Abstract: The marginal oilfield D in the Bohai Sea is faced with the reserve risks of reservoir connectivity and bottom water. And in order to solve the contradiction between the construction scale of engineering facility and the reserve risk, exploration wells shall satisfy the engineering conditions of converting into development wells in the late stage. In the stage of early research, exploration and development are considered overall, two exploration wells are deployed to test and evaluate the reserve risks, and the possibility of converting exploration wells into development wells is realized by modifying the test platform equipment and applying wellhead tieback and other technologies. And the engineering investment is reduced as much as possible by taking some measures, e.g. optimizing the number of risers and simplifying the wellhead protection frame. Based on the effective integration of different professions in the early stage, the exploration-development integration of offshore marginal oilfield is realized successfully, and the investment is applied to the targets definitely. The research results can be used as the reference and guidance for the development of similar oilfields.