Wang, Xin (Rice University) | Ko, Saebom (Rice University) | Liu, Ya (Rice University) | Lu, AlexYi-Tsung (Rice University) | Zhao, Yue (Rice University) | Harouaka, Khadouja (Rice University) | Deng, Guannan (Rice University) | Paudyal, Samridhdi (Rice University) | Dai, Chong (Rice University) | Kan, Amy T. (Rice University) | Tomson, Mason B. (Rice University)
Iron sulfide scaling is a severe problem in flow assurance and asset integrity in oil and gas and deep-water production. FeS scale control is challenging due to the extremely low solubility, fast precipitation kinetics and complexity of ferrous iron and sulfide chemistry. Despite the ubiquity of FeS, we have limited understanding about the kinetics and thermodynamics of iron sulfide. To address this problem, we have developed a reliable anoxic plug flow reactor using argon gas to remove oxygen and PIPEs or MES buffer to control pH. The FeS (mackinawite) solubility, precipitation kinetics and phase transformation were the focus of this study. The impact of temperature (25 – 90°C), pH (5.92 – 6.91), ionic strength (0.15 – 4.30 M), Fe(II) to S(-II) ratio, dispersant and chelating reagent have been investigated. It was found that mackinawite is always the first FeS precipitated and could be stable for a week. It was suggested that low pH, high temperature and low ionic strength could accelerate the FeS phase transformation. FeS precipitation is under diffusion control at pH lower than 6.1, which could be accelerated by high temperature and high ionic strength. But the precipitation kinetics would be faster at higher pH. Some evidence suggests the importance of neutral FeS(aq) species at pH 6 −7. A polymeric compound containing amide functional group showed a promising effect by controlling the FeS particle size and reducing FeS scale retention rate. EDTA showed satisfactory FeS scale inhibition effect, as well as reducing FeS scale retention and H2S corrosion rate.
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 [
Scale formation that can hinder continuous oil production is a serious problem in oilfield. Among all common scales, barite and calcite are two of the most important scales. Scale inhibitors have been widely added to prolong the induction time of scales. This study evaluates the methods and previous inhibition models to measure and predict scale formation in the presence of phosphonate and polymer inhibitors under common brine conditions. Turbidity measurement with laser light was used accurately and quickly to measure the induction time, and good reproducibility can be achieved between different sources of inhibitors. By conducting a set of independent inhibition experiments, previous models were evaluated and the demand for model improvement was carefully pointed out. On the basis of these evaluations, new ScaleSoftPizer (SSP) model was proposed by incorporating all available data under various simulated oilfield conditions (4-175 °C). The new SSP barite inhibition model was more internally consistent, and the new SSP calcite inhibition model expanded the applicable temperature ranges. The new SSP model was incorporated into SSP 2019. To prove the application of new SSP model, the predicted minimum inhibitor concentrations (MICs) were compared with lab observations and field data, which shows good consistence and improvements. This study improved the prediction of MIC over wide ranges of temperature and inhibitor types, which can significantly reduce the expenses and efforts to solve scale formation problems.
In this work a new laser-hydrothermal apparatus is designed to evaluate nucleation of scale minerals at temperature up to 250°C, its reliability is proven by measuring induction time data of barite from 90°C to 250°C at various Saturation index (SI) values, with the objective that such a design would contribute to the scale-related research at extreme temperature.
Background solution (e.g. 1m NaCl) in a borosilicate glass bottle was placed inside a hydrothermal reactor. GC oven was used for temperature control and a modified Nd-Fe-B magnetic stirrer under the oven was used for stirring. A PFA tubing was selected to be the part with contact with solution for corrosion control. Using a 0.5 ml sample loop in two separate 6-ways switch valves, Ba2+ and SO42-concentrated solutions were simultaneously injected into a background solution. After supersaturation was initiated, a laser beam penetrated through the sight glasses installed on the both sides of the reactor to record the turbidity change during the nucleation process.
Induction time (tind) of Saturation index (SI) values from 0.34 to 1.02 was measured at temperatures from 90°C to 250°C. Data correlates well with data from previous laser test at 90°C in a regular beaker experiment. The induction time (tind), that is, how fast a supersaturated solution induces nucleation and crystal growth to form detectable turbidity, decrease with temperature at a fixed SI value. For example, tind of 93 minutes at 150°C decreases to about 2 minutes at 250°C under the the same SI value of 0.65, indicating that increasing temperature facilitates the nucleation process at certain supersaturation levels. This temperature impact can be attributed both by thermodynamics and kinectic aspects.
