Abstract: The sonic velocity approach used to be applied for estimation of reservoir pore pressure. However, it doesn’t operate to Daqing oil-field with diversified current interlayer pressures. Following long-term waterflooding, the sandstone reservoir has variable spontaneous potential (SP) resulted from variable electrofiltration potential which is closed with the pressure drawdown. The SP approach is introduced from it. Taking the sandstone reservoir in Daqing oilfield as an example, this paper presents a SP approach applicable to interpret the sand pore pres-sure variations during the field development, based on SP log principle and capillary flow potential theory. It is indicated that as a new thought using this approach may improve the accuracy in the pressure interpretation, hence save a great amount of testing fees.

Key words: SP, pore pressure, well log interpretation, mathematical model, oilfield development