Abstract. Exploration in the Mahakam coastal and offshore areas, first focused in the 1970's on structural targets, led to the early discovery of several giant oil and gas fields. As ensuing production began to decline, a regional synthesis of the basin was undertaken to evaluate the remaining hydrocarbon potential. This program focused on sequence stratigraphy and the petroleum system approach, and required several years of effort. As a result, a new type of stratigraphic play was defined and successfully drilled, quickly appraised, and recognized as a gas giant, named Peciko Field.
Simultaneously, sedimentological observations of the modern Mahakam Delta and its close relationship to the underlying Miocene Delta, strongly suggest that subsurface thinly bedded productive sandstones would be widespread and continuous reservoirs. Systematic pressure analyses were utilized to assist in the understanding of the hydrodynamic effects within the developing Tunu Gas Field, and to expand this concept throughout the basin. The interplay between the regional study and the geological, reservoir, and production knowledge derived from the two developing fields enhanced the reserve figures for those fields, and had a direct bearing on their highly and increasingly efficient drilling appraisal programs. 3D seismic helped identify gas sands in the distal faulted setup of the basin, and is expected to contribute greatly to the ultimate understanding of hydrocarbon accumulations in the Mahakam.
The ‘creaming curves’ illustrate the early high level of maturity reached for oil discoveries in the Mahakam.
Fifteen years later, the maturity for gas discoveries is far from levelling out, thanks to a new working model that has changed the long term future of the province.
1. INTRODUCTION The Mahakam Delta area is part of the Kutei Basin, located in Kalimantan, Indonesia, on the eastern coast of the island of Borneo. It is a very old petroleum province, where production started one century ago. However, the swampy coastal plain and the adjacent offshore area remained untouched until they were opened to the industry in the late 1960s.
A new cycle of oil and gas discoveries took place thereafter, utilizing seismic technology to locate structural closures. Production from these fields began to decline in the early 1980s.
A second cycle of exploration, starting in 1986, reversed the trend of production decline. This cycle produced mainly natural gas discoveries, and was the result of incorporating new concepts, stratigraphic and other techniques, into exploration.
The Mahakam case, well documented over 25 years of exploration and production, represents a balan