Elemental analysis of scale inhibitors' effect on water incompatibility in carbonate reservoirs: Modeling, bulk and core scales studies

Abstract

Water flooding is one of the common techniques for increasing petroleum reservoirs' pressure and production life. Seawater (SW) is a preferable choice for waterflooding because of its high availability and low cost. However, SW could be incompatible with formation water (FW) and causes to precipitate inorganic minerals and reduce reservoirs' permeability. A method for preventing inorganic scales is using scale inhibitors (SIs) which need more precise studies to find the critical factors for achieving better efficiency. In this study, the effect of Hydroxyethylenediphosphonic Acid (HEDP) and 2-Phosphonobutane −1,2,4-Tricarboxylic Acid (PBTC) on preventing inorganic scales formation were studied in three stages. In the modeling step, mixing FW and SW was simulated by PHREEQC software. In the second step, as static experiments, the inhibitor efficiency (IE) of two SIs were compared. At dynamic experiments, the performance of SIs in carbonate rocks was studied by core flooding tests. ICP analyses were taken on solutions for interpreting results measured in both static and dynamic scenarios. Results indicated that the ionic composition of SW and FW plays a vital role in types of inorganic scales deposition. PHREEQC software could predict type and amount of scales although its prediction is 9% more than experimental results. It was shown that although SIs could mitigate precipitating inorganic minerals, they have different performances in each concentration. While HEDP is more effective in lower concentrations, PBTC's efficiency will improve with rising its concentration. Elemental analysis showed 100 ppm HEDP has %65 IE which is the most efficient SI. The results of dynamic experiments demonstrated that HEDP and PBTC have a pleasing inhibitory effect in carbonate rocks. The presence of SIs in SW could decrease formation damage during flooding into carbonate reservoirs. • Scale inhibitors' effects were studied in modeling, bulk and core flooding steps. • Elemental Analyses were used to study the scale inhibitors' mechanisms. • Scale inhibitors have not the same efficiency in different concentrations. • HEDP at lower and PBTC at higher concentrations are more effective. • PBTC and HEDP have a pleasing performance in carbonate reservoirs.