The Effect of pH and Mineralogy on the Retention of Polymeric Scale Inhibitors on Carbonate Rocks for Application in Squeeze Treatments

Abstract

Summary The bulk “apparent-adsorption” behavior (Γapp vs. Cf) of two polymeric scale inhibitors (SIs), polyphosphino carboxylic acid (PPCA) and phosphorus-functionalized copolymer (PFC), onto carbonate mineral substrates has been studied for initial solution pH values of 2, 4, and 6. The two carbonate minerals used, calcite and dolomite, are much more chemically reactive than sandstone minerals (such as quartz, feldspars, and clays), which have already been studied extensively. In nearly all cases, precipitates formed at higher SI concentrations were caused by the formation of sparingly soluble SI/calcium (Ca) complexes. A systematic study has been performed on the SI/Ca precipitates formed by applying both environmental scanning electron microscopy energy-dispersive X-ray (ESEM-EDX) analysis and particle-size analysis (PSA), and this identifies the morphology and the approximate composition of the precipitates. For PPCA, at all initial solution pH values, regions of pure adsorption (Γ) (PPCA < 100 ppm) and coupled adsorption/precipitation (Γ/Π) are clearly observed for both calcite and dolomite. PFC at pH values of 4 and 6 also showed very similar behavior, with a region of pure adsorption (Γ) for PFC < 500 ppm and a region of coupled adsorption/precipitation (Γ/Π) above this level. However, the PFC/calcite case at pH = 2 showed only pure adsorption, whereas the PFC/dolomite case at pH = 2 again showed coupled adsorption/precipitation at higher PFC concentrations. For the SIs on both carbonate substrates, precipitation is the more dominant mechanism for SI retention than adsorption above a minimum concentration of approximately 100 to 500 ppm SI. The actual amount of precipitate formed varies from case to case, depending on the specific SI, the substrate (calcite/dolomite), and the initial pH (pH = 2, 4, and 6). Although the qualitative behaviors of both PPCA and PFC were similar on both carbonate substrates, the apparent adsorption of PPCA was higher on calcite than on dolomite, and the apparent adsorption of PFC was higher on dolomite than on calcite. We discuss here how these observations are related to the reactivity of the different carbonate minerals, the resulting final pH (which affects the dissociation of the SI), the Ca-SI binding, and the solubility of the resulting complex.

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

“…The two main mechanisms through which SI retention occurs in a porous medium are adsorption (Γ) and precipitation (Π). Adsorption mechanisms are thought to be influenced by an electrostatic force of attraction or van der Waals forces between inhibitor molecules and the rock surface. − These interactions are usually described by an adsorption isotherm, Γ­(C) which describes the quantity of SI retained on the mineral surface as a function of the bulk solution SI concentration, C . , The precise form of the adsorption isotherm characterizes the length and shape of the SI return curves (i.e., [SI] in the water phase vs time) after the treatment. Precipitation (denoted Π) refers to the mechanism where SI precipitates or “phase separates,” and this particulate or flocculated “precipitate” is physically retained in porous medium. ,, Precipitation squeeze treatments can give longer squeeze lifetimes than adsorption squeezes. − Although precipitation squeeze treatments appear promising for applying the SI, they may present some other issues.…”

“…However, there are an increasing number of field and laboratory studies examining these minerals, such as calcite, limestone, and dolomite, despite the challenges presented by their greater chemical reactivity. In particular, the behaviors of polymeric SIs (polyphosphino carboxylic acid (PPCA) and P-functionalized copolymer (PFC)) have been investigated previously by this group . In that system, two carbonate mineralogies (calcite and dolomite) were used as well-known representatives of carbonate formations.…”

“…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) . These techniques revealed direct information on the morphology of any precipitates formed, i.e., whether they are formed as free crystalline (or amorphous) precipitates or whether they form as “coated structures” on the surface of the calcite or limestone grains.…”

Performance of a novel green scale inhibitor

“…(3) Firstly, the critical mixing ratio of the two brines is examined to find out the maximum amount of precipitated particles at 90˚C and atmospheric pressure [21,28,29] necessary to simulate incompatible mixing process athigh-temperature standard static tests. Secondly, the critical mixing ratio test is conducted to assess the various dosage of the SI to evaluate the optimum dosage of the SI.…”

“…Secondly, the critical mixing ratio test is conducted to assess the various dosage of the SI to evaluate the optimum dosage of the SI. Finally, the impact of 10 grams [29] of dolomite and calcite rock's presence is studied to determine the SI adsorption capacity for each rock. The aforementioned simulation steps were performed with the help of PHREEQC which handles geochemical reactions at the equilibrium state.…”