Reservoir mapping: the latest development in well placement

Abstract

The PTTEP Australasia Montara development wells were recently drilled using a new deep-directional electromagnetic-resistivity tool, which enabled the simultaneous real-time mapping of multiple and varied geological and fluid boundaries in a thick reservoir, through the entire length of the horizontal section. Conventionally, geosteering is undertaken using borehole-scale measurements; data at this scale requires the wellbore to come in close proximity or cross a feature before it is detected. This scale of measurement is good for finer detail features but does not allow for visualisation of the geology beyond what it is measured at or just beyond the borehole wall. Nor does it enable a refinement of the geophysical subsurface unless at points of contact between the well and the feature that needs to be avoided. To bridge the gap between surface seismic resolution and measurements obtained at the borehole scale, a new deep-directional electromagnetic tool sensitive to variable resistivities but able to identify boundaries tens of metres away was required. The past decade has shown a significant development in resistivity measurement technology providing directional resistivity at a significantly larger scale than conventional logging tools. The first generation allowed wells to be placed proactively, removing the need to cross the boundary or be very close to it before it was identified. This latest generation of proactive geosteering tools has been developed to remove this gap, allowing for a refinement in geophysical/geological models and a new methodology in geosteering, moving the game from boundary to reservoir geosteering.