Feasibility Study On Returning Oil Sludge In Offshore Oilfield

In China, the annual output of oily sludge origined from process in the petroleum and petrochemical industry has exceeded one million tons, which seriously affected the on-site production conditions and the surrounding ecological environment. With the increasingly frequent activities in petroleum prospecting and exploitation, the output will steadily picking up, and the treatment of oily sludge become much more difficult. For SZ36-1oil fields, heavy oil reservoir properties, reasonable sanding technique and polymer flooding technology not only exacerbated sanding in the oil wells, but also increased the difficulty in disposal of oil sludge. Simultaneously, the limited production platform space is not suitable for large-scale processing equipment; sediment particles were too large to directly re-injected into the formation for profile control, with the problem of well and layer selection, and can not achieve continued processing of oily sludge. Therefore, harmless treatment and resource utilization of oily sludge in offshore oil field has been becoming a serious issue demanding prompt solution.Firstly, composition analysis, particle size distribution measurement of oily sludge from SZ36-1oil field land terminals were carried out, and found that is difficult to directly re-inject into formation for its big size. The flexible grinding unit of the skid-mounted polymer rapid dissolution device could reduce the size of solid particles to meet the requirements of re-injection. Particle size analyses of grinded oily sludge showed that the crude oil and other impurities in oily sludge resulted in adhesion and gather of solid particles, and formed a larger aggregate structure with easy sedimentation in aqueous solution. Therefore, the hydrophobic associating polymer AP-P4solution was applied to effective dispersion and suspension of solid particles, and developed effective oily sludge re-injection system. The injecting performance of the oily sludge re-injection system was correspondly researched according to the matching relationship of the sediment particle size and the formation pore throat size. The study confirmed the feasibility of re-injecting oily sludge and achieved its long-term injection for offshore fields.At the same time, it is also considered that the effct of grinded oily sludge on the properties of AP-P4solution (apparent viscosity, stability, rheology and visco-elasticity, etc.). In the oily sludge re-injection system with a certain amount of oily sludge, the AP-P4adsorbed on the surface of the particles and formed a network structure through the polymer molecules interaction, with particles suspended in the solution, thereby enhanced its solution properties; But excessive grinded oily sludge caused dramatical reduced performance in the polymer solution. In the process of re-injection, the solid particles or aggregate structure effectively blocked the high permeability zones of heterogeneous reservoir and resulted in reversal in injectivity profile, improved the producing degree of low permeability layers and enhanced the oil displacement efficiency of polymer flooding in non-homogeneous layer. But high levels of oily sludge in the system not only degrade the performance of polymer solution, but also speeded up the aggregation and sedimentation of sediment particle, restricting their deep migration and affecting the polymer flooding.The flexible grinding unit of the skid-mounted polymer rapid dissolution device could reduce the size of solid particles and developed effective oily sludge re-injection system with AP-P4solution, achieved long-term injection for SZ36-1oil field, and enhanced the oil displacement efficiency of polymer flooding in non-homogeneous layers, achieved effective water control and stabilized oil production. Simultaneously, developed a new way for the harmless disposal and resource utilization of oily sludge, and also provided a reliable technical support for oil field comprehensive treatment and reducing production costs, with strong promotional practical value.