Historically, Dual Detector Pulsed Neutron (DDPN) technology has been used in Oil & Gas industry for cased-hole (CH) reservoir monitoring and as driver for production optimization activities. However, in challenging environments as thin layers characterized by low reservoir porosity and low formation water salinity, the standard DDPN interpretation jeopardizes the discrimination of gas and water bearing levels. This paper presents an advanced use of Multi Detector Pulsed Neutron (MDPN) tools integrated with open-hole (OH) data in order to overcome the DDPN criticalities providing a robust gas identification in such complex scenarios.
The methodology exploits the fact that, from DDPN to MDPN technologies, a series of technical improvements have delivered a more complete downhole data set. In detail, the MDPN tools currently available on the market offer the benefits of a more reliable petrophysical measurements self-compensated from borehole environmental effects. In addition, a higher gas sensitivity is guaranteed by using inelastic interactions and an optimized tool configuration including multiple detectors and longer source-detectors spacing. For a comprehensive reservoir monitoring aimed at production optimization in thin layers with low porosity and formation water salinity, the MDPN data are integrated with all the available OH logs and historical production.
The proposed workflow has been successfully applied in an Adriatic Sea gas well suffering from low hydrocarbon production where the aforementioned reservoir criticalities are worsen by downhole complex completion. In details, the through tubing MDPN acquisition allowed the identification of the potential bypassed gas bearing levels. Moreover, the integration with OH resistivity, density/neutron, nuclear magnetic resonance and dielectric logs supported the design of the final through tubing perforations strategy. The strong additional production (four times higher than previous one) confirmed the effectiveness of the described approach.
The integrated OH/CH methodology allows characterizing thin and low porosity intervals as pay zones. Such achievement represents an important milestone for the additional perforation strategy of existing wells in Adriatic Sea. As a natural consequence, the overall brown field gas production can be enhanced by widely applying the new technique without any increase in water-cut.