Experimental Studies of Rock-Water Interactions Occuring During the Circulation of a Geothermal Doublet in a Carbonate Environment

Abstract

We presented in the Brussels Seminar (1) (December 1977), the results of a theoritical study on chemical reactions occuring in the exploitation of a geothermal doublet.

The conclusions in the case of the MELUN geothermal exploitation (Paris Basin) were as follows:

• At the production the water is a little supersaturated related to calcite.

• After the thermals exchanges water become agressive, till the rein jection occurs in the reservoir.

• The fresh reinjected water dissolves the reservoir up to the saturation with calcite.

• The water goes through a thermal front (2) and the rewarming causes super saturation versus calcite.

The present study,essentialy experimental, concerns the relations between flow and chemistry, the evolution of the reservoir, and the consequence on the life time of the doublet.

First, the experimental results permit to reach the speed of calcite dissolution and to show in the case of MELUN doublet that dissolution take place in a very short time after the reinjection. The volume of the reservoir influenced, depends on the heterogeneity of this one. The precipitation, wich is only a function of temperature variation, take place at the thermal front, in all the reservoir, during the life of the doublet. Dissolution open heterogeneity, precipitation has not a great effet on reservoir permeability.

An simplificated simulation model, shows that this physicochemicals phenomena have no results on the life time of a doublet located in a calcareous reservoir.