Study On The Stabilization Mechanism And Oil/Water Separation Chemicals Of Polymer Flooding Produced Oily Water

Polymer flooding has been widely adopted in Daqing Oilfield to enhanced oil recovery. In 2001, 8 million metric ton crude oil was produced by polymer flooding. With the application of polymer flooding, the stability of the inverse oil/water emulsion in produced oily water of Daqing Oilfield has been significantly increased. The tight oil/water emulsion in polymer flooding produced oily water has significantly reduced the treating ability of some old oily water treating facilities. What is worse is that the treated oily water from some oily water treating facilities is seriously out of specification. The reaction between the residual anionic polyacrylamide in the produced oily water and the state-of-the-art cationic flocculant and coagulant has lead to significant increase of flocculant/coagulant dosage, plugging of oily water filters and worse quality of the treated oily water.Stabilization of inverse crude oil emulsion in polymer flooding produced oily water of Daqing oilfield was investigated through water quality analysis, interfacial active particle separation and tests on oil-water separation of both artificial and genuine polymer flooding produced oily water. The enhanced stability of inverse crude oil emulsion in polymer flooding produced oily water primarily results from adsorption of colloidal particles on oil droplets which presents steric hindrance to oil droplet coalescence and decreases the density difference between the oil droplet and the water phase. Residual polymer in polymer flooding produced oily water enhances its stability by promoting deposition of colloidal particles on oil droplet surface and increasing water phase viscosity, leading to lower oil droplet floating velocity. An oil/water separation agent, formulated mainly with nonionic and anionic active components, was developed for polymer flooding produced liquid and oily water. The newly developed oil/water separation agent works well both as demulsifier for o/w type polymer flooding produced crude oil emulsion and as flotation agent for polymer flooding produced oily water. With the dosage of the newly formulated oil/waterseparation agent at 20mg/L, polymer flooding produced liquid can undergo well phase separation after Ih 45C thermal settling, resulting in only 2.88% water in the oil phase and 651.1 mg/L oil in the water phase. With the dosage of the newly formulated oil/water separation agent at 20mg/L, the oil content of polymer flooding produced oily water can be lowered from 827mg/L to 23.9mg/L after 6min induced air flotation. Based on the performance of the newly developed oil/water separation agent, a thermo-chemical settling - flocculation process, in which the newly developed oil/water separation agent is injected inte polymer flooding produced liquid upstream of free water knock-out, was proposed for the oil/water separation of polymer flooding produced liquid and oily water.