COMPLEXITY OF PORE PRESSURE AND STRESS ANALYSES IN MAHAKAM MEDIAN AXIS OF THE LOWER KUTAI BASIN, KALIMANTAN, INDONESIA.

摘要

The Mahakam Delta has been developed for more than 40 years and many wells have been drilled to develop the area and to increase production. The Tunu, Bekapai and Peciko Fields are located in the Median Axis of the Mahakam Delta and collectively have contributed a large volume of production. In the current context of mature fields, there are many drilling problems found, i.e. kick and lost circulation issues due to the reservoirs becoming more depleted, but on a positive note, isolated high pressure still exists. This complexity makes pore pressure and stress analyses in the research area essential in order to support the massive drilling and production activities in this area. The result of well data analysis shows that there are three pore pressure patterns in the study area, i. e. normal pressure, low over pressure and high over pressure. The analysis of cross-plot of sonic and density logs shows that low overpressure is generated by loading mechanism, while high overpressure is generated by non-loading mechanism. The loading mechanism is caused by relatively rapid sedimentation in the study area, while the non-loading mechanism is caused by kaolinite to illite transformation and gas generation. The analysis of pore pressure (Pp) and minimum horizontal stress (Shmin) shows that there is coupling relation, especially in the Tunu Field. This relation is proven by the increase in the hydraulic fracture value starting at the top of overpressure and by the presence of a lost circulation zone that coincides with the presence of a depleted reservoir zone. The coupling ratio of AShmin/APp in overpressure zone shows a relatively low value. This condition indicates that the overpressure is more the cause, rather than the effect of the increase in Shmin in that zone. This analysis will help to increase the understanding of pressure behavior in Mahakam fields, thus helping with a suitable well design strategy for further development and to unlock the remaining field potential.