A Comparison of Pore Pressure Profiles in Pattani Basin, Gulf of Thailand

Abstract

Abstract

The Pattani Basin lies in the south of the Gulf of Thailand to the north-northwest of the Malay Basin. From previous well experience, pore pressure profiles in the Pattani Basin can vary thus making drilling problematic.

For instance, in well A, reservoir pressures increase above hydrostatic in the D-E formations and mud-weight increases. Both reservoir pressure and mud-weight gradually continue to increase towards 13 ppg to the N-O stratigraphic intervals.

In well B, mud-weight follows a similar high trend to the previous well, but, by way of contrast, deeper reservoirs e.g. J-K, are only slightly above hydrostatic and the deepest reservoirs N-O, at the same depth as in well A, are normally pressured. Losses are a problem. Analysis of sonic, resistivity and density data from each well suggests that the shales have similar properties (and therefore pressures). Similar pressure profiles have been observed in the Malay Basin and East Java.

These observations clearly present an issue for future well planning as these differences mean that it is problematic to predict whether the reservoirs encountered will be normally pressured or overpressured.

A solution may lie in analysis of fault seal and overall stratigraphic net to gross. Both of these wells lie close to faults of similar strike but variable throw (high/low). Also the well to the north, well A, has a higher overall shale volume throughout the well interval. This suggests that although shale pressures may be similar in both areas drilled, reservoir pressures are less likely to drain off laterally through faults due to permeable juxtaposition in the well in the north.

This paper highlights the generation of these pressure profiles in terms of integrating log and drilling data. Following this, we construct a plausible geological model to reconcile the reservoir pressure differences.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016