Interpretation of Shipborne Gravity for Gas Exploration in a Carbonate Environment

In 2015/2016 28,753 line kms of high quality shipborne gravity data were acquired in conjunction with an extensive 3D seismic acquisition program, offshore northwest Borneo.

The survey area is underlain by continental shelf platform and is characterised by extensive shallow-water carbonate development of Middle to Late Miocene age. The carbonate build-ups vary in thickness from several 100s of metres to over one kilometre in places at depths ranging from 750 to 2500m msl. Many of these carbonate build-ups have been mapped from seimsic data with numerous commercial gas discoveries, with over 65 tcf of recoverable gas reported to date.

Whilst there have been many successful wells drilled in the region, the remaining exploration potential in the block is considered to be of high-risk with moderate to low reward despite the low-cost associated with drilling relatively shallow targets. Here, the gravity data were interpreted to address two issues:

1.Can the gravity data be consistently used for regional and local identification of prospective carbonates?

2.By combining gravity, seismic and well log data would it be possible to predict gas presence in pinnacles to help reduce the number of wells drilled?