Marginal oil fields refer to some small and medium-sized oil fields or oil fields with complex stratigraphic structure and located in remote areas. There are more than 100 large and small blocks marginal oil fields with huge reserves. They have the characteristics of geological reservoirs such as structural fracture, fault development and complex oil reservoirs. The development is uncertain and is not suitable for excessive investment. How to carry out economic and effective exploration and development of marginal oil fields has become a new breakthrough in stabilizing production and improving benefits in A oilfield, as the first marginal oil field with “extended test of development evaluation wells + overall development plan”, designed and manufactured three hole asymmetric underwater wellhead base plate in combination with mudline hanger in order to meet the needs of overall oilfield development, Realize the temporary abandonment of the extended test well after the test, and put it back into production in the overall development stage of the oilfield. It provides a new mode of cost reduction and efficiency increase for the subsequent development of marginal oil fields, which will revitalize a large number of marginal oil fields to be developed and bring huge economic and social benefits. The establishment of a safe risk response mode of “advance can be attacked and retreat can be defended” can improve the efficiency of preliminary research and avoid the risk of oilfield development.