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Collaborating Authors
Drilling Fluids and Materials
Evaluation of Hydrogen Sulfide Scavengers for Use with Static Mixers
Lehmann, Marc (INPEX Australia Pty Ltd) | Pojtanabuntoeng, Thunyaluk (Curtin Corrosion Centre Western Australia School of Mines: Minerals, Energy and Chemical Engineering, Curtin University) | Long, Yu (Curtin Corrosion Centre Western Australia School of Mines: Minerals, Energy and Chemical Engineering, Curtin University) | Yookhong, Marisa (Curtin Corrosion Centre Western Australia School of Mines: Minerals, Energy and Chemical Engineering, Curtin University) | Iannuzzi, Mariano (Curtin Corrosion Centre Western Australia School of Mines: Minerals, Energy and Chemical Engineering, Curtin University)
Abstract The efficiency of hydrogen sulfide scavengers directly injected into gas streams is often compromised by short contact times due to space limitations on offshore assets. The use of static mixers is often employed to increase the efficiency of gas-liquid mixing. The performance of two commercially available hydrogen scavenger products were assessed in the laboratory utilising a specially fabricated test chamber designed to mimic a static mixer. A continuous feed of both gas and a liquid scavenger solution were mixed through a glass bead static mixer. The liquid scavenger was atomized into the gas prior to traveling through the bed. The impact of dose rate, water content, carbon dioxide and contact time were assessed on the scavenging efficiency and kinetics of two triazine chemicals used to sequester H2S from a gas stream containing 180 ppmv H2S in nitrogen, to achieve a target H2S concentrations of <10 ppmv. Efficiencies derived from the test apparatus revealed that the formulation based on the ethanolamine triazine chemistry performed significantly better than the methylamine triazine product at the two contact times of 3 and 25 seconds. The equilibration time required to reach the target concentration were significantly longer at the shorter contact time, and unachievable without the static mixer. The dosages of scavenger required to reduce the H2S concentrations from 180 ppmv to 10 ppmv were much higher than theoretical dosages. The addition of water to the scavenger mixtures was found to increase the efficiency of the ethanolamine scavenger but decrease the performance of the methylamine based triazine. The importance of atomisation of the scavenger onto the fixed bed was reinforced by the dramatic reductions in performance associated with a lack of atomisation. The presence of CO2 had no significant impact on the scavenging efficiency but had a kinetic impact and reduced the time to achieve the target concentration.
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Well Drilling > Drilling Fluids and Materials (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Health, Safety, Environment & Sustainability > Health > Noise, chemicals, and other workplace hazards (1.00)
Abstract Underbalanced drilling technology is widely used to minimize formation damage in the reservoir section and enhance productivity. It involves drilling with a fluid whose hydrostatic pressure is lower than that of the formation being drilled. As a consequence of this lower hydrostatic there is a continuous flow of hydrocarbons to surface which is handled by separation equipment and exported thru pipelines where they exist or burned at the flare if no transportation infrastructure is located near rig-site. The injection of nitrogen into drill-pipe to lighten the hydrostatic pressure of the drilling fluid introduces significant challenges with regards to corrosion mitigation planning. A very well developed corrosion mitigation plan often exists for single phase drilling fluid but the introduction of a gaseous phase leads to changes that need to be incorporated to prevent against excessive corrosion. Problems and complications due to corrosion issues were hindering an underbalance drilling operation's progress. This paper examines how, optimizing the corrosion control techniques leads to improved drilling performance in subsequent bit runs. The willingness by the operator to tweak and improve the chemical concentrations and learn and apply those lessons learned immediately in the field pays immediate dividends.
