This case study highlights the difficulties and challenges faced by a mature brownfield (40+ year field life and 330+ wells) producing via multiple offshore satellite platforms. Daily production issues include sub-optimal well-testing facilities, uncertainties in well performance, sand production, well flow assurance, gas-lift compressors uptime, bottlenecked pipelines and integrity problems. This paper showcases the journey of an operator in using portable high frequency MPFM well-test unit for closing the well-test data gap in offshore brownfields of Peninsular Malaysia. Here, the paper shares the lessons learnt and workflow for effective well-test data gathering and validation, diagnosing well performance using dynamic well behaviour recorded by high frequency MPFM, and subsequent well optimisation activities (such as choke optimisation, gas-lift optimisation and flowline de-bottlenecking) for rapidly improving well production. Moreover, this paper also highlights key findings such as related to PVT data input and how it can affect MPFM measurement accuracy. Ultimately, the use of portable high frequency MPFM has helped field operation to maximise oil production and arresting field production decline.