Incompatibility of Injection Water with Formation Waters from Different Depths

Abstract

This paper aims to evaluate the damage that might occur as a result of incompatibility between 
injection and reservoir waters under reservoir and surface conditions. The amount of scale formed was 
determined at surface and reservoir conditions and different mixing ratios for five produced water samples 
which have been collected from locations DD and EE and tested for parameters of (Temperature, pH, O2, 
CO2 and H2S) at site and metal content of these water samples (i.e. A, B, C, D, E and produced water) as 
shown in Table (1). Five water samples (i.e. A, B, C, D, E and produced water) have been tested for waterwater compatibility test with different mixing ratios at surface and reservoir temperatures. Each mixture 
was kept for twenty four hours at desired temperature. The mixtures were filtered through cellulose nitrate 
filter paper with pore size of 0.45μm. The formed precipitates were collected, dried at 95 ºC and weighed to 
calculate the amount of deposits. The filtrates were immediately analyzed by Inductively Coupled Plasma 
(ICP) to determine the cations such as (Ca2+, Sr2+, Ba2+ and total Fe) that might react with anions (i.e. 
SO4
2-, CO3
2- and HCO3
-
) to form mineral scale. These tests demonstrated that CaCO3 and SrSO4 could be 
precipitated in different amounts depending on mixing ratios and conditions of temperature and pressure. 
Also, the scale predications have been performed using Multiscale software (7.1) to predict the tendency of 
scale formation and to compare that with the laboratory work which includes mixing of injection water with 
formation waters from different depths at surface and reservoir conditions of temperatures & pressures. This 
prediction covers the type, extent and location of all scale depositions that are expected to form during water 
injection period. Tests were conducted to identify the main scaling compounds when produced water mixed 
with the formation water. The basis of positive evidence of scaling encountered in the laboratory tests, a 
computer simulation program has been carried out to support the incompatibility of these brines when mixed 
at desired conditions.