With the gradual progress of drilling to the deep layer, the formation conditions become more and more complex. The safe density window of drilling fluid is narrow, and well kick and overflow occur frequently. Aiming at this problem, this paper proposes an overflow evaluation index - overflow formation energy. From the perspective of energy analysis, overflow is regarded as the process of formation fluid doing work on the wellbore, and the power of overflow work can reflect the strength of overflow, so this power is defined as the overflow formation energy. Based on the model established in this paper, the effects of different types of overflow fluid, invasion rate of overflow fluid, drilling fluid density and formation pressure coefficient on overflow formation energy are analyzed. The overflow formation energy of gas is the highest. As the invasion rate of overflow fluid increases, the energy of overflow formation gradually increases. The data of 7 overflow wells are analyzed, and the corresponding overflow formation energy is calculated. It is found that the throttling circulating well killing method is more appropriate when the overflow formation energy is small. The overflow formation energy can quickly evaluate the overflow situation, provide theoretical basis for well control operation, and reduce the probability of well control operation risk.

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