 4 min of conditioning treatment). (3) The ultrasonic treatment effect after chemical conditioning is the best; the SRF was reduced to 2.77 trillion m3 per kg, and the moisture content of the sludge after mechanical dewatering was only 68.71%, decreased by 21.46% compared with the original content of 90.17%. In conclusion, this presented chemical–microwave–ultrasonic compound conditioning technology can reduce the sludge's SRF and the moisture content of filter cakes so as to achieve effective reduction of the highly-emulsified sludge in gas fields.