Partition coefficient difference of benzocarbazole isomers between oil, water and mineral phase makes them a useful indicator to quantify petroleum migration distance. Because of their nitrogen-heteroatom and annelated aromatic cycles they are generally regarded as being more resistant and the effects of biodegradation on their concentrations and distributions have not previously been investigated. Reservoir extracts from three wells located in the Leng43 block of the Liaohe Basin were analyzed to investigate their occurrence and the effect of biodegradation. Both hydrocarbon biomarkers and benzocarbazole isomers show systematical changes with the increase extent of biodegradation in study columns. Carbazole compounds may be biodegraded in a similar way to that observed in aliphatic and aromatic hydrocarbons. The distance from oil water contact is a primary control factor for biodegradation. The concentrations of benzocarbazole isomers show a slight increase in the upper part of the columns then a sharp decrease towards oil water contact (OWC). Among three isomers benzo[a]carbazole seems more susceptible to biodegradation than other two isomers and benzo[b]carbazole has higher ability to resist bacterial attack. Benzo[b]carbazolelbenzo-[a]carbazole ratios can sensitively indicate the degree of biodegradation and the benzocarbazole index (BC ratio) cannot be directly used as a migration indicator in biodegraded oils.

For improving the recovery of water flooding heterogeneous oil fields, the classical conformance control method is to enlarge the swept volume as far as possible, usually by fine layering, profile control and water shutoff, and fracturing and acidizing, etc. However, with watercut rising, the remaining oil distributes in deep reservoirs, making the classical methods less effective. “Sweep Control Technology (SCT)”, a new IOR method, is put forward. The whole production-injection flowing field is taken as the studying target. The waterflooding effect impacting factors were classified into three levels: large-scale macroscopic heterogeneity, middle-scale mesoscopic heterogeneity and pore-scale microscopic heterogeneity. Based on the impact of the three levels of heterogeneity on sweep efficiency, we developed new corresponding SCT materials. For large-scale heterogeneity, we put the materials in accurate place to effectively inhibit water flow prevailing channels. For the middle and small scale heterogeneity, the water flow is diverted to achieve effective sweep control by means of effective material migration. So that we can realize complete adjustment and control of the whole flowing field to achieve efficient remaining oil displacement, and to improve the recovery of water flooding phase. The research and experiments in laboratory and field have proved the advancement of the method.

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