A Modified Approach to Predict Pore Pressure Using the D Exponent Method: An Example from an Oil Field,South of Iran

The methodology for pore pressure prediction known as D exponent is a function of an exponent of adjustment that was originally defined for the Gulf of Mexico (Jorden and Shirley, 1966 Jorden, J. R. and Shirley, O. J. 1966. Application of drilling performance data to overpressure detection. J. Pet. Technol., 18: 1387–1394.  Google Scholar]; Eaton, 1972 Eaton, B. A. 1972. Graphical method predicts geopressures worldwide. World Oil, 7: 100–104.  Google Scholar]). A limiting factor of this methodology is the definition of the Normal Compaction Trend, which needs to be interpreted from the data (Mouchet and Mitchell, 1989 Mouchet, J. P. and Mitchell, A. 1989. Abnormal pressure while drilling. Manuals techniques 2. Boussens, , France: Elf Aquitaine..  Google Scholar]). In this study, the D exponent methodology was modified to make it applicable to the Gachsaran formation in an oil field of Ahvaz, Iran. The approach consisted of calculating the ratio between effective stress and the D exponent at each well, in order to find a robust NCT for the entire field, thus reducing subjectivity in the traditional D exponent methodology. Pore pressure determinations from Measured Direct Tests at one well confirm the predictive capability of the approach.