Publications

The focus of this paper is on the application of pressure data in building the stratigraphic framework for the Ranggas Field. Many wireline pressure data points were taken in the Ranggas Field in every well drilled. An analysis of those pressure measurements is the basis of this study. The work is part of a larger effort to construct a field-wide geostatic model in the absence of high quality seismic data. Rapid sediment deposition in the deepwater environment is one of the primary causes for the development of overpressured systems. In this setting, pore water in shales is unable to escape naturally during deposition. This process causes an increase in the pore pressure of the shales above normal hydrostatic pressure. Where shales are more widespread, the overpressure signature can be identified over a broader area, and hence, can be used to aid stratigraphic correlations. This work attempts to characterize shale intervals based on pressure groups in the vertical and lateral direction by comparing depth - pressure plots for individual wells and for sets of wells. Pressure groups are defined based on the amount of pressure increases between clusters of data. Shale intervals are identified from conventional log data (i.e. gamma ray and resistivity) which are then correlated to adjacent wells based on the similar characteristics of the pressure groups. It is assumed that all data in a pressure group originates from the same stratigraphic interval. For the Ranggas field, this analysis indicates the presence of a number of laterally-continuous pressure sealing shales that can be used for correlation. As found in this field, numerous thin shales, less than 100 feet in total thickness, have the potential to seal over an extensive area. In the absence of high seismic resolution, the recognition of these shales at different stratigraphic levels has provided a framework in which a more detailed well-to-well correlation can be made with confidence. Matching seismic picks with the correlated pressure data refines the seismic interpretation, especially in certain areas of the field that are geologically complex or poorly imaged.