Hydrodynamic Trapping, Tilted Contacts and New Opportunities in Mature Kutei Basin, East-Kalimantan, Indonesia

Jauhari, Usman; Permana, Robhy; Wijanarko, Andre; Soenoro, Ammireno
Resource Management, VICO Indonesia, Jakarta Selatan, Indonesia.

The role of hydrodynamic mechanism as a cause of tilted hydrocarbon-water contact has been discussed since 1950s. Source of the hydrodynamic forces are related to fluid flow by surface recharges from neighbouring highlands that move and tilt toward basin. Formation fluid flow expulsed from overpressured sediments in deep subsurface by compaction is also correlated as another trigger of the hydrodynamic forces. However, the idea of hydrodynamic role in tilting hydrocarbon-water contact is frequently challenged by an idea that the major role is lateral reservoir property variation such as permeability. The permeability variation causes lateral height difference of transition zone which is seemingly identified as "tilted contact". Kutei basin in East-Kalimantan in which acquisition of exploration and production data is very extensive provides a unique opportunity for an integrated analysis to help resolve the controversy related to the tilted-contact phenomena. The paper demonstrates how hydrodynamic mechanism plays a major role in generation of tilted contacts identified in the Kutei basin.

Gas-Water contacts (GWC) are identified tilted in series of deep sand reservoirs connected to overpressured shales in the Kutei basin. The tilting of GWC is strongly triggered by differential pressure gradient of water legs in opposite anticline flanks. Higher pressure gradient of water legs in one flank provides forces of hydrodynamic to push GWC to higher structural position than in another opposite flank. Center of gas accumulation becomes shifted from crestal anticlinal structure to flank area. In the meantime, shallow reservoirs unconnected to overpressured shales have flat GWC. Water legs in opposite anticlinal flank of the reservoirs are identified at normal hydrostatic condition. Similar pressure gradient in the opposite water legs does not provide energy to tilt GWC as in the overpressured-influenced reservoirs. The understanding of hydrodynamic roles in the tilted GWC has opened-up new opportunities for further development at flank areas.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012