Over a two-month period, contributed to the OPM/opm-common, OPM/opm-simulators, and OPM/opm-tests repositories by delivering eight new features focused on reliability, performance, and usability in reservoir simulation software. Work included refactoring error handling and message formatting in C++ to standardize diagnostics, optimizing Brine_CO2 calculations for computational efficiency, and improving parallel grid processing using OpenMP. Enhanced documentation and onboarding resources, updated simulation modules to support convective mixing, and expanded scenario coverage with new thermal gas-water simulation decks. Emphasized code safety through const correctness and reduced synchronization overhead, resulting in faster simulations, clearer error reporting, and more maintainable scientific computing workflows.