Kan, Amy T. (Rice University) | Dai, Joey (Zhaoyi) (Rice University) | Deng, Guannan (Rice University) | Harouaka, Khadouja (Rice University) | Lu, Yi-Tseng (Rice University) | Wang, Xin (Rice University) | Zhao, Yue (Rice University) | Tomson, Mason B. (Rice University)
Numerous saturation indices and computer algorithms have been developed to determine whether, when, and where scale will form. However, scale prediction can still be challenging because the predictions from different models often differ significantly at extreme conditions. Furthermore, there is a great need to accurately interpret the partitioning of water (H2O), carbon dioxide (CO2), and hydrogen sulfide (H2S) between different phases, as well as the speciations of CO2 and H2S. This paper summarizes current developments in the equation-of-state (EOS) and Pitzer models to accurately model the partitioning of H2O, CO2, and H2S in hydrocarbon/aqueous phases and the aqueous ion activities at ultrahigh-temperature, ultrahigh-pressure, and mixed-electrolytes conditions. The equations derived from the Pitzer ion-interaction theory have been parameterized by regression of more than 10,000 experimental data from publications over the last 170-plus years using a genetic algorithm on the supercomputer DAVinCI at Rice University. With this new model, the 95% confidence intervals of the estimation errors for solution density are within 4×10–4 g/cm3. The solubility predictions of CO2 and H2S are accurate to within 4%. The saturation-index (SI) mean values for calcite (CaCO3), barite (BaSO4), gypsum (CaSO4·2H2O), anhydrite (CaSO4), and celestite (SrSO4) are accurate to within ±0.1—and for halite the values are within ±0.01—most of which are within experimental uncertainties. This model accurately defines the pH value of the production tubing at various temperature and pressure regimes and the risk of H2S exposure and corrosion. Furthermore, our model is able to predict the density of soluble chloride and sulfate SO2–4 salt solutions within ±0.1% relative error. The ability to accurately predict the density of a given solution at temperature and pressure allows one to deduce when freshwater breakthrough will occur. In addition, accurate predictions can only be reliable with accurate data input. The need to improve the accuracy of scale prediction with quality data will also be discussed.
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.
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.
Harouaka, Khadouja (Rice University) | Lu, Yi Tsung (Rice University) | Ruan, Gedeng (Rice University) | Sriyarathne, H. Dushanee (Rice University) | Li, Wei (Rice University) | Deng, Guannan (Rice University) | Zhao, Yue (Rice University) | Wang, Xin (Rice University) | Kan, Amy T (Rice University) | Tomson, Mason (Rice University)
Calcium carbonate deposition experiments were carried out by pumping a brine solution through PTFE plastic, carbon steel, and 316 stainless steel tubing at 150°C and at a maximum SICaCO3 of 1.36. The kinetics of deposition were inferred from the variation of HCO3- concentration in the effluent with changing flow rate. The inhibition kinetics were determined before, during, and after the addition of NTMP inhibitor into the system. On the metal surfaces, deposition occurred within 10 minutes of the start of the experiment and had similar behavior with changing flow rate, whereas deposition did not begin on the PTFE surface until 30 minutes had passed. No more than 1ppm of NTMP was sufficient to completely halt deposition in the PTFE and stainless steel experiments, whereas up to 2 ppm of NTMP was required in the carbon steel experiment. The deposition kinetics were indistinguishable between the metal surfaces, and were ultimately similar on the smoother hydrophobic PTFE surface once an initial coating of scale had developed. The inhibition efficiency of the NTMP was negatively affected by the corrosion products produced in the carbon steel experiments, assumed to be primarily dissolved Fe (II). Inhibitor retention was higher in the metal surfaces than in the PTFE, possibly due to the preferential adsorption of the NTMP to the surface of the Fe rich steel tubing. Our results suggest that it is the hydrodynamics of brine in the tubing, controlled by flow rate, and the SI that are the main factors controlling scale deposition. Calcium carbonate scale attachment occurs via heterogenous nucleation directly onto the surface of the tube when the brine solution approaches oversaturation from a state of equilibrium with respect to calcium carbonate. The mechanism of inhibition in our system is likely to proceed through the formation of Ca- and Fe-NTMP complexes that either poison the growth surfaces of the scale, or drop the SI of the calcium carbonate by reducing the acitivity of free Ca in the brine.
