Hydrocarbon production operations include water injection, varying stimulation approaches, and enhanced oil recovery techniques. These treatments often affect reservoir formation, production, and injection facilities. Such sorts of well operations cause the formation of organic and inorganic scales in the near-wellbore region and various production and injection structures. Downhole squeeze treatment is commonly used as a control measure to prevent scale precipitation. A scale inhibitor solution is introduced into a formation by applying a squeeze treatment. The method allows scale inhibitors to adsorb on the internal rock surface to avoid settling down the scale precipitates. Thus, the study of adsorption of different types of inhibitors to prevent scale formation on the reservoir rock through the execution of downhole squeeze treatment is becoming necessary. This study incorporated different experimental techniques, including dynamic adsorption experiments of chelating agents employing a coreflooding setup, inductively coupled plasma-optical emission spectrometry (ICP-OES) to inhibit the formation of iron-containing scales in limestone rocks, and ζ-potential measurements targeting determination of iron precipitation in varying pH environments on calcite minerals. The influence of the inhibitor soaking time and salt existence in the system on chelating agent adsorption was also evaluated in the coreflooding experiments. The findings based on the coreflooding tests reveal that the concentration of chelating agents plays a significant role in their adsorption on carbonate rocks. The treatments with 20 wt % ethylenediaminetetraacetic acid (EDTA) and 20 wt % diethylenetriaminepentaacetic acid produced the highest adsorption capacity in limestone rock samples by inhibiting 84 and 85% of iron(III) ions, respectively. Moreover, the presence of the salts (CaCl 2 and MgCl 2 ) considerably decreased the adsorption of 10 wt % EDTA to 56% (CaCl 2 ) and 52% (MgCl 2 ) and caused nearly 20% more permeability reduction, while more inhibitor soaking time resulted in comparably higher adsorption and lesser permeability diminution. The results of ζ-potential measurements showed that the pH environment controls iron(II) and (III) precipitation, and iron(III) starts to deposit from a low pH region, whereas iron(II) precipitates in increased pH environments in calcite minerals.
An important oilfield issue is the formation of a wide range of scales during oil and gas well operations. Oilfield scales hinder assessing an optimum hydrocarbon production as their precipitation on formation, various surface, and downhole equipment leads to many problems, including pressure decrement, formation damage, and operational failure of subsurface equipment. One type of these scales is the iron sulfide scale and based on studies in the Khuff reservoir, iron sulfide scales are likely to deposit on production tubing and rock formation. Therefore, it becomes essential to restrain the occurrence of iron sulfide scale using environmentally friendly chemicals in production tubing, water injection wells, and near-wellbore formation. The primary focus of this work is the prevention of iron sulfide scale deposition in carbonate formations during water injection applications. Iron sulfide scale inhibition was studied through dynamic inhibition adsorption experiments. In contrast to conventional experiments, for scale inhibition and adsorption of chelating agents (static bottle, dynamic filter tube tests) and simulation studies, a novel experimental setup (coreflooding experiments) was proposed to study the inhibitor adsorption. Broad concentrations of high-pH aminocarboxylic acids (such as ethylenediaminetetraacetic acid (ETDA) and diethylenetriamine pentaacetate acid (DTPA)) were examined (10 wt%, 15 wt%, and 20 wt%), at temperatures of 120°F and 200°F. Results of the study revealed that iron (III) precipitation is an obvious threat causing severe formation damage in carbonate rocks by significantly decreasing the rock permeability. Adsorption of chelating agents on limestone rocks highly depends on their concentrations. Specifically, an increase in the concentration of EDTA and DTPA at elevated temperature conditions resulted in higher adsorption. The inhibition experiments revealed that 20 wt% EDTA could significantly decrease the iron sulfide scale precipitation. Unlike the conventional testing methods for scale formation and prevention, a novel experimental setup - coreflooding during the inhibitor adsorption, formation, and inhibition of iron sulfide scale in carbonate formation was used. The main advantage of the method is the consideration of permeability alteration happening due to the scale formation. Another point is that in previous studies, various scale control chemicals and experimental approaches have been suggested for iron sulfide scale inhibition, and polymeric, phosphonate, and sulfonated co-polymeric inhibitors were used. However, the subgroup of chelating agents - aminocarboxylic acids, was used in this study.
Numerous well operations, including water injection, varying stimulation approaches, and enhanced oil recovery (EOR) techniques are implemented during the production period in order to maintain the longevity of hydrocarbon production. However, reservoir formation, production, and injection facilities are often impacted by these treatments. Well operations induce inorganic scale to form near-wellbore regions and in various production and injection structures. Consequently, the deposition of scales hinders assessing an optimum hydrocarbon production as their precipitation on formation, various surface, and downhole equipment leads to many problems, including pressure decrement, formation damage, and operational failure of subsurface equipment. As a control measure to prevent scale precipitation downhole squeeze treatment is commonly used in the petroleum industry. By applying a squeeze treatment, a scale inhibitor solution is introduced into a formation above the formation pressure, allowing the scale inhibitor to get into the deep into near-wellbore formation. Downhole squeezing allows scale inhibitors to adsorb on the internal rock surface to avoid the settling down of scale precipitates. Thus, the study of adsorption of different types of inhibitors, such as chelating agents, polymeric inhibitors, and polyphosphates on formation is becoming necessary. The study incorporated several experimental techniques, including dynamic adsorption experiments using coreflooding setup, ICP-OES (Inductively Coupled Plasma - Optical Emission Spectrometry), and ζ-potential measurements targeting evaluation of adsorption of aminopolycarboxylic acids in carbonate rocks and iron precipitation in calcite mineral. Potential precipitation of iron in varying pH environments and causing the formation of iron-containing scales was assessed through ζ-potential measurements. The findings reveal that the concentration of aminopolycarboxylic acids plays a significant role in their adsorption on carbonate rocks. The adsorption is also affected by different factors, such as the presence of salts. The results of ζ-potential measurements showed that iron (II) and iron (III) precipitation is controlled by the pH environment in calcite minerals. The treatments with 20 wt% ethylenediaminetetraacetic acid (EDTA) and diethylenetriamine pentaacetate acid (DTPA) produced the highest adsorption capacity in carbonate rock samples by inhibiting 84% and 85% of iron (III) ions, respectively. The encountered permeability damage in the adsorption tests was between 25% and 32%. Moreover, the presence of the salts considerably decreased the adsorption of EDTA and caused almost 20% more permeability reduction. Unlike the conventional testing methods for inhibitor adsorption, a novel experimental setup, coreflooding was used during the inhibitor adsorption, and scale inhibition in carbonate formation.
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