- North America > United States (0.28)
- Asia > Middle East (0.28)
- Well Drilling > Pressure Management > Underbalanced drilling (1.00)
- Well Drilling > Drilling Operations (1.00)
- Well Drilling > Drilling Fluids and Materials (1.00)
- Well Drilling > Drilling Equipment (1.00)
Abstract New compounds have demonstrated effective scavenging of hydrogen sulfide with potential for preventing deposition of metal sulfides. These compounds come from a variety of functional families and compete against typical scavenging technology well with respect to molar efficiency, reaction rate, and stability. These inhibitors not only work on existing sulfide but some can also be modified to change the oxidation state of the system to provide a non-scaling scenario. The presence of hydrogen sulfide is an ever increasing problem in the oilfield, whether the origin is biological or formation dependant. The presence of extremely toxic hydrogen sulfide increases the corrosion rates of many metals and makes necessary the sweetening of produced hydrocarbon. If solubilized metals such as iron, lead or zinc are present in the fluid, the deposition of sulfides may occur as flow restrictive scale on the tubulars, leading to corrosion and/or biofilm augmentation or formation damaging fine particulate in the pay zone. These single component inhibitors were tested in standard synthetic formation waters which were either sulfide laden and/or metal or sulfide laden. Waters derived were standard unadulterated species at various pHs or were acidified and then spent on carbonate. The rate of sulfide uptake was monitored and the soluble metal ions were determined. Response surfaces were generated for a few key inhibitors and the performance of the inhibitors was compared to standard inhibitors. Stability was also checked to ensure insoluble or reversible scavenging species were measured. The use of these scavengers for drilling, stimulation, completion, and produced fluids provides the service company and/or operator with a viable treatment for problems incurred when treating sour reservoirs.
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Reservoir Description and Dynamics (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene (1.00)
- (2 more...)
Abstract The Karachaganak Field, which was discovered in 1979, is located in north-west Kazakhstan on the northern margin of the Pre-Caspian Basin. Production from this field contains 4 - 4..5% H2S. The Kashagan field, located offshore in the North West part of the Caspian Sea, averages 10-12% H2S concentration. An environmentally friendly H2S scavenger has been used in the Caspian area since 2006 in the invert emulsion drilling fluid systems. The operators had a standard practice of maintaining an excess of lime (2.5 kg/m) as a supplementary sulphide removal additive and also raised concerns regarding the lack of a testing procedure to monitor concentration. This issue was regarded as being very important on the grounds of the significant risk that existed in the absence of more accurate method of monitoring scavenger concentration other than just mass balance calculations. The lack of ability to measure scavenger concentration more precisely in the invert emulsion fluid returned to the liquid mud plant (LMP), led to increased cost for the operator to maintain a safe concentration. This paper discusses the design of a new method to be used in both OBM and WBM during field applications of the scavenger. The method is now used to monitor the excess scavenger in all the wells drilled in the Karachaganak field and to design subsequent treatments. The method has also contributed to improving the level of safety in the operation. The use of the proper scavenger concentration in combination with excess lime provides a primary and secondary barrier for protection against the influx of H2S
- Asia > Kazakhstan > West Kazakhstan Region (1.00)
- Asia > Kazakhstan > Atyrau Region > Caspian Sea (0.24)
- Asia > Kazakhstan > West Kazakhstan > Uralsk Region > Precaspian Basin > Karachaganak Field (0.99)
- Asia > Kazakhstan > Atyrau Oblast > Caspian Sea > Precaspian Basin > Kashagan Field (0.99)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Health, Safety, Environment & Sustainability > Health > Noise, chemicals, and other workplace hazards (1.00)
Summary A new scavenger has been developed that relies on the affinity between iron and sulfide. The active chemical is a form of ferrous iron complexed with a carbohydrate derivative. It is highly soluble in the brine phases of water-based mud (WBM) and will not precipitate at pH values greater than 12. When the iron is in solution, the reaction with sulfide is instantaneous and complete. This paper deals with the environmental implications of zinc vs. iron and the development of the new scavenger. It presents details of case histories concerning operations on a reservoir containing 25% hydrogen sulfide (H2S). Even in these demanding conditions, there was no H2S at surface. Introduction The presence of free H2S in subterranean deposits can represent a serious safety problem while drilling. The circulating drilling mud brings the toxic, flammable gas back to the surface, where it can be released and can create a severe hazard