Properties of Sludge Produced from Offshore Oilfields and Its Harmless Treatment——an Example from SZ36-1 Oilfield

Compared with onshore oilfields, offshore oilfields are characterized by high permeability of reservoir, serious heterogeneity, low rock cementation, high viscosity of crude oil, and low recovery efficiency by water flooding. In addition, offshore oilfields are high in operation cost and short in service life of the platform. Therefore, it is necessary to accelerate development rate in early stage of polymer injection flooding. But due to the polymer injection, the formation pressure increased greatly, resulting in further damage in rock texture, and the mud content in produced liquid increased greatly. The work efficiency of oil-water separation system decreased due to high mud content in produced liquid. Therefore, it is urgent to treat harmlessly the sludge produced from offshore oilfields. Based on reservoir engineering, polymer materials and physical chemistry, study on reservoir properties, sludge composition and its reservoir adaptability have been conducted by instrumental testing, chemical analysis and physical simulation, profile control effect of sludge polymer solution .The results show that withdrawn sludge is composed of water, clay particles and oil. The soil particles are not of uniform size and regular appearance, composed mainly of oxygen, carbon, silicon. When the polymer concentration ranges from 0.06% to 0.3%, and mud concentration is less than 0.6%, the sludge polymer solution can meet the technical requirements of pumping and plugging large channels of reservoir. Reinjection of withdrawn sludge into formation is an effective way of harmless treatment of sludge, low in operation cost, high efficiency in plugging compared with the traditional polymer gel and particle profile control agents.