Overpressure and Compaction in the PecikoField, Kutai Basin, Indonesia

摘要

The Peciko Field contains gas in multiple stacked reservoirs within a Miocene deltaic sequence. In thedeeper reservoirs, gas is trapped hydrodynamically by high lateral overpressure gradients. We haveanalysed overpressure and compaction in this field by using wireline log, pressure, temperature, andvitrinite reflectance data. The top of overpressure is located below 3 km burial depth, below the depthrange for transformation of smectite to mixed-layer illite/smectite. Density-sonic and density-resistivitycrossplots for mudrocks show unloading responses within the transition zone into hard overpressure below3.5 km depth. Vitrinite reflectance measurements indicate that the start of unloading coincides with theonset of gas generation. Moreover, mudrock density continues to increase with depth in the overpressuredsection. We conclude that gas generation and chemical compaction are responsible for overpressuregeneration, contradicting previous interpretations that disequilibrium compaction is the principalmechanism for generating overpressure in this area. The transition into hard overpressure may beidentified from reversals on the sonic and resistivity log responses in the mudrocks.