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A Re-determination of Besitang River Sand Reservoir, Using Electric Facies and Neural Network Approach, Besitang Field, North Sumatra Basin, Indonesia

Bob Wikan H. Adibrata1, Muharram Jaya Panguriseng2, Ory Sadjati1, Zulkifli Abu Bakar3, Indra Shahab3
1 Pertamina Upstream, Jakarta, Indonesia
2 Schlumberger Information Solution-Jakarta, Jakarta, Indonesia
3 Pertamina Upstream, Rantau, Indonesia

Besitang River Sand (BRS) is one of the prolific hydrocarbon-producing in the North Sumatra Basin, Indonesia. Developed as a submarine fan, lateral discontinuity of BRS is one of the problems in developing Besitang Field, reflected by some dry holes at the top of the structure, whereas producing wells reside on the flank of the closure.

The variety of sand in BRS showed by the differences in spatial pattern that reflects the facies change in sand within the BRS. Detailed electric-facies definition and correlation in BRS was conducted using 25 wells from Besitang Field and surrounding area, calibrated with cores, cuttings, and biostratigraphy analysis, and also supported with re-interpretation of 2D seismic data of the area.

Four sand facies were identified, from base to the top are; (1). Very fine to fine sand facies, (2). Medium to coarse grained sand facies, (3) Interbeded-sand and claystone facies, and (4) Channel-fill sand, fine to coarse grained sand facies with coarsening-upward log's shape.

Lateral definition of sand facies was carried out using neural network approach, where some exploration wells with relatively complete data set were selected as model or training ground. The calibrated models were then used to predict and to propagate sand facies for the rest of the wells in the field. This new facies type determination and distribution, changes the development concept of BRS in Besitang Field, resulted in some new in-fill drilling locations and some new intervals that need to be perforated and tested.