Publications

This paper discusses stresses that operate in the southern part of East Java Basin. The study area is located in Madura Strait covering an area of approximately 20,000 sq. km. The study integrated an extensive and well distributed data from 25 wells (mostly offshore and overpressure) and 5000 km of 2D seismic. It also included onshore and offshore wells near LUSI mud volcano. The study area is an eastern extension of Kendeng Zone and is well known for its overpressure as well as its complex tectonic and sedimentation. This study utilizes vertical stress (Sv) and minimum horizontal stress (Shmin) data to evaluate the subsurface stress condition. The magnitude of Sv is calculated from surface to total depth of wells by using density measurement from density log. The magnitude of Shmin is estimated using direct pressure measurement obtained from selected Leak-Off Test (LOT) and Formation Integrity Test (FIT). These tests are regularly conducted during drilling operation. The subsurface stress condition is defined using the magnitude difference between the two stresses (Shmin-Sv). Positive value in the overpressure zone indicates that Sv is not the main principal stress. The extensive folding and thrusting recorded in the seismic data clearly shows that the negative value does not necessarily represent Sv as the main principle stress. The preliminary result of this study demonstrates that horizontal stress or compressional stress is dominant and plays a major role in overpressure generating mechanism in the study area. Based on Anderson’s faulting classification, the distribution of the positive magnitude difference indicates that the subsurface stress condition in the southern half of the study area is generally a folding and thrust faulting stress regime. The northern half is likely a strike slip fault stress regime.