Integration of Pulsed Nuclear Saturation Logs for Monitoring Water Alternating Gas Injection

Aarseth, Nils-Andre (BP) | Tjetland, Gunnar (BP) | Daae, Victoria (BP) | Han, Xiaogang (BP) | Webster, Mike (BP) | Zett, Adrian (BP) | Quintero, Luis (Halliburton)



Saturation monitoring is a key component that requires special planning of reservoir management in a Water Alternating Gas (WAG) EOR process. Numerous factors have to be taken into account when planning surveillance, from fluids to filling history and compartmentalization. The alternating cycles are also important in determining when and where to gather the data.

Within the WAG EOR process itself, there are field specific drivers that ensure the miscible process delivers an efficient sweep. Quantifying saturation in WAG EOR is extremely challenging. We cannot treat this application as a simple three phase time lapse pulsed neutron problem. The end point values of various nuclear attributes will change with the fluids composition during production of the WAG cycles. Changes in water salinity, oil density, gas composition, pressure variation and deviation from compositional gradients will all potentially modify the notional end points. Access to “minimal” well and reservoir information will secure a robust saturation extraction from the application of multiple nuclear attributes. A more unique solution would require special modes of data acquisition, tool modifications or well conditions.

Well access can be challenging on a number of fronts from production deferral, limitations on personnel on board and costs of data gathering. Applying learnings from previous data gathering campaigns combined with evolving technologies in the area of multidetector pulsed neutron and memory conveyance can make surveillance in WAG EOR an efficient tool for reservoir management.

This is an arena where reservoir engineering and petrophysics needs to work together. This paper presents learnings from a Norwegian field under WAG injection and addresses the data acquisition, interpretation and integration within the reservoir model.