Evaluation of the Reaction Kinetics of Diethylenetriaminepentaacetic


Aug 13, 2018 - Evaluation of the Reaction Kinetics of Diethylenetriaminepentaacetic Acid Chelating Agent and a Converter with Barium Sulfate (Barite) ...
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Catalysis and Kinetics

Evaluation of the Reaction Kinetics of DTPA Chelating Agent and Converter with Barium Sulfate (Barite) Using Rotating Disk Apparatus Mohamed Mahmoud, Badr Ba Geri, Khaled Abdelgawad, Muhammad Shahzad Kamal, Ibnelwaleed A. Hussein, Salaheldin Elkatatny, and Reyad Awwad Shawabkeh Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02332 • Publication Date (Web): 13 Aug 2018 Downloaded from http://pubs.acs.org on August 15, 2018

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Evaluation of the Reaction Kinetics of DTPA Chelating Agent and Converter with Barium Sulfate (Barite) Using Rotating Disk Apparatus 1,*

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Mohamed Mahmoud , Badr Ba Geri , Khaled Abdelgawad , Muhammad Shahzad Kamal , Ibnelwaleed 3 1 4 Hussein , Salaheldin Elkatatny , and Reyad Shawabkeh 1

Petroleum Engineering department, College of Petroleum Engineering and Geosciences, KFUPM, Dhahran 31261, Saudi Arabia

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Center for Integrative Petroleum Research, College of Petroleum Engineering and Geosciences, KFUPM, Dhahran 31261, Saudi Arabia

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Center of Gas Processing, College of Engineering, Qatar University, Doha, Qatar.

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Chemical Engineering Department, College of Engineering, University of Jordan, Amman, Jordan.

*Corresponding author: [email protected]

Abstract Barium Sulfate (Barite) is a major oil and gas field scale formed inside the production equipment as well as in the reservoir. During drilling of oil and gas wells, barite serves as a weighting material in different drilling fluid formulations. Barite solubility is very low in inorganic and organic acids. In this study, DTPA chelating agent and a converter (K2CO3) are introduced to dissolve barite scale. Potassium carbonate was selected as a converter because it is cheap, available, and has no environmental concerns. For the first time, the reaction kinetics of DTPA chelating agent and the converter with intact barite rock samples are investigated. Barite core samples were plugged from actual barite rock that is used to prepare the barite powder for the drilling fluid. The reaction kinetics of DTPA and the converter with barite rocks were studied by rotating disk apparatus (RDA). The results of the RDA show a linear increase in reaction rate with the disk rotational speed suggesting that mass transfer controls the dissolution of barite in DTPA chelating agent. The converter reacts with barite at high pH medium (pH above 11) and generated barium carbonate. The resulting barium carbonate added more surface area to the disk and increased the diffusion coefficient of DTPA from the bulk solution to the rock surface. Also, the complexation of barium from barium carbonate is much easier than from barite. The DTPA diffusion coefficient increased from 0.1 x 10-6 to 3.31 x 10-6 cm2/s due to the use of the K2CO3 as a converting agent. The evaluation of reaction kinetics between DTPA/converter and the rock will help design more efficient removal for both barite scale and barite filter cake in upstream oil and gas wells.

Keywords: Reaction Kinetics; Barite; DTPA Chelating Agent; Converter Scale; and Barium Carbonate.

