PI reservoir, the main reservoir of Daqing oilfield has an average thickness of 15-25metres with one-third OOIP of the total. This reservoir is highly flooded that their daily oil productivity is 4-5 tons /d per well, with a water-cut of 95%. But the current recovery degree of OOIP is only about 40 %, and one-third of the top thickness has not been tapped. Injected water circulating along the big channels can not further enlarge swept volume. In recent years, we drilled horizontal wells to recover the top remaining oil in the reservoir. Since muddy intercalation seldom develop within channel sand, this often results in fully flooded in horizontal wells by fast water breakthrough from the bottom to the topside of the reservoir as top remaining oil is produced. This paper describes reservoir with geological model, and shows the internal architecture in the reservoir accurately. We use lateral muddy intercalations as barrier beds to prevent vertical flood along the wellbore, Once flood occurs, we perform water-plugging in specific lateral beddings. Let's take well N1-H25 for example, it was designed as a horizontal well with vertical lateral beddings. It was brought into production in Dec, 2004, initially it produced 123 tons per day, which was 22 times the production of any well in the same formation. In July 2005, its daily oil production was 81 tons, with a low water-cut of 28.9%. It has accumulated 26000 tons of oil by Dec. 2005. This well was designed to pass 8 lateral beddings, but in fact, it passes 16 lateral beddings. Its lateral muddy intercalation successfully prevented water flood along the wellbore, and effectively produced potential remaining oil in top highly flooded sand reservoirs.
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