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The AAPG/Datapages Combined Publications Database

Indonesian Petroleum Association


23rd Annual Convention Proceedings (Volume 1), 1994
Pages 245-259

Shale Compaction and Abnormal Pressure Evaluation Application to the Offshore Mahakam

Michel Bois, Yves Grosjean, Louis de Pazzis


Most of the wells drilled in the Mahakam Delta have bottomed in the pressure transition zone. As a result, several kicks and some internal blow outs occurred at the beginning of our exploration. In the Sisi field, located on the external structural axis of the Mahakam Delta, all the wells drilled encountered undercompacted shales. After a severe kick in one of the Sisi wells, unsuccessful past results were analyzed and a model taking into account the divergence between reservoir and shale pressures was established. A regional study of the shale pore pressures, based on the sonic logs, confirmed the frequent occurence of large discrepancies between reservoir and shale pressures. Shale and reservoir pressure evolution is associated to facies changes, especially in sediments deposited close to the shelf edge, as is the case in the Sisi field.

Shale pore pressure evaluation during drilling became a key parameter. The d' exponent plot was found to be the proper answer and was preferred to other real time shale pressure indicators such as MWD - LWD. Once the d' exponent plot is calibrated at the beginning of the run, it becomes a reliable shale pressure indicator.

The generalization of this method to most of the exploration and delineation wells drilled in the offshore Mahakam, allows both rig time saving and a better safety while drilling.

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