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Abstract Borehole stability is the key for successful underbalance drilling. In this paper, critical differential pressure calculating model for maintaining borehole stability and preventing blowout while drilling in underbalance condition is presented, using poroelastic and rock mechanics theory, and then, the principle for determining proper underbalance drilling pressure difference is put forward. Finally, using in situ stresses and rock strength parameters of well block ShiNan 4, critical underbalance drilling differential pressure of this block is calculated, according the result, the feasibility of underbalance drilling in this block is analyzed. Field application shows that theoretical results match the engineering situations very well, thus verifies the model.
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Received: 25 April 2003
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2003, Vol. 22 
