Publications

North Belut is a large gas field located in Block B, South Natuna Sea, Indonesia. The accumulation is characterized by a 1500ft gross section of stacked sands deposited in fluvio-deltaic environments within the Udang and Gabus Formations. The field was originally defined with 6 exploration and appraisal wells and is currently under a development drilling phase. The North Belut Field was part of a transitional succession that evolved from isolated rift basins to widespread shallow marine conditions (since Eocene time). The reservoir section was deposited in fluvial, deltaic, and estuarine environments. The clastic systems of the Udang and Gabus formations are predominately near shore deposits in fluvial deltaic to distal deltaic processes. These sediments show a high sequence frequency in an overall regressive system. These units are punctuated by sub-regional flooding surfaces. Clastic units of 1 to 25 m thickness are common in the 1500ft sedimentary column. Units of the Gabus thicken off structure to the north along the back of the paleo-structure. Detailed stratigraphic analysis combining well log and seismic data have been used to correlate the high frequency of the depositional cycles within the North Belut Field. The North Belut Structure is a paleo-high that was filled in during the post-rift phase of deposition of the Gabus and early Udang formations. A series of northeasterly trending deltaic to distal deltaic deposits developed along an NE trending axis north of the North Belut structure during the Oligocene. High frequency sequences were developed that range from distal deltaic to distributary channel deposits. Forced regressions have been documented. Sequence boundary 330 developed during the early syn-inversion time and represents a significant change of sediment input. Above sequence boundary 330, within the Udang Formation, the source providence shifted to the Sunda High to the SE. Depositional units of the upper Udang range from prodelta to deltaic. Mouth Bar sands in these upper units were deposited in at least two depocenters, but the sands generally pinchout downdip. This new look at North Belut addresses the complex stratigraphy and demonstrates how new data should be incorporated early in the development phase.