The disturbance of the temperature field in permafrost rocks when drilling gas wells

Results are presented from an analysis of the thermal effects at gas well drilling sites as observed at the Yemburg field in Russia. Field measurements were made during all the drilling operations, with the main source of drilled well temperature conditions being the observed time-temperature relationship of the drilling mud at the well inlet and exit during mud circulation. A hierarchical three-level model of the well drilling process was considered: the small-scale level uses as its characteristic time parameter the interval between two successive tool connections; the medium-scale level uses the period corresponding to one bit run; and the large-scale level uses the parameter of the duration of drilling for one pipe (including surface casing, intermediate casing, and flow string). Field information was processed by a consecutive stage-by-stage averaging of experimental data. The averaged data were compiled in tabular form with further mathematical simulation of the disturbance and restoration of the temperature field of permafrost rocks around the well. An example is presented showing a return of the phase transition front about one month from the end of drilling. 4 refs., 3 figs., 2 tabs., and a partridge in a pear tree