ASP(alkali surfactant polymer) flood was initiated on March 15, 1997 in N-1DX block in Daqing oilfield; its main slug was completed on June 12, 1999. By September 23, 1998 pump malfunction occurred with a scale thickness of 1cm over in well bore. By the end of 1999, a serious scale was found in surface gathering and delivery system, with a 0.3cm of scale thickness found in single well pipes, gathering pipes as well as in heating furnace, this unfavorably affected current production.

In terms of this problem, we performed study of scale removal and inhibition.

  1. Analytical study over scale content, scale forming mechanism and regularity.

  2. Chemical agent study of scale inhibition.

  3. Study of physical scale prevention method, and we performed comparison test on different well respectively, using coated nickel, three layered compound coated pipes and ordinary pipes.

  4. We used hydro-electrical scale preventing unit, magnetic scale preventing unit in oil gathering pipes.

Through tests of the above methods in different wells, we obtained a satisfactory effect, the chemical agent method prolonged the pump check period from 30 days to 109 days; the coated pipe scaled slightly or didn't scale, and the scale was physically loosen. With these methods combined, scale prevention performed a good effect in well bores, single well pipes, oil gathering pipes and heaters. It ensured a conventional production in tested area. This paper presents the study of scale forming methods, the process of scale inhibition and the ideal effect we obtained.

Brief Introduction of ASP Test in B-1DX Block

This block lies in the N-1DX Block of Daqing Oilfield, its two central wells are B1–6P34 and B1-D6-GP127, 6 injectors and 12 producers in 5-spot well pattern, with a spacing of 250 meters, the area is 0.75km2, its target layer is PI1–4 layers.

ASP flood was initiated on March 15th, 1997; the main slug was finished on June 12th, 1999. The supplementary slug plan was finished on September 11th, 2000. On June 1st, 2002, all the chemical slugs were finished and succeeded with subsequent water flood. The end of 2003 injected 0.187PV of the pore volume in reservoir.

The ASP flood obtained remarkable incremental oil and greatly decreased the water-cut. By the end of 2003, the whole pilot area accumulated 299.5 thousands tons of oil production, with an incremental oil of 167.438 thousands tons. The accumulated oil production of the central wells reached 46.283 thousands tons, with an incremental oil of 27 thousands tons. This obtained a 21.51 percentage of more oil recovery than that of water flood.

Scale occurrence and its bad affection to production in 1998

Serious scale in lifters unfavorably affected production

After 0.243PV of pore volume was injected in September 1998, a serious scale was founded as the pilot entering its peak period of response. Since the central well N1–6P-34 occurred a malfunction of pump by scale on September 23, 1998, 12 pump checks or replaces were performed, the shutdown period reached 114 days, with a 6081 tons of oil production was affected. When restart the pump after a stop, the pump malfunction often occurred; the scale on submersible electric pump (on its separators and vanes) decreased the pump efficiency. Side wells entered its peak period of response since the end of 2001; a serious scale was founded in well bore too.

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