The Influence of Fault and Stress Contributed On Overpressure Mechanism For Neogen Formation (Mundu, Wonocolo, Ngrayong) East Java Basin, Indonesia

Rembang Madura Kangean Sakala (RMKS) fault zone and W-E structures of Kendeng Zone are the main structural elements in back arc basin, East Java, Indonesia. There are many perspectives about the overpressure zone at the basin. This research focus on the overpressure zone that related with formation and tectonic evolution. The study infer that high overpressure is explained by regional and local mechanisms. The results of analysis of log derived porosities at Karang Mudi-1 (KM-1) well indicate that high overpressure and overpressure was Neogen Formation (Mundu, Wonocolo, Ngrayong). Pore pressure prediction at KM-1 exerted Eaton’s method. There are two overpressure zones at depth 2.680 – 4.900 fTVD (B Zone) and 5.600 – 8.400 fTVD (D Zone). High overpressure D Zone are regionally caused by flexural structure (anticline and fracture) from transpression setting (West – East RMKS). High overpressure in KM-1 is transpression setting early which the overpressure follow the pop-up boundary. Area of high overpressure always related with fault thrust. Static mechanism is possible in the present day interplate stress field. Present the maximum horizontal stress was NEE – SWW. Local mechanisms occurs illitization at D zone from depth 6.800 – 8.400 fTVD. D Zone is unloading mechanism (illitization and lateral transfer open fracture).