to rig personnel and others. Release of the gas can be controlled, to some extent, by keeping the pH value of the mud above 10 - this drives the H2S to the ionic-sulfide form and suppresses the concentration of the covalent H2S form. A low concentration of covalent H2S in the mud will be reflected in low vapor pressure of the gas, causing release to be less of a problem. However, elevating the pH value is not a permanent solution because the mud system will have a finite capacity, making it unable to hold an indefinite quantity of H2S or cope with an influx of the gas. Furthermore, increased lime concentration is not a satisfactory solution to the problem. Calcium hydroxide readily reacts with sulfide, but it is a long established fact that calcium sulfide readily dissociates 3 and allows release of H2S if the pH value should decrease (e.g., because of depletion or an influx of CO2 or H2S). Any preferred method of preventing release of H2S should ideally have the ability to remove the sulfide by converting it rapidly in a nonreversible way to a safe form. For many years, zinc compounds, which readily form zinc sulfide, have been used. This reaction immobilizes the sulfide very effectively unless the pH value of the system is allowed to fall below approximately 4, which is unlikely. Zinc compounds can be used in solution form (e.g., chelated zinc) or, more commonly, as insoluble solids, such as zinc oxide or basic zinc carbonate. Zinc chelate remains stable in solution in drilling mud at high pH values until in contact with the sulfide ion, where upon the chelate decomposes to precipitate zinc sulfide. This reaction is very rapid and efficient. In the case of solid zinc oxide or carbonate, the overall sulfide reaction is significantly slower. The reaction with the surface of the solid particles is rapid, but diffusion of the sulfide ions into the interior of the solid is required thereafter, thus slowing the subsequent reaction. In addition, at pH 11 or higher, solid-zinc scavengers can contribute to rheological or filtration properties because of the formation of zincates and the release of carbonate. Although zinc compounds provide an effective H2S treatment, the major disadvantage of using such scavengers is the potential environmental impact. Zinc is a conservative, heavy-metal pollutant that does not break down through time. The fate of the zinc - either as the sulfide or in its unreacted form - will be to remain with the drill cuttings that are septed by the solids control equipment or to remain in the residual liquid mud. Both of these waste streams may be destined for disposal in the sea or on land. In both cases, the presence of zinc represents a potential source of serious contamination. Zinc - Environmental Implications Zinc is present naturally in soils at concentrations from 10 to 300 mg/kg and in marine sediments at concentrations between 5 and 4000 mg/kg. Although the metal (in trace concentrations) is an essential plant element, it is toxic to plants at soil concentrations in excess of 600 mg/kg and toxic to marine animals at low concentrations (Table 1). In the case of oilfield mud-pit closure in the U.S., an allowable level of 500 mg/kg or less total zinc is sometimes suggested. However, for landscaped areas, this still may lead to some plant toxicity, and there also may be problems with leachate from soils carrying such a high load of metals, causing local impacts on ground and surface waters. The American Petroleum Inst. recommends maximum soil concentrations of 1400 mg/kg total zinc. European guidance triggers cleanup action when zinc exceeds 300 mg/kg for any area where plants may subsequently be grown. In situations where it is required to reuse nonsalt drill cuttings for fill-in on construction and landscaping projects, the presence of zinc is clearly unacceptable. Discharge of zinc is forbidden in many international waters because of its toxicity to aquatic organisms (Table 1). As a result of regulatory guidelines and risk of environmental contamination, it is advisable that zinc-containing drilling-fluid chemicals should not be used in drilling-fluid formulations where reuse of reclaimed cuttings material is required. Thus far, some of the most valuable treatments for controlling H2S contamination have used blends of zinc compounds (such as carbonates or oxides) to absorb the H2S and leave zinc sulfide, a less toxic residue. The Exploration and Production Forum 10 recommends product substitution as a source-reduction method of reducing waste-disposal problems and associated costs; therefore, a less-toxic alternative to zinc was pursued. Iron as a Sulfide Scavenger The need for a new approach to control H2S in drilling mud was highlighted by the requirements of a new development in the Caspian area. On the basis of the experience from adjacent fields in that part of Asia, it was highly likely that the reservoir would be very rich in H2S. On the other hand, there was also a requirement to develop the field in accordance with high environmental standards in which no potentially toxic materials would be acceptable in drilling mud or drill cuttings. It was clear at the outset: a scavenger treatment based on zinc would not be appropriate for this development.
