Publications

This study aims to position a petroleum exploration target associated with an inclined oil or gas /water contact in exploration history. The discovery of the Peciko gas/condensate field in the Mahakam Delta Province, East Kalimantan, Indonesia, is shown as an example of this type of trap. Anticlinal theory is the most popular and reliable concept in petroleum exploration history. Hydrodynamic mechanism of entrapment of petroleum was established as an extension of the anticlinal theory with respect to the inclined contact (Hubbert, 1953).NWP-1 was a wildcat gas-discovery drilled in the Mahakam Delta Province in 1992. It tested a new exploration opportunity, based on hydrodynamic entrapment (Hubbert, 1953) in a closed structure that plunges gently northwards. PGH-1 and PCK-1 were previously drilled in the structurally highest area in the southern part of the prospect.An uncontrollable, overpressured zone and sub-commercial net-pays were encountered in the wells. Following the hydrodynamic theory, a hypothesis of gas/water contact inclined northwards was introduced to resolve the size-problem of its expected reserves.The hydrodynamic theory was reevaluated to examine generalization of the hypothesis in the area, based on a part of the 3D seismic cube and 16 exploratory wells available in 1996. Lambert, et al. (2003) shows a comprehensive description of the gas pool, and stressed that the trapping mechanism is related to the pressure gradient. They, however, did not show details of physics and reservoir sedimentology of the trapping in the deltaic setting. We, here, show a physical, sedimentological model based on the limited data set.Our results are: 1. Hydraulic heads and head-gradients are correlated to facies distributions of sand-and-mud with reference to the Modern Mahakam Delta. 2. Pressure gradients are related to movements of subsurface fluid (mainly water), and its surrounding structural lows are a probable overpressured domain. 3. The inclined contact of MF8-FS88 gas zones is explained not by the hydrodynamic entrapment but by a primary inclined piezometric surface due to the overpressured domain, structural control and spatial relationship of sand and mud facies. 4. We roughly estimate structural-axis-ward flow rate through the Peciko field and relaxation time of the overpressured domain that cause the pressure gradient over the Peciko field. A prospect of an inclined contact can be defined in an area where both an overpressured domain and a normally pressured one are identified.Keyword: Mahakam Delta Province, Peciko gas/condensate field, inclined gas/water contact, pressure-gradient, sand-mud facies distributions, overpressures, Hubberts hydrodynamic entrapment