ABSTRACT: Structural and petroleum systems modelling of the Eocene Ngimbang-sourced petroleum systems of the eastern East Java Sea. Part 1: Structural development

Matthews, Stephen J.¹ and Andrew S. Pepper²
(1) BP Amoco, Middlesex, United Kingdom 
(2) BP Amoco, Houston, TX

The East Java Sea basin underlies the East Java Sea shelf and its extension into deep waters north of the islands of Bali and Lombok. The present day basin structure has evolved in response to late Neogene and Pleistogene inversion of an Eocene back-arc rift system.

Following an early extension event of poorly constrained age and distribution, the primary source (Ngimbang coals and carbargillites) and reservoir (Ngimbang clastics and carbonates) were deposited in a widespread transgressive post-rift sequence. The main seal (Ngimbang mudrocks) was deposited following a renewed pulse of rifting during the Late Eocene.

Serial structural cross-sections have been constructed along the length of basin. These have been restored sequentially, incorporating erosion estimates from 1-D basin models, to assist understanding of trap development vs. accumulation of overburden in kitchen areas. Back-arc contraction during the late Neogene to Pleistogene created the major present-day structural culminations by reactivation of several major precursor faults and uplift of their hangingwalls. The effect of this contraction in shallow water shelfal areas, where marine and subaerial erosion processes were effective, was to exhume locally maturing source rocks from their graben kitchens. Effective kitchens for these inversion structures were restricted to areas where continuous burial of previous footwall / platformal areas was adequate. In deeper water, inversion structures grew without significant removal of overburden; many of these systems are experiencing maximum burial and hence thermal stress at the present day. Extensive kitchen development is however restricted as a result of the relatively limited late 'post-rift' deposition.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia