Abstract

The Ibul Field is located in the Contract of Work Extension Area in South Sumatra. The field is a domal feature where structure is the primary factor for the control of the hydrocarbons but stratigraphy is also important. The oil is reservoired in the Talang Akar and Lemat Formations.

Drilling in the southern part of the field was initiated in October of 1982 with the completion of Ibul-40. The objective sand was not developed at this location but another sand was encountered that had twenty-three feet of net pay. The well flowed 951 barrels per day of clean oil on an initial test.

Additional wells were drilled to evaluate a concept that is based on the concidence of two trends of geologic and seismic data that form distinct geometric patterns. In the continuing study of Ibul Field point-bars were recognized as the most important reservoirs. An anomalous low frequency seismic event was mapped that coincided with the occurrence of the point-bars. This anomalous event has been interpreted to be caused by a reflection from the point-bar sands being out of phase with the strong Basal Telisa Limestone reflection.

When mapped, this anomalous event was found to form a linear pattern that had the configuration of a stream channel; hence the name "Seismic Channel Anomaly".

A sand percent map of the Upper Talang Akar Formation shows an almost exact coincidence between the configuration of the "Seismic Channel Anomaly" and the highest sand percent trend. The anomaly is interpreted to represent a stratigraphic accumulation distinct from those in the Ibul Field proper.

Several additional wells drilled in the south southwestward extension of this anomaly have found new reservoirs and additional reserves. More wells are needed to define the potential of this stratigraphic play. More important, the integration of geology and geophysics is essential for defining elusive stratigraphic accumulations that, given the proper setting, can add substantial reserves.