Li, Wei (Rice University) | Ruan, Gedeng (Rice University) | Bhandari, Narayan (Rice University) | Wang, Xin (Rice University) | Liu, Ya (Rice University) | Dushane, H. (Rice University) | Sriyarathne, M. (Rice University) | Harouaka, Khadouja (Rice University) | Lu, Yi-Tsung (Rice University) | Deng, Guannan (Rice University) | Zhao, Yue (Rice University) | Kan, Amy T. (Rice University) | Tomson, Mason (Rice University)
Increasing production activities in sour environments with equipment and piping made of low corrosion- resistant carbon steel result in significant iron sulfides (FeS) corrosion and scaling problems. FeS scale control is challenging as FeS formation is favored in production water chemistry (extremely low solubility and fast precipitation kinetics) with complex phase transformations. Efficient chemical control of FeS scales has not been found. A polymeric compound containing amide or its derivative functionalities showed a promising effect by controlling the FeS particle size on a nano-meter scale at threshold quantities. The FeS scales were successfully managed by forming a stable FeS particle suspension in the aqueous phase without partitioning into the oil-water interface. Current development focuses on understanding the interactions between the polymeric-compound based dispersants and environmental factors such as the presence of an oil phase, as well as silica. In addition, performance improvement of the identified dispersants by new chemical additives has been explored. Our results show that biocides such as Tetrakis (hydroxymethyl) phosphonium chloride (THPS) may not be as effective as needed for FeS scale inhibition benefit. At the tested conditions, EDTA shows satisfactory FeS scale inhibition and dissolution performance. In addition, silica significantly affects wettability of FeS particles with part of the previously oil-wet FeS partitioning into the aqueous phase. The FeS inhibition and dissolution effects of EDTA are kinetically "poisoned" by silica; while FeS-dispersing effect of polymeric compounds remains unaffected. However, the previously-shown ability that polymer dispersants keep already-formed large size FeS particles in the aqueous phase is also impaired.
Deng, Guannan (Rice University) | Kan, Amy T. (Rice University) | Dai, Zhaoyi (Rice University) | Lu, Alex Y. (Rice University) | Harouaka, Khadouja (Rice University) | Zhao, Yue (Rice University) | Wang, Xin (Rice University) | Tomson, Mason B. (Rice University)
High Ca concentration up to 40,000 mg/L in produced water was observed in Marcellus shale gas wells, such extremely high concentration have great impact to solubility of sulfate scales. To evaluate this impact, the virial coefficients for Ca-SO4 ion-interaction needs to be quantified in Pitzer equation for different P-T regimes. More solubility data with high Ca concentration at high temperature (>120°C) needs to be experimentally determined.
The solubility of anhydrite at Ca2+ concentration up to 1 m (mol/kg H2O) from temperature of 120°C to 220°C and at saturated vapor pressure was measured. A stainless-steel pressure proof reactor was designed to contain a Pyrex bottle, in which reagent grade anhydrite powder was mixed with salt solution of 0.25 m, 0.5 m, 0.77 m, and 1 m CaCl2. Sample was taken by using inner pressure to push solution through inline-filter, and then the Ca2+ and SO42- concentrations in the filtrate was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and compared over time to confirm when solubility equilibrium was reached.
Results shows that current Pitzer's equation model (ScaleSoftPitzer 2017) predicts saturation index (SI) values with an error of less than 0.1SI at up to 0.77 m Ca2+, but shows an error as much as −0.21 SI at 1 m Ca2+ condition. For typical produced water with less than 30,000 mg/L Ca (about 0.75 m), the current model gives a reliable prediction of anhydrite solubility. If the produced water contains greater than 30,000 mg/L Ca, the model may yield error that are as much as −0.2 SI. Further experiments are needed to correct the Pitzer equation coefficients for better scale predication at higher than 30,000 mg/L Ca.