Abstract

Application of acoustic impedance generated from 3D seismic data has proven to be an excellent tool to identify reservoir distribution. The NE Betara-11 Horizontal Well, operated by Devon Energy in the Jabung Block, South Sumatra, had been proposed based on interpretation of an acoustic impedance volume. The well successfully penetrated the reservoir target and tested over 2000 barrels oil per day from a 975 feet long horizontal section.

The NE Betara field is the largest field in the Jabung Block that contains oil and gas reserves in sandstones of the Lower Talang Akar Formation. The Lower Talang Akar Formation provides high quality reservoir sands with up to 26% porosity and 1 Darcy permeability. The distribution of this high quality sandstone, which was deposited in a fluvial to estuarine environment, is very difficult to predict. The eleven wells drilled in this field would suggest that reservoir distribution varies drastically across the field. Pressure data and CO₂ distribution suggest that the field be made up of multiple compartments with different fluid contacts. This presents a major challenge to predict reservoir distribution and fluid content, and to recommend optimal drilling targets and well plans.

A cross-plot of lithology versus acoustic impedance from well log data revealed a strong correlation of sandstone to low impedance and shale to high impedance. The acoustic impedance volume also showed an excellent tie to the well logs.

These relationships allowed identification of the reservoir target and optimal wellbore design.

The NE Betara-11 well targeted a thick channel sand that is gas-bearing at an up dip position in the NE Betara-7 well and was predicted to be oil-bearing at the proposed location. The NE Betara-11 successfully penetrated the target sand and encountered the predicted oil column throughout the drilling of a 975 feet horizontal section. As a result of this well, the utilization of acoustic impedance has proven to be an effective tool for identifying reservoir targets and planning well trajectories in the NE Betara field.