Experimental Investigation of the Interaction between a Phosphate Ester Scale Inhibitor and Carbonate Rocks for Application in Squeeze Treatments

Abstract

Studying the interaction between scale inhibitors (SIs) and chemically reactive carbonate minerals is crucial for determining SI retention in “squeeze” treatments. This study investigated the retention of the environmentally friendly SI, polyhydric alcohol phosphate ester (PAPE), on calcite and dolomite substrates. Elemental analysis of the supernatant solution as well as pH measurement and environmental scanning electron microscopy (ESEM) with energy dispersive X-ray analysis (EDX) were all used to investigate SI retention and to identify the morphology/composition of the resultant SI–Ca precipitates. Results revealed that PAPE was retained by calcite via pure adsorption at an initial test pH (pH0) of 4 and then precipitated at pH0 6. In contrast, the PAPE/dolomite system was found to be effectively pH-independent, with precipitation dominating at both pH0 values. Any temperature effect was negligible for dolomite/PAPE retention, whereas with calcite, retention was smaller at lower temperature, which is attributed to the temperature-dependence of the substrate solubility. Overall, the final pH of the system and the resulting degree of SI dissociation contributed more to PAPE retention than did the final calcium concentration. EDX analysis confirmed scale-inhibitor phosphorus in the deposited solids, indicating coupled adsorption/precipitation. This phosphorus increased with the amount of precipitation and with the temperature, confirming the corresponding static adsorption test results.

Mechanistic Investigation of Adsorption Behavior of Two Scale Inhibitors on Carbonate Formations for Application in Squeeze Treatments

“…Pure adsorption (Γ) was observed only for final scale inhibitor concentrations [SI] less than 100 ppm. For [SI] > ∼100 pm, the m/V curves in Figure deviate, indicating that coupled adsorption/precipitation (Γ/Π) behavior was occurring. ,, A very strong indicator that precipitation must be taking place is the magnitude of the apparent adsorption of DETPMP. It can be seen from Figure that on both substrates, Γ app ≈ 25 mg/g and Γ app ≈ 27 mg/g for pH 0 4 and 6, respectively.…”

“…Note that apparent adsorption is used because both adsorption (Γ) and precipitation (Π) may be occurring together, and thus the apparent adsorption is in fact a combination of both mechanisms (Γ/Π). A detailed discussion of how to analyze such experiments along with the appropriate mathematics is given in refs and . A schematic of the static adsorption and compatibility experimental procedures is shown in Figure .…”

“…Field SI squeeze treatments have been modeled quite successfully, but often the field observations are not accurate enough to distinguish clearly between different mechanistic models. A detailed analysis of a given retention mechanismfor example, pure adsorption (Γ) or coupled adsorption/precipitation (Γ/Π)requires carefully designed laboratory experiments. , The initial detailed mechanistic study of SI squeeze was conducted by Vetter, in which it was found that the “adsorption isotherms” of sand at different pH values at low temperature are almost identical, and there was a very small increase at higher pH. Sorbie et al investigated the impact of pH, temperature, and calcium on the retention of phosphonate SIs onto consolidated and crushed sandstone.…”

“…The aim of this work was to investigate the most important mechanisms governing the retention of two types of conventional SIs (DETPMP and PPCA) in limestone and calcite mineral substrates. This was achieved by carrying out a range of “apparent adsorption” experiments as described above. ,,, These apparent adsorption plots are measured in a specific fraction size of calcite or limestone (100–315 μm) at two different m/V ratios and different temperatures ( T = 80 and 95 °C). All of the SI/calcium solid precipitates were also studied using Environmental Scanning Electron Microscope/Energy-Dispersive X-ray Spectroscopy (ESEM/EDX) and Particle Size Analysis (PSA) .…”

Evaluation of Silica and Related Matrix Ion Effects on Common Scale Inhibitors

“…Mineral scale formation is one of the most significant water-related chemistry problems during energy production such as power production (cooling towers) or oil and gas operations. − It can cause billions of dollars of production loss by forming a blockage or causing the failure of equipment such as pumps or valves. , Among various mineral scales, barite is widely present and extremely difficult to control or remove. , In most cases, barite scale was formed due to the incompatible sulfate ion rich water (e.g., seawater) and barium ion rich water mixing during oilfield production. − Compared to other control methods, such as mineral scale dissolution and sulfate anion removal, the addition of chemical scale inhibitors, such as commonly used phosphonate and polymeric inhibitors, , is believed to be the most efficient and economic method to control barite scale. − These scale inhibitors are threshold inhibitors which can delay the scale formation kinetics significantly with substoichiometric concentrations . However, the inhibitor’s performances can be significantly affected by other species in the produced water.…”