At present, intelligent oil and gas facilities are using safety instrumented systems (SIS), distributed control systems (DCS), connected field instrumentation, historians, edge computing, and advanced analytics. Although the large amount of data generated can improve process safety, this benefit can only be achieved if the analytical integration still satisfies the required standards concerning independence, determinism, and assurance for safety functions. This article looks at how the SIS, the DCS, and the real-time instrumentation analytics can be combined so as to establish an evidence architecture that helps in the early detection of abnormal conditions, the evaluation of barrier health, the contextuation of alarms, and the provision of risk-informed support for human decision-making. A structured integrative review has been carried out in line with the PRISMA 2020 and PRISMA-S reporting guidelines in order to summarise the peer-reviewed and credible literature published between 2020 and 2025. The evidence is divided into five areas: functional-safety architecture, control and alarm management, instrumentation data quality, fault diagnosis and dynamic risk analytics, and cyber-human assurance. The synthesis shows that the most defensible design is not one in which the analytics control the SIS, but rather a layered architecture in which both the SIS and the DCS keep their present operational roles while authenticated, time-aligned, read-only data are sent to an independent analytics environment. This setup allows for predictive and contextual insights absent creating an unverified actuation path into the protection layers. The paper suggests an assured integration architecture and a five-level implementation maturity model. It concludes that the future value for process safety will depend less on the novelty of the algorithms themselves and more on traceable measurements, validated models, secure interfaces, explainable outputs, disciplined management of change, and clear human authority over safety-critical decisions.