Publications

Seismic and sequence stratigraphy played a prominent role in two Unocal regional studies of the Lower Kutei Basin (Fig. 1) undertaken between late 1991 and the end of 1994. Prior to these studies, field-to-field and exploration ~ 1co1rrel ations in Unocal's PSC blocks in the Lower Kutei Basin were difficult, even after 20 years of exploration. This was due to widely separated Unocal licences, lateral discontinuity of deltaic sediments, and local structural complexity. As a consequence of these limitations, meaningful regional maps, facies predictions, and interpretations of structural evolution could not be made easily.Unocal and other operators in the Lower Kutei Basin recognized the need for a regional stratigraphic framework and have separately undertaken, or are in the process of completing, regional stratigraphic studies in the context of sequence stratigraphic models. Some of this work has been published (Duval, et al., 1992, Van de Weerd and Armin, 1992, Malecek, et al., 1993, Saller, et al., 1993). In addition, studies of the modem Mahakam Delta system by Total Indonesie (c.g., Allen et al., 1976, Allen and Mercier, 1994) haye been of fundamental importance in understanding the facies architecture of the basin.The objectives of recent Unocal studies were to: (1) provide a chronostratigraphic framework to facilitate inter-field correlation in offshore and adjacent onshoreareas, (2) map the regional facies distribution and determine the role of stratigraphic entrapment in existing fields that were recognized originally as structural traps, (3) identify significant tectonic and depositional events that may have influenced development of petroleum systems, (4) define the major petroleum systems in the basin, and (5) apply the results to exploration in undrilled areas or where obvious structural traps have already been tested or are absent. The last objective is ongoing.Data utilized for these studies consisted of about 150 wells for correlation and facies analysis. Calcareous nannoplankton and forams were identified from about a third of these, and palynomorphs were identified from 10 wells. Seismic lines were selected from thousands of kilometers of data shot by Unocal, or obtained by trade from other operators. The seismic lines available were shot in many different surveys beginning in the early 1970s, and an attempt was made to use the most recent ones available.As a result of these studies, local and regional correlation (Fig. 2) has improved significantly along with predictability of facies and the interrelationships between structures and sedimentation. Most importantly, the regional perspective provided insights into reservoir architecture and petroleum systems that have impacted prospect development in Unocal's current drilling program.