THE ANALYSIS OF OVERPRESSURE GENERATING MECHANISM AND PORE PRESSURE PREDICTION IN ONSHORE AND OFFSHORE SOUTH MADURA AREA

• Main Author: WARMAN REKSALEGORA , SENA
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/20520
• Institution: Institut Teknologi Bandung

The analysis of overpressure generating mechanism and pore pressure prediction has been conducted in onshore and offshore of South Madura Area. The study area is located in the southern part of East Java Basin which is known to have overpressure zone. This area is also well known for its complexity in tectonic and sedimentation histories. Four onshore and offshore wells data and offshore 2D seismic lines were analyzed to meet the objectives of this study. <br /> <br /> Disequilibrium compaction is the main overpressure generating mechanism in the study area with minor contribution from unloading mechanism. The high sedimentation rate is the result of new local highs and accommodation space created by the compressional tectonic started in Early Miocene. Among the unloading mechanism, uplift and erosion dominate the contribution in the onshore well while clay diagenesis, hydrocarbon generation and hydraulic head have limited to none. Density-sonic crossplot shows limited to no clay diagenesis and all data are in the early diagenesis or Eodiagenesis. The analysis of source rock maturity report indicates that the source rock is still in immature stage which implies that there is no hydrocarbon generated in the penetrated interval which also supported by the temperature gradient. <br /> <br /> The pore pressure prediction was conducted using Eaton's and Swarbrick’s methods. By using Eaton’s exponent number of 1-1.5, the top of overpressure in the study area is estimated at the depth ranging between 300 ft to 3400 ft below ground level or below mud line. These numbers are within the range top of Fluid Retention Depth (FRD) or top of overpressure generated using Swarbrick’s method except for one well location. The prediction of top overpressure and pore pressure magnitude matches reasonably well with direct pressure measurement during and after drilling. The vertical and horizontal distributions of the top of overpressure in the study area are controlled by rate of sedimentation, well location and magnitude of uplift and erosion. <br /> <br /> A pore pressure model is proposed for future hydrocarbon exploration program in the study area and its surrounding. A detail analysis of future proposed well location with its degree of uplift and erosion is required to calibrate the proposed pore pressure model.