Re-Discussion on Effects of Internal and External Pressures on Stability of Pipe String in Oil Wells

Reference1’s conclusions could be divided into two parts.First,traditional theory was negated,which had been analyzed and discussed in Reference2.Second,conclusions wee given as follows:"internal and external pressures have no effect on the stability of suspended pipe string;internal or external pressure itself has no effect, but its changes has effect on the stability of pipe string fixed at both ends".Through four calculation examples,it was proved that Reference1’s conclusion regarding suspended pipe string was only applicable to non-gradient pressure,but not to fluid column pressure or the combination of fluid column pressure and non-gradient pressure.According to logical analysis,it was confirmed that the conclusion on the pipe string fixed at both ends was contradictory,and it was incorrect that "internal or external pressure itself has no effect on stability of pipe string fixed at both ends".There was a serious mistake in the derivation of formula in Reference1,namely,"hydraulic pressure exists at the lower end of the pipe string fixed at both ends";the formula was very limited in use.Such mistake was attributed to non-recognition of the existence of fictitious force.