--> Real Time Geomechanic In Narrow Mud Weight Window And Uncertain Regional Pore Pressure; A Case Study Of Deep Water Exploration South Saubi-01 Well

AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

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Real Time Geomechanic In Narrow Mud Weight Window And Uncertain Regional Pore Pressure; A Case Study Of Deep Water Exploration South Saubi-01 Well

Abstract

Kangean Energy Indonesia (KEI), as part of exploration strategy, drilled South Saubi-1 exploration well with water depth of 3057 ft. South Saubi Field is located in the Block E, Kangean PSC, East Java Sea, Indonesia. In between year 1990 and 2000, there were five exploration wells drilled near South Saubi or Southern part of East Java Basin and these wells experiences numerous drilling problems such as kick, pack-off, BHA stuck, forced side-track and loss circulation occurred. These five wells are vertical well and the primary target was Prupuh/Kujung/Ngimbang reservoirs. The nearest offset well is ST Alpha-1 well is located about 42 km to the southeast from South Saubi prospect, this well shows that in Kujung Fm the well experienced total losses using mud weight of 10.5 ppg. On the other hand, toward northwest of South Saubi, Arya-1 well drilled and in Kujung Fm the well experienced kick and well flow which subsequently killed with 16.6 ppg mud weight. The other three wells Sawangan-1, Palung-1 and Baluran-1 shows mix between losses and kick in Prupuh/Kujung/Ngimbang Fm.. Hence, pore pressure regionally or in Southern part of East Java Basin, especially for Prupuh/Kujung/Ngimbang reservoirs is remained big uncertainty. Based on pre-drill geomechanical model which is build for drilling purposes, the worst case scenario is indicates very narrow safe mud weight window with little margin of error. Hence, thorough planning, efficient and safe drilling are essential for successful drilling campaign. Manage Pressure Drilling – MPD is also planned to be used in critical section in Prupuh/Kujung/Ngimbang reservoirs in order to drill safely in very narrow mud weight window. Real-time geomechanics services were employed to provide estimate not only safe mud weight windows that were bounded by pore pressure and frac gradient but safe and stable mud weight windows whereby breakout/collapse and breakdown mud weights were estimated in addition to pore pressure and frac gradient in order to avoid stuck, pack-off, tight hole, etc. Geomechanics engineers updating the pre-drill geomechanical model using logging-while drilling data: GR, Resistivity, Sonic, Density and Seismic that were streamed in real-time. Using these logs, pore pressure, breakout/collapse, frac gradient and breakdown mud weights were generated in real-time. These estimated mud weight window were analyzed and interpreted in conjunction with drilling mechanics, mud logs, cutting/cavings analysis, ECD and ESD for safe and stable mud weight recommendation. This window was further calibrated while drilling with LWD formation pressure measurement and leak-off test. Real-time update on safe and stable mud weight enabled several critical decisions like optimize casing depths and mud weight management. The South Sabi-1 well is eventually drilled safely with minor and manageable drilling problems.