Search

Using the first principles method, which is based on the density function theory (DFT), the structures and electronic properties of S atoms are adsorbed on the Fe (100) surface for X(X is Cr, Ni, Mo, C, Mn ,Si,P and S) impurities in Fe, and their molecular orbital and absorption energies were calculated with the generalized gradient approximation. The results show that S adsorbed on H site for Cr, Ni, Mn, C and Mo impurities in Fe is stable but for Si, S and P is B site. The adsorption energy for Ni in impurity Fe is almost nearby for the purity Fe and the effect for Ni in S absorption on Fe (100) surface is very small. In order to prevent S absorption on Fe surface，we can reduce the percentage of Ni.

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 the process of deep drilling with high temperature and high pressure, downhole drilling tools might be exposed to various corrosive mediums, such as water/oil-based drilling fluid systems, dissolved oxygen, H2S/CO2, halogen elements (Cl- and Br-), etc. Halogen elements existing in the drilling fluid are ions promoting corrosion of metals. This effect is mainly manifested in the forms of uniform corrosion, pitting corrosion, stress corrosion cracking, etc. of carbon steel. Quality of the drill pipe is determined by the DP body, joint and welding area of the drill pipe. Reasonable friction welding process and proper post weld heat treatment can make the mechanical property of weld joint satisfy related standards. If process of friction welding or post weld heat treatment is improper, the weld joint will be easily damaged and accidents of pricking, breaking, etc will be likely aroused. This paper carries out an evaluation experiment of chloride cracking on the DP body, joints and weld joints of the high-strength drill pipe (S135) and discusses corrosion of the high-strength drill pipe caused by chloride ions.

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.

The exploitation of high acid wells is facing severe corrosion challenges in the A and B gas fields in Sichuan, thus using lined steel pipe is a reliable and cost-effective anti-corrosion measure. However, lined steel pipe welding involves dissimilar steel welding, and anti-corrosion performances will be affected if the welding process is unreasonable. So it is necessary to make evaluation for corrosion of lined steel pipe. In this paper, taking welding gap of L245/825 lined steel pipe as example, the anti-SSC performances of L245/825 straight and ring welding gaps in NACE A solution were studied by CR method, and anti-cracking performances of them were evaluated by laboratory experiments. Then corrosion performances of L245/825 lined steel pipe welding gaps and L360NCS carbon steel were studied in the corrosive environment found in the Tian Dong 5-1 high sour gas well. Laboratory and field tests show that straight and ring welding gaps of L245/825 lined steel pipe have good anti-environment and anti-cracking performances of electrochemical corrosion in the high acid environment. The technology of welding process selected in the paper is reliable. Research results provide references for welding operation of L245/825 lined steel pipe in high sour gas fields.