Technical Committee Reservoir Engineering

Correct determination and forecast of the conductivity of reservoir water under in situ conditions

The main aim of the project was to determine the correct conductivity of synthetic brines under reservoir conditions. A novel high pressure conductivity cell was used, which allows highly resolved measurements without elongated time consumption for replacement of solutions and setting of thermal equilibrium. According to the salinity prevailing in German reservoirs, the test series were related to a concentration range > 1 val•L⁻¹.

The report comprises series of measurements on NaCl/CaCl₂- and NaCl/MgCl₂-solutions in the temperature range from 25 to 150 °C and pressure range from 2 to 70 MPa. Additionally, the conductivity of brines and formate containing drilling mud's were determined in the range from 2 to 40 MPa and from 25 to 150 °C.

A numerical model was developed successfully on the basis of the DEBYE-HÜCKEL-ONSAGER equation including ion association and macroscopic fluid behaviour. Related to the concentration range c > 1,5 va1•L⁻¹, valid for German reservoirs, the regression resulted in standard errors of 0.3 % for a temperature range of 60 ≤ t ≤ 150 °C using the experimental data extrapolated to p → 0. < t 0 extrapolated experimental data one standard deviation < 0.3%.