Seismic Correlations of Well Markers in Difficult Settings -An Example from the Nelson Field - Forties Sandstones

In settings characterized by erosional features and sediment infill, mapping unconformities, or sequence boundaries at intra-reservoir levels is the key to building accurate reservoir models. In many such cases, unconformities can be picked reliably in wells. However, correlating these markers from well-to-well on seismic data is challenging. Conventional horizon auto-trackers cannot be used because the seismic response along unconformable events varies laterally. In some cases unconformities can be drawn manually but this is a time-consuming task that, at best, generates inaccurate surfaces. As the complexity of reservoir architecture increases manual drawing becomes more challenging and practically impossible.

In this paper we present a study performed on the Nelson Field as an example of a new method for correlating wells at intra-reservoir levels on seismic data. We use an inversion-based algorithm to create a dense set of horizons that fits exactly at important well markers. The method consists of two steps:

1. With the help of an “unconformity tracker” a set of intra-reservoir framework horizons are produced, which fully honour the well markers.
2. Using a similar inversion-based algorithm a dense set of horizons is created in between the framework horizons.