| Title | Modelling of Deposition Phenomena in Low Enthalpy Geothermal Wells |
|---|---|
| Authors | Afif Abou Akar and Ioannis Ignatiadis |
| Year | 1995 |
| Conference | World Geothermal Congress |
| Keywords | geothermal well, corrosion, deposition, iron sulphide, modelling scaling, diffusion layer |
| Abstract | The well casings (most of which are of carbon steel) of geothermal plants exploiting the Dogger aquifer in the Paris Basin experience problems of corrosion and scaling related to the of the geothermal fluid and to the precipitation of iron sulphides, mainly as mackinawite A chemical code, MODEP, using a predetermined uniform corrosion rate and a simulation of scaling on the casing wall is proposed. Calculations based on mass conservation and mass balance enable us to: calculate the distribution of dissolved or degassed chemical species in the fluid as a function of temperature and pressure; (ii) calculate the saturation indexes of the fluid with respect to the various minerals; evaluate the excess of ferrous iron precipitated as mackinawite and (iv) calculate the new diameter of the casing. The basic data necessary for this model is the borehole fluid chemical composition. Two methods were used to sample the fluid: sampling with an inert bottom sampler and at the wellhead with a special composite tubing. Dissolved iron and total sulphide, measured in the production wellhead and calculated by MODEP are in a good agreement. This work continues in order to study diffusion phenomena and concentration gradients near the well wall and to improve knowledge of iron sulphide precipitation kinetics. |