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.
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.
Zhang, Nan (Statoil) | Schmidt, Darren (Statoil) | Choi, Wanjoo (Statoil) | Sundararajan, Desikan (Statoil) | Reisenauer, Zach (Statoil) | Freeman, Jack (Statoil) | Kristensen, Eivind Lie (Statoil) | Dai, Zhaoyi (Rice University) | Kan, Amy (Rice University) | Tomson, Mason (Rice University)
Produced water from the Bakken and Three Forks formations in the Williston Basin is notably high in total dissolved solids, which leads to many well maintenance issues related to halite scaling (salt precipitation). Fresh water is widely used to prevent halite scaling; however, initial treatment programs tend to "overtreat" the problem and leads to high operation and maintenance costs. An effort to improve halite scale management has been explored, which includes identification of wells that need fresh water injection; optimization of the fresh water volumes; minimizing deferred oil production; and preventing other scales associated with the presence of fresh water in the wellbore. Several methodologies have been applied to characterize halite scaling and achieve optimization of fresh water treatments. A scaling prediction model was developed and validated with literature data and field data. The model calculates saturation ratios and optimal fresh water volume, which provides critical inputs for treatment recommendations. Field tests have been conducted to dynamically characterize produced fluids. Results have influenced new methods for treatment and fresh water injection techniques. Halite scale inhibitors have also been examined in laboratory and field tests. This work resulted in optimizing both fresh water and chemical treatment programs to minimize halite scaling. Significant cost savings have been achieved from reduced fresh water usage, thereby lowered produced water disposal.
Yan, Fei (Rice University) | Zhang, Fangfu (Rice University) | Bhandari, Narayan (Rice University) | Ruan, Gedeng (Rice University) | Alsaiari, Hamad (Rice University) | Dai, Zhaoyi (Rice University) | Liu, Ya (Rice University) | Zhang, Zhang (Rice University) | Lu, Yi-Tsung (Rice University) | Deng, Guannan (Rice University) | Kan, Amy (Rice University) | Tomson, Mason (Rice University)
Turbulent flow in oilfield pipes is very common, especially around chokes, tubing joints, and safety values. However, the effect of turbulence on mineral scale precipitation has not been well understood. The objective of this study was to investigate mineral scale formation and inhibition under turbulent conditions.
A novel tubing testing method has been developed to enable the study of turbulence in a tubing apparatus. In the tubing apparatus that consists of a long tubing (200 to 500 ft) and a high flow pump, high-velocity turbulent flow was generated. In another tubing experiment, a valve was installed in the tubing to examine the impact of valves on mineral scale precipitation. Barite scale formation and inhibition by inhibitors were investigated in turbulent flows by these novel approaches.
In the experiment, barium concentrations in the effluent of the tubing were measured to determine whether barite precipitation occurred in the tubing. Critical saturation index (SI) was determined by a series of experiments for both laminar and turbulent flow. Experimental results show the effect of turbulence depends on several factors such as reactant ratio and scale inhibitor. Under our test conditions, when the molar ratio of sulfate to barium is around one, we observe no difference in barite precipitation kinetics between laminar and turbulent flow without scale inhibitor; however, in the presence of scale inhibitor, barite precipitation kinetics is slightly faster in turbulent flow, or critical SI is higher in laminar flow than that in turbulent flow. When the molar ratio of sulfate to barium is high, critical SI of laminar flow is always slightly higher than turbulent flow with and without inhibitor. Two different tubing materials, i.e. polyethylene and stainless tubing, were both investigated in this study and experimental results shows the effect of turbulence on barite precipitation kinetics is the same for both materials. In the tubing with valve experiment, the valve in the tubing did not show an influence on barite precipitation kinetics.
This paper presents a novel tubing apparatus to investigate the effect of turbulence on scale control in oilfield. The findings in this paper will advance our understanding in scale control especially under turbulent conditions, and aid in developing optimal doses of scale inhibitors with regard to flow regimes.
Dai, Zhaoyi (Rice University) | Zhang, Fangfu (Rice University) | Yan, Fei (Rice University) | Bhandari, Narayan (Rice University) | Ruan, Gedeng (Rice University) | Zhang, Zhang (Rice University) | Liu, Ya (Rice University) | Alsaiari, Hamad A. (Rice University) | Lu, Yi-Tsung (Rice University) | Deng, Guannan (Rice University) | Kan, Amy T. (Rice University) | Tomson, Mason (Rice University)
Mineral scale formation can lead to the blockage and shutdown of production wells in the oil and gas industry. Large amounts of scale inhibitors are added to mitigate the losses due such mineral scale formation. Both insufficient and excessive scale inhibitor additions can cause unnecessary expenses. Because inhibition mechanisms are poorly understood, current models do not predict accurately the minimum effective dosage (MED) required for different inhibitors, temperatures, and inhibition times over wide ranges. Using a new approach, this paper developed a theoretical model to predict scale inhibition kinetics based on the classical nucleation theory and the regular solution theory. This model assumes that scale inhibitors can change the nucleus structure and the apparent saturation status of the scale minerals. These impacts were modeled to be proportional to the inhibitor concentrations. The model accurately predicted the precipitation and inhibition kinetics of barite and calcite with or without the presence of eight different scale inhibitors up to 90 and 175°C, respectively. This study can be used as a template to evaluate scale and inhibition kinetics, predict MED, and elucidate scale inhibition mechanisms on a common theoretical basis.
Yan, Fei (Rice University) | Bhandari, Narayan (Rice University) | Zhang, Fangfu (Rice University) | Ruan, Gedeng (Rice University) | Dai, Zhaoyi (Rice University) | Liu, Ya (Rice University) | Zhang, Zhang (Rice University) | Alsaiari, Hamad (Rice University) | Kan, Amy (Rice University) | Tomson, Mason (Rice University)
Static jar test and dynamic loop are two major test methods used for study of mineral scale formation and evaluation of scale inhibitors. In both methods, the flow is generally in the regime of laminar condition, which may not be representative of turbulent flow under field conditions. Turbulent flow in oilfield pipes is very common, especially around chokes, tubing joints, and safety values. The objective of this study is to investigate mineral scale formation and control under turbulent conditions.
A novel testing method of rotating cylinder apparatus has been developed for turbulent conditions. In rotating cylinder experiments, highly turbulent flow (up to a Reynolds number of 11,000) was created by a rotating cylinder under field temperature of 70 °C. Barite scale formation and inhibition by several typical inhibitors were investigated under different flow conditions.
During the experiments, barium concentration was measured periodically to determine scale kinetics. Barite precipitate was collected at the end of the experiment and examined by scanning electron microscope (SEM). Experimental results show no significant difference in precipitation kinetics between laminar and turbulent flow without scale inhibitors. However in the presence of scale inhibitors, precipitation kinetics was slower under high turbulence. SEM images also display major difference in barite size and morphology between different flow conditions. Highly crystalline barite with an average size of 10 µm was found in laminar flow, whereas amorphous or poorly crystalline barite of only sub micrometers was formed in turbulent flow. These results indicate that scale inhibitors may be more effective under some turbulent conditions, as opposed to previous observations.
The insights presented in this work will help to understand scale control in oilfield pipes especially under turbulent conditions, and develop optimal doses of scale inhibitors with regard to flow regimes.