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Lu, Alex Yi-Tsung (Impac Exploration Services Rice University) | Paudyal, Samridhdi (Rice University) | Ko, Saebom (Rice University) | Dai, Chong (Rice University) | Ouyang, Bingjei (Rice University) | Deng, Guannan (Rice University) | Zhao, Yue (Rice University) | Wang, Xing (Rice University) | Mateen, Sana (Rice University) | Liu, Helen (Rice University) | Yo, Tina (Rice University) | Kan, Amy (Rice University) | Tomson, Mason (Rice University)
Barium sulfate is one of the most serious problem in mineral scale precipitation, the deposition of barite on the surface is a concern to flow assurance in the oil well. The scale formation is typically predicted by thermodynamic solubility limit. However, it is believed that a kinetically stable region exists where no scale will form even when the solution is supersaturated. The purpose of this study is to identify the existence of such a supersaturated region where scale does not form and to determine whether inhibitor is needed to control scale at this range of supersaturation.
Series of experiments were conducted in both batch reactor and flowing tube to investigate the range of supersaturation index (SI) where barite forms. In the batch experiments, a green laser apparatus was used to determine the induction time, which is defined as the time elapsed between the creation of supersaturation and detectable particle formation. In the flowing tubing experiments, the barium sulfate solution was continuously injected into a 92.7 cm 316 stainless steel tubing with 0.21 inch ID at SI = 0.3 to 1.2 at 120°C. The traveling time inside the tubing is 5 minutes with flow rate = 240 ml/hr. When barite SI = 0.3, no deposited barite were found in flowing tube which agrees with measured induction time in batch. However, at barite SI = 0.5 to 0.9, the deposited crystals were observed even though the predicted induction time is much longer than 5 minutes in the reactor tubing. The contradiction is, the barite deposited inside the flowing tube even though it was predicted not to precipitate in such short time according to batch experiment results. –The objective of this study is to resolve this apparent contradiction.
The presence of the hydrodynamic boundary layer may explain this phenomena. Further investigations were conducted in a microfluidic device to visually measure the time and size of deposited crystals to verify the hypothesis. The measured nucleation time corresponds with the batch reactor nucleation time. The results indicate that the supersaturated solution inside the boundary layer may have enough time to precipitate and deposit. This concept explains some of the field experience that the scaling happens even at a low SI value.
Furthermore, 0.25 ppm DTPMP can inhibit most of the barite deposition for 48 hours at 120°C with barite SI = 0.9. The result indicates that with trace amount of inhibitors in the boundary layer, the barite deposition can be prevented. On the other hand, 0.25 ppm PPCA shows partial inhibition and 1.0 ppm PPCA can completely inhibit barite deposition for 48 hours at 120 °C when barite SI equals to 0.9.
This work contributes to the verification of the kinetic stable SI range. The experimental results suggest that the deposition can take place inside the boundary layer even at a SI value predicted to be safe. Trace amounts of inhibitors can prevent the deposition at the same conditions. It is believed that these results provide a novel view of scaling risk prediction.
Wang, Xin (Rice University - Brine Chemistry Consortium) | Ko, Saebom (Rice University - Brine Chemistry Consortium) | Lu, Alex Yi-Tsung (Rice University - Brine Chemistry Consortium) | Deng, Guannan (Rice University - Brine Chemistry Consortium) | Zhao, Yue (Rice University - Brine Chemistry Consortium) | Dai, Chong (Rice University - Brine Chemistry Consortium) | Paudyal, Samridhdi (Rice University - Brine Chemistry Consortium) | Kan, Amy T. (Rice University - Brine Chemistry Consortium) | Tomson, Mason B. (Rice University - Brine Chemistry Consortium)
In this study, a plug flow reactor was built to investigate iron sulfide scale precipitation at various temperatures, pH and ionic strength conditions and two pieces of carbon steel C1018 coupons were put inside as reaction surfaces. The ferrous ion and total sulfide in collected effluent samples were measured to determine precipitation kinetics and solubility. The solid that formed on the steel surfaces were analyzed by Scanning Electron Microscopy (SEM/EDS) and X-ray Diffraction (XRD). The solubility data from this study and literature were collected and fitted by Matlab to build up a reliable FeS solubility prediction model. The experimental results show that mackinawite is the predominant precipitated scale and could be stable for a week at pH higher than 6.0. Iron sulfide precipitation is under diffusion control, accelerated by high temperature and ionic strength. At pH 6–7, the aqueous phase neutral species, such as
As the drilling and exploitation in oil and gas production industry become more aggressive, iron sulfide (FeS) corrosion and scaling problems are more frequently encountered [1,2]. In sour environment, hydrogen sulfide (H2S) is a natural constituent of reservoirs or generated by sulfide reducing bacteria. Since the low corrosion resistant steels are widely used in many production equipment like piping and separation system, the presence of H2S could lead to weight loss corrosion or sulfide stress cracking (SSC) . Meanwhile, free ferrous ions (Fe(II)) could be released due to corrosion, dissolution of iron rich mineral or production stimulation activities such as acidification , resulting in FeS scaling issues. Iron sulfide (FeS), as the primary product of H2S corrosion and precipitation, has already been a severe concern in oil and gas industry for proper design of corrosion prevention and safe production. In order to develop better tools for iron sulfide control, it is imperative to build up a reliable prediction model for iron sulfide solubility in mixed brine solutions over a wide range of conditions.
