Abstract:

Over years of waterflooding development, the water injection pressure has been increasing and the water injection pressure has been decreasing while the effect of acidizing treatment becomes worse, resulting in long-term insufficient injection, large formation pressure drop and rapid production decline in Bohai B oilfield. In actual water injection process, near-borehole pollution may occur and cause additional pressure drop. The injection pressure limit available at present was designed at the early waterflooding development stage, which cannot adapt to the current conditions, so it is urgent to research how to optimize the injection pressure. In this study, after introducing the theory of additional pressure drop, the actual water injection pressure differential was calculated based on fluid mechanics, the theoretical dimensionless water injectivity index was derived, and finally the theoretical water injection pressure differential was obtained. The accuracy of the calculated additional pressure drop was tested in wells with the results of pressure-drop well testing and acidization, and the reasonable water injection pressure was optimized. The result provides basic data for later water injection while increasing pressure. Depending on field equipment conditions, 23 well-time of water injection while increasing pressure have been implemented in B oilfield, which on the one hand, has saved acidization cost, and on the other hand, maintained oil production. It is helpful to improve the ultimate recovery in the oilfield.

Key words: offshore oilfield, waterflooding development, Bohai B oilfield, water injection pressure, additional pressure drop, dimensionless water injectivity index, water injection while increasing pressure