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 [
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.