Vízügyi Közlemények, 1973 (55. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(96). THERMAL WELLS TENDING TO SALT INCRUSTATION, METHODS OF OPERATION by L. Bélíeky, Mech. Engr. (For the Hungarian text see pp. 398) In many of the thermal wells drilled in Hungary, the deposition of salt incrustations on the upper part of the casing is observed frequently and serious difficulties are encountered as a consequence. This incrustation is due to the precipitation of mineral salts dissolved in the water. Of these salts calcium carbonate is the most important component, which is kept in solution as long as the necessary amount of carbonic acid is available. Once this escapes, the calcium carbonate is precipitated and deposited on the internal surface of the casing pipe. The precipitation and deposition of salts occurs at different rates. In some wells it was found satisfactory to remove the salt incrustation on a few occasions annually, but in some wells this cleaning operation became necessary at 8 — 10 days intervals. Deposits are encountered, however, not only in the casing, but also in the horizontal pipe sections and in heating radiators following the well, which can be prevented from occurring by means of a heat exchanger. Salt precipitation over the upper part of well pipes is a long standing, all too familiar problem, due to which efforts to utilize the valuable thermal energy of the water for heating purposes, have been abandoned completely in some instances. One example for this in Hungary is the thermal well at Karcag, where salt precipitation in seen to be intensive ( Fig. 1 ) and the thermal energy is utilized in the vicinity. Control is possible by two approaches and accordingly the present paper deals with — the control of salt precipitation, in Chapters 2a and 2b, — the different methods for removing salt deposits in Chapters 3a, b and c. One of the effective methods of preventing salt from precipitating consists of "withdrawing" the point of salt precipitation from the well. The application of this method is restricted to wells which can be operated steadily at the pressure recognized as "critical" for salt precipitation. The schematical drawing and picture of the stabilizer operating at a well is shown in Figs. 2 and 3, respectively. The device marketed under the trade name "CEP1" and relying on the effect of the magnetic field proved unsuccessful in Hungary. One of the mechanical methods for removing salt incrustation involves the enlargement of the restricted pipe cross section by drilling. In the case of negative wells, this procedure is not without certain risks, since the material loosened by drilling may drop back into the well in quantities sufficiently large to block the inflow section. Owing to the great depths, this debris is extremely costly to remove. The periodic replacement in part or completely of the well pipe suspended into the casing may also be classified among the mechanical methods of control. The permanently erected drilling rig is shown in Fig. 5. The series of experiments directed at the removal of the salt incrustation by means of hydrochloric acid treatment has yielded positive results. The optimum application rate and ratio of HCl, and the necessary inhibitor for corrosion control were determined by this series of experiments. The acid-feeding equipment is shown in Fig. 6. As indicated by recent experiences, salt incrustation and consequent restriction of the pipe cross-section may potentially occur not only at 40 to 50, but down to 100 or even below 200 m depths. As an example the experiences gained with one of the thermal wells are described. The casing pipes of the well and the salt deposits arc illustrated in Figs. 7 and 8, respectively. Salt deposits occurred in this case not only in the producing pipe suspended down to 160 m depth, but also at depths below the shoe of the latter, down to about 250 m in the casing. From the experimental evidence available it was concluded that thermal waters have properties varying from well to well. For this reason each water must be analysed before acid treatment is applied. This analysis is obligatory for thermal waters from