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1.0 Introduction During drilling operation of oil and gas wells, barium sulfate (barite) is commonly used as a weighting material. Barite is favored over other weighting materials (CaCO3 and iron oxides) as it provides high-density drilling fluids with low cost 1. Barite particles causes two forms of damage during drilling oil and gas wells 2,3. Firstly, the invasion of barite particles into the porous media during the drilling process will reduce the oil and gas reservoirs nearwellbore permeability. Secondly, the formation of barite filter cake can take place that it is difficult to remove after finishing drilling operation 4,5. The barite has low solubility in water that results in deposition of barite scale in oil wells 6. Barite scale precipitation can also occur if barium from formation brine contact with the sulfate present in the injected seawater 7,8. A good understanding of barite dissolvers at various conditions is necessary owing to its growing use for oilfield applications 9,10. Several attempts were made to find a solution to dissolve barite scale and barite filter cake 9,11–17. Acids such as; hydrochloric acid (HCl), formic acid, citric acid, and lactic acid are ineffective in dissolving barite solids 16,17. Therefore, chelating agents such as diethylenetriaminepentaaceticacid (DTPA), ethylene-diaminetetraacetic acid (EDTA), and hydroxyl-ethylethylenediamine- triacetic acid (HEDTA) were introduced as alternatives to dissolve barite 13,16–18. DTPA chelating agent yielded the maximum dissolution capacity of barite 14,18. However, still, the solubility of barite particles in the chelating agent is limited (maximum is 60 wt% in DTPA)17. Due to the limited solubility of barite in DTPA, converters such as potassium and cesium carbonate were introduced to increase the reaction rate 17. Previous studies only studied the solubility of barite powder using batch reactor in chelating agents. This is the first study to report and evaluate kinetics of the reaction of intact actual barite rocks with DTPA chelating agents. The objectives of reaction kinetics study of barite with DTPA is to determine the diffusion coefficient of chelating agent to the surface of barite rocks. Diffusion coefficient is a crucial paratmeter that control the design of barite scale and barite filter cake removal in upstream oil and gas operations. The objectives of this work are; (1) to investigate the reaction kinetics of DTPA chelating agents with intact barite plugs by using rotating disk apparatus (RDA), (2) investigate the effect of adding the converter (K2CO3) on the reaction rate using RDA, and (3) combine the RDA experiments’ results with the pore size distribution and surface area analysis from the BET (Brunauer–Emmett–Teller) to understand the reaction of DTPA and converter with barite. 2.0 Rotating Disk Theory Figure 1 shows the steps of any reactive fluid with a rock surface. The reaction process involves three major steps for the reactive fluid transport from the bulk solution to the rock surface. The three steps can be summarized as follows; i. fluid transport from the bulk solution to the surface of the intact rock, ii. the reaction of the reactive fluid with the rock surface, and iii. transport of the reaction products from the surface of the rock to the bulk solution. The type of reaction regime between the reactive fluid and rock surface depends on the time each step of the three takes. The reaction is controlled by the slowest step, for example, if the fluid transport from the bulk solution to the rock surface is the slowest step, then the reaction is controlled by mass transfer. If the reaction at the surface is the slowest reaction, the reaction will be surface reaction controlled. In the mass transfer limited reactions, the fluid transport affects the reaction rate and the higher the fluid transport rate the higher will be the reaction rate. In the surface reaction limited regime, the fluid transport speed does not affect the overall reaction because the reaction takes more time at the surface of the rock.

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Figure 1—Steps of the fluid reaction with the intact rock surface. Levich (1962) and Newman (1966) performed reaction kinetics study for Newtonian fluids 19,20, the fluids used in this study are Newtonian fluids. In their studies they showed that the mass transfer rate (RMT) of the reactive fluid to the rock surface in laminar flow can be determined as follows:  

 





  C C 

(1)



 .   √ "



  . !  #.$   



(2)

In the case of mass transfer limited reaction type, the reactive fluid concentration at the rock surface (Cs) is considered to be zero. Equation 1 can be presented as follows:

 

 %  %   )* + &'( & "  %  %     .$   &' ( &'(

. .

"

,

(3)

Where: J is the mass transfer rate; A is the surface area, cm2; Cb is reactive fluid concentration in the bulk solution, M; Cs is the reactive fluid concentration at the rock surface, M; Km is the mass transfer coefficient; ω is the disk rotational speed, s-1; ρ is the reactive fluid density, g/cm3; µ is the reactive fluid viscosity, gm/(s.cm); v is the kinematic viscosity (m/r), cm2/s; Sc is Schmidt number (v/De); De is the diffusion coefficient of the reactive fluid, cm2/s. The surface reaction limited reaction regime was described by Lund et al. 21. He introduced the surface reaction rate of hydrochloric acid (HCl) with dolomite in the form of power law in which the reaction rate is a function of the reactive fluid concentration as follows: -./0  12 3  45