- North America > United States (0.66)
- Europe > United Kingdom > England (0.28)
- Well Drilling > Drilling Fluids and Materials (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Health, Safety, Environment & Sustainability > Health > Noise, chemicals, and other workplace hazards (1.00)
Abstract Drilling into a hydrogen-sulphide (H2S) rich formation presents risks that the highly toxic gas might be carried to the surface and released, thus creating a serious hazard. To mitigate this risk, it is standard practice to run the drilling mud at high pH and to include a sulphide scavenger. Commonly, such scavengers are based on iron oxide or on zinc compounds. Iron oxide has the advantage of being environmentally friendly but, at high pH, has a slow reaction rate. In contrast, the zinc-based scavengers have a faster action. In particular, chelated zinc, which is water soluble, has a very fast reaction rate. The action of the zinc in any form is to precipitate the sulphide as a zinc salt. Precipitation prevents release of hydrogen sulphide gas, but it contaminates the mud and cuttings with zinc. In many parts of the world, disposal of material containing zinc is a problem because it is regarded as a toxic heavy metal. For example, discharge is forbidden in many international waters and cuttings for disposal on land may have to be treated as special waste. E&P Forum recommends product substitution as a source reduction method of reducing waste disposal problems and associated costs. Accordingly, a less toxic alternative was pursued. A new scavenger has been developed that relies on the affinity between iron and sulphide. The active chemical is a form of ferrous iron complexed with a carbohydrate derivative. It is highly soluble in the brine phases of water-based mud and will not precipitate at a pH over 12. Because the iron is in solution, the reaction with sulphide is instantaneous and complete. The paper deals with the environmental implications of zinc vs. iron and the development of the new scavenger. The paper will present details of case histories concerning operations on a reservoir containing 25% H2S. Even in these demanding conditions, no H2S was detected at the surface. Introduction It is well known that the presence of free H2S in subterranean deposits can represent a serious safety problem while drilling. The circulating drilling mud brings the toxic, flammable gas back to the surface where it can be released and create a severe hazard to rig personnel and others. Release of gas can be controlled to some extent by keeping the pH of the mud above 10; this helps ensure that most of the sulphide is held in the ionic sulphide form rather than as the covalent H2S form. The low concentration of covalent H2S in the mud will be reflected in low vapour pressure of the gas so release will be less of a problem. However, elevating pH is not a permanent solution because the mud system will have only a finite capacity and will not be able to hold an indefinite quantity of H2S or cope with an influx of the gas. Furthermore, increased lime is not a satisfactory solution to the problem. Calcium hydroxide readily reacts with sulphide but calcium sulphide readily dissociates and allows release of H2S if the pH decreases due to depletion or an influx of carbon dioxide or hydrogen sulphide. Ideally, any preferred method of preventing release of H2S should be capable of removing the sulphide by converting it rapidly in a nonreversible way to a safe, innocuous form. For many years, zinc compounds that readily form zinc sulphide have been used. This reaction immobilises the sulphide very effectively unless the pH of the system is allowed to fall below about 4, which is unlikely. Zinc compounds can be used in solution form, for example, chelated zinc or more commonly as insoluble solids such as zinc oxide or basic zinc carbonate. Zinc chelate remains stable in solution in drilling mud at high pH until it contacts the sulphide ion, whereupon the chelate decomposes to precipitate zinc sulphide. This reaction is very rapid and efficient. In the case of solid zinc oxide or carbonate, the overall sulphide reaction is significantly slower. The reaction with the surface of the solid particles is rapid but diffusion of the sulphide ions into the interior of the solids is required thereafter, thus slowing the subsequent reaction. In addition, at pH 11 or higher, solid zinc scavengers can contribute to rheological or filtration properties as a result of formation of zincates and release of carbonate.
