Pertamina EP Java Region plans to complete several deviated wells in the Rengasdengklok field, onshore West Java to set casing on top of Mid Main Carbonate (MMC) formation. Pertamina EP faced a challenge when drilling into relatively low pressure carbonate reservoir in Rengasdengklok field. One of the major difficulties during the well construction was pinpointing the casing point at the boundary between the relatively high pore pressure overburden shale and the low pore pressure carbonate reservoir. The depth uncertainty and difference between the pore pressure of the overburden and the reservoir lead to circulations loss, kicks and blow outs.
Lost circulation in the MMC formation is a major risk to well integrity and safety. Total losses and kicks have been a main issue in the well planning and execution of the Rengasdengklok project. Also, with a reduction in hydrostatic head resulting from total losses, the formations drilled can become unstable that can cause stuck pipe. So it is very important to have 9 5/8″ casing shoe at relatively competent top MMC covering the Cibulakan formation.
The actual top of reservoir can be different than the top of reservoir obtained from correlation or seismic data. Thin carbonate stringers can be misleading and be interpretated as the top of reservoir and fracture shale can be a passageway for the drilling fluid into the reservoirs. Either too deep or too low drilling can be very expensive, harmful and bring unwanted consequences. Urging to manage the risks and lowering the possibility of any unwanted events bring Pertamina EP to look into new technical applications, the real time Logging While Drilling (LWD) Geostopping. The geostopping process is an interactive approach identifying geological criteria with real-time LWD measurements, combining technology and people to deliver optimally placed well bores in a given geological setting.
Sufficient offset data, paired with local experience of the involved geoscientists are essential for correct real-time decision. Therefore, the precise placement of the casing must be started from the planning phase.
The zero-offset bit resistivity was used in total of 4 wells from 2010 till 2012. The top reservoir was identified correctly at top of MMC formation. All supported well sections were stopped based on geostopping advice and any contingency casing was avoided. Some lessons learned have been applied and showing improvement in operational time. This procedure helped Pertamina EP to drill and stop exactly at the top of MMC formation.
Authors : Dimas Pramudito, Julianta Parlindungan Panjaitan