ELECTROMETRIC OBSERVATIONS OF ANTIFILTRATIONAL CEMENTATION CURTAINS *

Creation of antifiltrational cementation curtains needed to prevent increased seepage from water reservoirs is a rather labour-consuming and costly measure. High cost of such curtains necessitates careful checking of the quality of cementation as well as the strength and stability of the solidified cement which is being formed in the pores and fissures of injected rocks. The traditional methods of control are rather labour-consuming and do not allow observations during process of cementation. The advantage of electrometric observations of cementation curtains lies in the possibility of making measurements on the surface from the moment of pumping slurry into a borehole up to the termination of cement hardening. The laboratory investigations carried out by the authors demonstrate an increase in the specific electrical resistivity of a cement in the course of hardening as well as the existence of a functional dependence between the electrical and strength parameters which allows to use the resistivity method for checking the cement strength. Methods of electrometric observations of cementation curtains are dependent on the particular features of cementation and the curtain dimensions. The observations are usually conducted in a network of profiles parallel to the curtain axis. The cement slurry spreading in the space is studied on the maps of ρ_a and geoelectrical sections obtained at different distances from the feed line. Zones of the strongest absorption of cement slurry are indicated by resistivity minima. The electrometric observations should be compared with the data on cement expenditure in the boreholes. The cement strengthening is monitored by comparing the results of control observations consecutively conducted in 1-2 months following the cementation, with utilization of the ρ_a maps and graphs. If the specific resistivities of the skeleton of the enclosing rocks and the filler of cavities are known, one can approximately evaluate the changes in the cement strength in absolute units (kg/cm²). By way of example, the authors give the results of electrometric observations conducted to evaluate the quality of an antifiltrational curtain on one of the high-mountain water reservoirs in Armenia.