- Europe (0.95)
- North America > United States > Texas (0.28)
- Well Drilling > Drilling Fluids and Materials (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Health, Safety, Environment & Sustainability > Health > Noise, chemicals, and other workplace hazards (1.00)
This paper was prepared for presentation at the 1999 SPE International Symposium on Oilfield Chemistry held in Houston, Texas, 16-19 February 1999.
- Asia > Middle East (1.00)
- North America > United States > Texas > Harris County > Houston (0.68)
- Production and Well Operations > Well Intervention (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Health, Safety, Environment & Sustainability (1.00)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (0.69)
This state-of-the-art paper discusses the reaction chemistry of commercial scavengers in water-base drilling fluids. Parameters that affect the reliability, of these materials for removing sulfides are emphasized. Practical problems of scavenger use, such as effects on mud performance, Practical problems of scavenger use, such as effects on mud performance, how to add the scavenger to mud, and rig-site monitoring methods, are considered. Introduction Excessive risks may be incurred from unquestioned reliance on sulfide scavengers during H2S drilling. Such risks can result from a lack of reliable information about how the scavenger should function and what factors (chemical and physical) control its behavior in a mud. A need for a summary about this often controversial subject prompted us to write this paper. We conclude that at prompted us to write this paper. We conclude that at present, no available commercial product approximates present, no available commercial product approximates die "ideal scavenger" defined here. Some products offer advantages, while some have major disadvantages because of characteristics of their chemical type and the mud's influential environment. Differences in chemical behavior in a mud are very important for safe H2S drilling, especially if a scavenger is being relied on greatly for H2S control and safety.We based the general scavenger chemistry presented here on the sulfide chemistry in the literature. Field experience with scavengers influenced aspects of this paper, but our specific laboratory studies and those of paper, but our specific laboratory studies and those of others are the major foundation for comments on factors influencing scavenger behavior in mud systems. Summary of Scavenger Application This summary of the practical aspects of using or not using a chemical as a sulfide scavenger in muds is based on discussions given later of background chemistry and test results. Only two types of scavengers are being marketed to the drilling industry currently:zinc-base chemicals and iron-oxide, Fe O. Copper compounds, although used in the past, are not considered satisfactory today because of drillpipe corrosion caused by reaction of copper ions with iron. No Scavenger A scavenger may not always be needed to control minor sulfides that result from drilling or similar small amounts of H2S entering a mud, although companies' policies may vary on this practice. A mud's natural scavenging capacity plus neutralization by mud alkalinity often are enough to control a minor amount of sulfides on a day-today basis. A change in operations, such as increasing mud weight, may reduce a small H2S influx to a negligible amount; then a scavenger is not needed. Where H2S influx could occur, it is important to measure the mud's soluble sulfide content frequently and quantitatively and to be prepared to add a scavenger if persistent filtrate sulfides appear. persistent filtrate sulfides appear. Zinc-Base Scavengers Two general types of zinc-base scavengers are now available;very slightly water-soluble inorganic compounds, the most common being basic zinc carbonate; and highly water-soluble organic zinc chelate compounds. For mud applications over a broad pH range, zinc-base additives provide effective scavenging by a rapid and irreversible reaction with sulfides to form solid ZnS. JPT P. 787
- Geology > Mineral > Oxide > Iron Oxide (0.50)
- Geology > Mineral > Sulfide > Iron Sulfide (0.49)
- Geology > Mineral > Native Element Mineral > Copper (0.47)
- Well Drilling > Drilling Fluids and Materials > Drilling fluid selection and formulation (chemistry, properties) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Health, Safety, Environment & Sustainability > Health > Noise, chemicals, and other workplace hazards (1.00)