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Currently the annulus pressure of gas well becomes more common, so the safe production of several wells has been seriously affected. The annulus pressure mechanism is relatively complex, and it can be approximately classified into annulus pressure induced by temperature effect, by ballooning effect and by leakage or seal failure etc. The article mainly focuses on the annulus pressure mechanism induced by ballooning effect and the corresponding calculation model. For the tubing column with two ends fixed and closed, when tubing internal pressure is larger than the external extrusion force, the external diameter of the tubing column balloons (i.e. ballooning effect). It reduces the annular volume between the tubing and the casing, and consequentially induces annulus pressure. Based on the fundamental theory of elastic-plastic mechanics, the tubing column is simplified into the thin walled cylinder so as to deduce the relation models between the internal pressure and its swell capacity and A annulus pressure value, which provide theoretical support for safety evaluation on annulus pressure and the next treatment program.

Oscillography impact properties were studied in four different temperatures. The research indicated that impact energy of sampled 4145H DC met the standard of“SYT5144-2007 Drilling collar” and “API SPEC7” in four different temperatures. With temperatures getting down, impact energy, crack propagation energy, and crack propagation energy/impact energy ratio decreased, cracking energy/impact energy ratio increased, crack propagation rate increased and dynamic fracture toughness decreased. In drilling, crack growth rate in DC was slow; the DC was not liable to fracture in normal temperature. On the contrary, crack growth rate was fast, as a result, the DC was easy to fracture in low temperature. The results provide reliable experiment resources for research on 4145H DC fracture. The research results provide reliable guidance for DC production and use in drilling and offer basic experimental evidence to the analysis of 4145H DC fracture mechanism.

During oil-drilling, the fractures of drill tool thread and piercement of drill pipe upset transition are very common in drill pipe failure as an object of petroleum and metallurgical researchers home and abroad. The classical fracture mechanics can only resolve the static fracture problem of oil country tubular goods (OCTG), but not resolve drill pipe failure under dynamic load. It is well known that the API 5D just prescribes strength criterion of drill pipe material but fracture toughness of drill pipe material. So, it is important to study dynamic fracture toughness of drill pipe material and present appropriate toughness criterion, which can not only optimize the drill string structural design, but also reduce fracture failure of drill string. On the basis of presenting main test means of dynamic fracture toughness and referring to the Charpy V test, the new impact experiment instrument is developed. Numerical and experimental comparisons show that the repeated dynamic fracture toughness tested by the impact experiment instrument is more accurate than one time impact, which can better show material characteristic and provide a reliable way to distinguish material characteristic, in the meantime, the correlations between dynamic fracture toughness of drill pipe material and failure of drill pipe is obtained.