Publications

The recently drilled N-1 well by Pertamina EP Cepu Alasdara Kemuning in the Alas-Dara Kemuning Block in the East Java Basin benefited from advance logging suite to unravel tight, low contrast, hidden reservoirs not easily identified by common tools. The penetrated play of shallow-marine clastic of Tuban (Burdigalian - Early Miocene) and Tawun (Langhian - Middle Miocene) Formations have characteristics of tight, low impedance, low resistivity, low-contrast with limited to no density-neutron crossover, and sometimes high GR reservoir that difficult to identify with regular logging. State of the art logging selection is critical because these calcareous sands have high irreducible water saturations of 37 to 46%, medium to high porosity from 16 to 24 %, but low permeabilty up to 30 mD due to calcite and clay cementation associated with burial and tectonism. A selective combination of spectral GR, magnetic resonance, and resistivity imager logs helped the company find potential reservoir, differentiate payzone from residual zone with high water saturation, identify depositional environment, and optimize selective intervals for Wireline Formation Tester (WFT), Sidewall Coring (SWC), and Drill Stem Test (DST). In addition, the extremely large area packer of advanced WFT was deployed to measure formation pressures, determine fluid types and contacts, and obtain fluid samples in low permeability formation. In addition, the large-barrel rotary SWC was used to obtain core samples for routine and special core analysis. The integrated formation evaluation from open-hole logging acquisition along with fluid typing, fluid sampling, and core samples revealed the presence of hydrocarbon zones in both Tuban and Tawun sands. With low mobility information from logging in Lower Tawun and Tuban sands, the company was able to determine optimum DST intervals which helped the company uncover the potential hydrocarbon resources in this well.