Application of Sequence Stratigraphy and Facies Analysis to Reservoir Development in Thin-Bedded Deltaic Sandstones; Example of the Giant Tunu and Peciko Gas Fields, Mahakam Basin, Indonesia

Bernard C. Duval, George P. Allen, Francis P. Mercier, Khaled Madaoui

The Tunu and Peciko gas fields (10 TCF of proven reserves) occur in a 2 km thick succession of upper Miocene deltaic deposits. Rapid subsidence and rising eustatic sea level resulted in a high accommodation rate and an aggradational stacking of thin (1-4 m) deltaic mouth bar sands separated by prodelta mudstones. Sequence stratigraphy and facies analysis integrated with RFT pressure and fluid data formed the basis for the reservoir layering and production strategy in the fields.

The succession exhibits a cyclic stacking of bar sands at several scales. The largest scale cycles are about 100 m thick and are believed to represent 4th order depositional sequences. These sequences are punctuated by maximum flooding surfaces with extensive marine mudstones. Because of the high rate of accommodation, the sequence boundaries consist of correlative conformities and occur within the most sand-prone intervals. RFT pressure data indicate that the maximum flooding surfaces form regional seals and that all the individual bar sands within a sequence exhibit identical pressure gradients so that each sequence constitutes a distinct fluid flow unit.

Sand facies and geometry of the Miocene bars are very similar to those of the modern Mahakam delta where individual bars amalgamate to form sand systems up to 10 km wide and 7 km long. Detailed studies of the modern delta have been directly applicable for determining well spacing and perforation programs.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995