Hydrocarbon Occurrences in the Kandanghaur-Cemara Area, North West Java

Abstract

Abstract In the Kandanghaur - Cemara area hydrocarbons have accumulated in reservoirs of pre-Parigi stratigraphic units overlying the Pre-Tertiary basement. Lithologically the reservoirs are somewhat complex, consisting of volcanic tuff, conglomerate, sandstone and carbonate. Due to facies changes within certain stratigraphic units, the hydrocarbon distribution is discontinous laterally as well as vertically. Combination traps are characteristic of the area. Dealing with these kinds of traps, an optimization of the seismic field data quality and improvement of the data processing are simultaneously needed to delineate the accumulations more accurately. For a proper assessment as well as to avoid unneccessary condemation of the prospect, increasing the density of wells would consequently be very helpful. Structures seem to be related mostly to the relative downward movements of the piled sediments over the high - low pre-Tertiary basement fault blocks. In such cases the present reservoir depth then determines the maximum burial of the reservoirs. Geochemical analyses reveal that the hydrocarbons accumulated in the lower stratigraphic units (Jatibarang Volcanics, Lower Cibulakan) and also, most probably, in the upper units (Upper Cibulakan) originate from the Talang Akar section. Vertical fractures seem to be important for the hydrocarbon migration into the upper units. The high temperatures taken from Drill Steam Tests are probably related to the recent volcanic influence and are higher than the paleo temperatures indicated by maturation evaluation.