Predicting the Hydrocarbon Limit on Peciko Unconventional Trap Giant Gas Field

Abstract

Peciko is a mature giant multilayer gas field, located in the offshore area of Mahakam Delta, Indonesia. The field has been in production since 1999 with more than 150 development wells drilled. The first exploration well (Peciko-1) was drilled in 1983 in the crest of Peciko anticline. Although it found only insignificant gas bearing in a mostly poor quality reservoir and high pressure, this well proved that the hydrocarbon trapping system was worked. The 2 well, Northwest Peciko-1 was drilled on 1991 in the flank of the structure and hit more than 200-meters gas net pay. Realizing the potential of an unconventional trap with potential gas column up to 240-meters, 19 more delineation wells were drilled and finally confirmed the presence of giant gas accumulation with hundreds of individual sand bodies distributed in about 1500-meters gross intervals. The thickest net pay accumulation was located in the flank of the structure, while the crest was mainly constituted by high pressure water bearing reservoirs. This was interpreted as a counter pressure mechanism due to an active lateral S-SE directed compaction water (from higher pressure zones) flow conveyed between flooding surfaces through the pay zones and down-dip across syncline towards the lower pressure zones, while the circulation of compaction water was diverted around the trap.

An observation on the stratigraphic cycles concludes that there is a correlation between regressive and transgressive sequence versus distribution of gas accumulation and gas in place volume. In the regressivetype reservoir, reservoirs are generally more widely connected, while in the transgressive-type reservoir, over the same stratigraphic interval may contain several hydrocarbon pools, it is very likely due to the reservoirs size are relatively small and rather detached. By carefully applying the tilted-contacts conceptual, where it defines a hydrocarbon pool limit as an equipotential pressure (water head) on a given equipotential map (U-map), therefore the hydrocarbon accumulation limit of this mature field could be predicted more reliable (when the hydrocarbon filling ratio equal to zero on a given equipotential map). Moreover, adopting the methodology where the tilted-contacts occurred, into multi-layer Peciko reservoirs depending on the degree of its certainty on contact and fluid interpretation, it is now possible to see the extension of the hydrocarbon accumulation limit towards the step-out perimeter of this mature field, and thus, opening a new possible area for future delineation targets in Peciko field.