Zhao, Yue (Rice University) | M. Sriyarathne, H. Dushanee (Rice University) | Harouaka, Khadouja (Rice University) | Paudyal, Samridhdi (Rice University) | Ko, Saebom (Rice University) | Dai, Chong (Rice University) | Lu, Alex Yi-Tsung (Rice University) | Deng, Guannan (Rice University) | Wang, Xin (Rice University) | Kan, Amy T (Rice University) | Tomson, Mason (Rice University)
Silica is ubiquitous in oil and gas production water because of quartz and clay dissolution from rock formations. Furthermore, the produced water from unconventional production often contains high Ca2+, Mg2+ and Fe2+ concentrations. These common cations, especially iron, can form aqueous or surface complexes with silica and affect the nucleation inhibition of other scales such as barite. Thus, it is important to investigate the silica matrix ion effects on barite scale inhibitors efficiency to evaluate inhibitor compatibility with silica and common cations in produced waters.
In this study, experimental conditions were varied from 50 mg/L to 160 mg/L SiO2 in the presence of Ca2+ (1,000 and 16,000 mg/L), Mg2+ (2,000 mg/L) and Fe2+ (10 mg/L) at 70°C and neutral pH conditions, all with a background of 1 M NaCl. Our laser scattering apparatus was used to study the effect of silica matrix ions on barite nucleation inhibition [
This paper discusses research on performance of scale inhibitors in the presence of ferrous ion. Iron ion is the most abundant heavy metal ion in wastewater and oilfield produced water. Fe(II) is the dominant form of iron ion in oil and gas wells due to the downhole high anoxic conditions. Fe(II) can form FeS and FeCO3 which will cause severe problems in production. Further, it is important to thoroughly investigate the inhibitor compatibility with these cations in oilfield as the existence of iron in solution effects on inhibitor chemistry.
In this research, Fe(II) effect on various scale inhibitors on barite was tested using an improved anoxic testing apparatus along with laser light scattering nucleation detection method. In this newly designed apparatus strict maintenance of anoxic condition is guaranteed by constant argon flow and switch valve to transfer solution. Moreover, the high Fe(II) tolerance concentration for common inhibitors were tested by varying Fe(II) concentrations from 50-100 mg/L at 90°C and near neutral pH conditions. Most scale inhibitors show good Fe(II) tolerance at experimental conditions, while the inhibition performance of phosphonates were significantly impaired by Fe(II). It is proposed that the formation of insoluble precipitates between Fe(II) and phosphonate is very likely the reason behind the observed significant impairment. Further, two methods to reverse the detrimental effect of Fe(II) on barite scale inhibitor performance is investigated and discussed here. First, a most common organic chelating agents used in oilfield, EDTA, was tested for its ability to reverse the detrimental effect of Fe(II) on scale. Secondly, Fe(II)/Inhibitor concentration ratio was changed so that remaining inhibitor in the aqueous phase would conduct the scale inhibition.
Lu, Alex Yi-Tsung (Rice University) | Ruan, Gedeng (Rice University) | Harouaka, Khadouja (Rice University) | Sriyarathne, Dushanee (Rice University) | Li, Wei (Rice University) | Deng, Guannan (Rice University) | Zhao, Yue (Rice University) | Wang, Xing (Rice University) | Kan, Amy (Rice University) | Tomson, Mason (Rice University)
Deposition of inorganic scale has always been a common problem in oilfield pipes, especially in raising safety risk and producing cost. However, the fundamentals of deposition mechanism and the effect of various surface, temperature, flow rate and inhibitors on deposition rate has not been systematically studied. The objective of this research is to reveal the process of barium sulfate deposition on stainless steel surfaces.
In this work a novel continuous flow apparatus has been set up to enable further investigation of deposition rate, crystal size and morphology and the effect of scale inhibitor. In this apparatus supersaturate barium sulfate solution is mixed and passed through a 3 feet stainless steel tubing with ID = 0.04 inch or 0.21 inch at 70 to 120 degree C. The barium concentration is measured at the effluent to quantify the concentration drop. After 1 to 200 hours the tubing is cut into pieces to measure the barite deposition amount and observe the barite crystal morphology using SEM.
Under the experimental conditions, the deposition rate along the stainless steel tubing can be modelled by second order crystal growth kinetics, the SEM micrograph also shows that most of deposited barite is micrometer sized crystals. The highest deposition rate happens at the beginning of the tubing even before the expected induction time of bariums sulfate. The results indicated that the deposition happens even before the mixed solution is expected to form particles, which suggest that the heterogeneous nucleation might be the dominate mechanism in the initial stage, then crystal growth takes place and governs the deposition.
The mechanism of scale attachment to tubing surface has never been well-understood. The apparatus in this work provides a reliable and reproducible method to investigate barium sulfate deposition. The findings in this research will enhance our knowledge of mineral scale deposition process, and aid the use of inhibitors in mineral scale control.