(4)

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Where, rHCl is the reaction rate of HCl with dolomite, moles/(s.cm2); k is the specific reaction rate, (moles /cm2.s)(mole/cm3)-n; Cs is the reactive fluid concertation at the rock surface, M; n is the reaction order. The reacting surface area of the rock can be determined by excluding the rock areosity (also called areal porosity and can be considered as volumetric porosity in homogeneous rocks). The surface area is required to determine the dissolution rate of barite from the rotating disk. The barite dissolution rate can be determined as follows:  7 89



6

75

(5)

Where; R is the barite dissolution rate, mole/(s.cm2); t is the reaction time, s; Ar is the area exposed for reaction, cm2; Ba is the barium concentration, mole; d(Ba)/dt is the slope of the straight line of the barium concentration versus time, Ar can be determined from the disk cross-sectional area (A) as follows; Ar = (1-φ)A. If the transport of the reactive fluids from the bulk solution to the barite surface is the slowest step, then the reaction will be mass-transfer limited. In this case, the disk rotational speed will affect the mass transfer rate and in turn, will affect the reaction rate. Increasing the disk rotational speed (ω) will increase the barite dissolution rate, Figure 2. The reaction regime also depends on the disk rotational speed, for example, some reactive fluids could be mass transfer limited at wide range of disk speeds and some could be mass transfer at low disk rotational speed (in which the reaction rate increases with increasing the disk rotational speed) and surface reaction limited at high disk rotational speed (reaction rate is constant and is not affected by the disk rotational speed).

Figure 2—Procedure to determine the reaction regime of DTPA chelating agent with barite.

3.0 Experiments and Materials 3.1 Materials Barium sulfate powder with average particle size of 75 microns was used for solubility experiments. Barium sulfate disks were prepared from barite rock samples for the rotating disk experiment as shown in Figure 3. The disk had a diameter and thickness of 1 inch and 0.5 inches, respectively. The surfaces of the disks were smoothened to ensure good surface reactions. 4

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The chelating agent used for this study was diethylenetriaminepentaacetic (DTPA). The structure of the DTPA is shown in Figure 4. It contains five carboxylate groups which bind to the metal center containing three N2 atoms 16,22 . The ligands form strong chelates of ratio 1:1 in high pH solutions. Though DTPA could be sodium or potassium based, our previous study shows that barite has high solubility in potassium-based DTPA 17. Thus, KOH was used to prepare the solution for this study. In high pH medium, DTPA is deprotonated with time and its affinity for barium ion increases. Thus, DTPA solutions were kept at a pH above 12 for it to reach maximum chelation capacity. This happens when ligands are totally deprotonated (Y-5). The distribution of DTPA chelating agent as a function of pH can be presented as HmYm−n, where n is the number of carboxylic groups, and m is the number of acidic protons. In this study, we used fully deprotonated DTPA (Y-5), in which m = 0 and n = 5, DTPA has five carboxylic groups and zero protons at pH greater than 11.

Figure 3—Barite disks for rotating disk experiments.

Figure 4—DTPA structure.

3.2 Materials Characterization Elemental analysis of the treated and untreated barite sample was conducted using Energy Dispersive X-ray spectroscopy (EDX). SEM images were obtained before and after dissolution in chelating agent to estimate the surface characteristics of barite particles. The barite samples were dried for six hrs and gold-coated before taking the images. The mineralogy of industrial barite was determined by X-ray diffraction spectroscopy (XRD). Moreover, it was used to determine the mineral composition of solids precipitated after the solubility test. ASAP 2020 Micromeritics equipment was used to determine the pore size distribution and surface area of the rock cuttings. Untreated and DTPA-treated barite powder samples were evaluated. Degassing of 0.4 g of barite powder was done for 3 hrs at 300 °C to remove volatile and humid components. Nitrogen adsorption tests at 77 K were performed afterward. Adsorption/desorption curves, pore size, and surface area of the samples were determined by the Barret- JoynerHalenda (BJH) Analysis method.

