Abstract: The ultimate goal of scientific exploration is to discover and increase oil and gas reserves using the best way. The fundamental purpose of “four evaluations” is to find out oil and gas reserves at all levels, and the results of which are the establishment of the exploration knowledge base and the 3-D seismic models. The process of “four evaluations” is a process of deepening the understanding of geological laws and improving the exploration knowledge base and the 3-D seismic models increasingly, and it will work throughout the process of exploration for oil and gas. The standard system of “four evaluations” shows the workflow and standard of exploration theories, technologies, methods and all sectors in respect of target evaluations at four levels. So the traditional exploration mode is changed which is only based on experience, uses the shaft technology as the approach, and focuses on exploration engineering construction. A modern mode is set up, which depends on scientific decisions and comprehensive geological study, focuses on making benefits, and aims at establishing rational reserves sequence. Therefore, th e“four evaluations” can be regarded as the core of scientific exploration. Along with the progress of exploration theories and technologies, the content and method of “four evaluations” should be improved increasingly.

Key words: Daqing Oilfield, scientific exploration, four evaluations, oil and gas reserves, knowledge base of exploration