The dynamic behavior of sucker rod is described by wave equation with viscous damping in dowmhole diagnostic technique for sucker rod pumping wells. Based on the polished rod load and its displacement measured on the surface, the load and displacement of the sucker rod string at an arbitrary depth in the wellbore can be calculated and the dynagraph card at that depth can also be drawn up. Thus the working condition of pumping system could be analysed accurately.

The mathematical method and main functions of the downhole diagnostic technique are discussed in this paper. The method of torque calculation and parameter optimization required by field practices are also expounded. Finally the application of this set of techniques in Henan oilfield has been demonstrated also.

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