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Fourier transform infrared (FTIR) analysis spectrophotometer from Perkin Elmer was used to determine the functional groups in the treated and untreated barite samples. A pellet composed of barite and potassium bromide (KBr) was prepared and then analyzed. The wave number of the instrument ranged from 400-4000 cm-1. 3.3 Solubility Experiments Solubility experiments were performed using fixed solid/liquid ratio (4 g of solid barite/0.1 L DTPA). This ratio was selected based on the thickness of barite scale and the wellbore diameter in upstream oil and gas wells 23. DTPA concentrations for the test ranged from 10-40 wt % to determine the optimum concentration for maximum barite dissolution. The experiments were performed at 200 °F for 24 hours. The RDA was used to determine the dissolution and reaction rates of DTPA and DTPA +K2CO3 with barite rock samples. RDA consists of reaction cell, reservoir cell to store the fluid, and auto sampler for sample collection at a constant time interval (Figure 5). The reaction experiments were carried out at 250oF and 1000 psi. The barite rock sample disk was attached to the reactor using heat shrinkage tube that covers all sides except the surface of the sample that is exposed to reaction with the fluid in the reactor. The concentration of DTPA in all experiments was 20 wt% at pH 12 (optimum concentration). The experiments were carried out using varying disk speeds (500-2000 rpm).

Figure 5—The RDA apparatus used in this study.

4.0 Results and Discussion 4.1 Barite Rock Characterization Analysis Elemental analysis was conducted using EDX spectroscopy to estimate the composition of Barite. Figure 6 confirmed the presence of major impurities i.e. Si, Al, K, Ca and Fe in the studied sample with a concentration range between 5% to 7%. Moreover, peaks appeared at 4.46 keV and 2.31 keV were attributed to Ba and S, respectively. On the other hand, the composition of Ba, S, O and impurities were 57.4 wt%, 11.9 wt%, 25 wt% and 5.8 wt%, respectively. The EDX results shows that the purity of the barite was approximately 94 %. However, the peaks appeared in the XRD analysis at 20.46 2; (011), 22.79 2; (111), 24.87 2; (002), 25.86 2; (210), 26.85 2; (102), 28.75 2; (211), 31.53 2; (112), 32.81 2; (020), 42.59 2; (113) and 42.93 2; (122) shows that the barite purity was > 99wt% with some unknown peaks representing impurities. According to SEM analysis, the length of the pore of barite was 2-3µ and the width was 1-2µ. 6

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Figure 6—SEM and EDX analysis of the untreated barite.

4.2 Barite Solubility Results The solubility of the barite was evaluated using different concentrations of potassium DTPA (DTPA-K5). Figure 7 shows that the optimum DTPA concentration is 20 wt% at which barite solubility reached the maximum value (67 wt% and 27 g/L). Sodium DTPA was investigated as well at different concentrations and it shows an optimum concentration of 20 wt% and the maximum barite solubility was 38 wt% (15 g/L). Therefore, in this study, potassium based DTPA was used for further investigation. A similar set of experiments was conducted by adding potassium carbonate (converter) at different concentrations to the 20 wt% DTPA-K5 at 200oF for 24 hrs. The optimum concentration of potassium carbonate was 6 wt% at which the barite solubility increased from 67 wt% to 95 wt% after 24 hrs. The optimum potassium carbonate concentration was determined at the same conditions (pH =12, 200oF, and 20 wt% K5DTPA for 24 hours). Figure 8 shows that the optimum converter (potassium carbonate) concentration is 6 wt% which yielded the maximum barite solubility. Barite solubility increased from 68 wt% at zero converter concentration to 85 wt% at 6 wt% converter concentration.

Figure 7—The solubility of barite at different concentration of DTPA-K5 after 24 hrs (pH =12), T=200 °F). 7

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Figure 8—Barite solubility at different converter concentrations in 20 wt% DTPA after 24 hrs (pH =12), T=200 °F).

4.3 Barite Conversion to Barium Carbonate Using Potassium Carbonate Figure 9 shows the mechanism of potassium carbonate which acts as a converter. This set of experiments was conducted at 200o F using potassium hydroxide solution to buffer the pH to 12. The conversion takes place according to the following equation: B.C

 2 [email protected]