Comprehensive Usages of Multi Detector Pulsed Neutron Logging Tools to Overcome Mature Field's Challenges: Case Study from ACG Field

Abstract

Effective reservoir management of mature fields hinges on sustaining production. In most cases, the reservoir conditions differ from the initial measurement at virgin environment. The Azeri-Chirag-Gunashli (ACG) field, a substantial asset located in the Caspian Sea, Azerbaijan, has been developed over more than two decades. With the development of the field, production of reservoir has gradually shifted from Fasila thick uniform sand bodies to Balakhany heterogenous formation. Understanding the changes in the reservoir caused by down flank water and crestal gas injection is pivotal for the success of reservoir development. Addressing contemporary petrophysical surveillance challenges, Multi Detector Pulsed Neutron (MDPN) technology emerges as a key solution for saturation measurement through casing or surveillance in complex logging scenarios. Challenges may stem from uncertainty of formation water salinity, complex logging environments, complexity of formation lithology, etc. Historically, MDPN is mainly used to measure hydrocarbon saturations by utilizing petrophysical measurements such as formation sigma, C/O, etc. MDPN also furnishes crucial data on well integrity. For instance, open hole gravel pack, a prevalent completion in ACG to prevent the problem of sand production. An innovative pack quality surveillance has been developed, benefiting from pulsed neutron logging technology. This paper describes the workflow developed for matured field independent of service providers and presents real-world instances of measuring hydrocarbon saturation behind casing. Challenges of using pulsed neutron logging tools in complex logging conditions, such as saturation in open hole gravel pack completion, logging through multiple tubulars, formation lithology effects are also demonstrated and discussed. While saturation garners more attention, well integrity is another main usage of pulsed neutron logging tool, which unfortunately is less explored when compared to saturation. In ACG, Pulsed neutron logging tool is also widely used for Gravel Pack Evaluation (GPE), water flow detection behind casing. Combining reservoir and well integrity surveillance is an efficient way of logging for comprehensive interpretation to address reservoir management and well health diagnostic applications. Logging program optimization can significantly reduce operation cost and maximize the value of MDPN logs. For instance, extracting the baseline saturation logs from GPE surveillance and pack information at high logging speed are also demonstrated in this paper.