CALCIUM HALIDE BRINES

Transcription

1 CALCIUM HALIDE BRINES halides are divalent salts that consist of one calcium ion associated with two halide ions. The halide ions that are commonly used in clear brine fluids include chlorides and bromides. halides are classified as ionic salts, which refers to its ability to disassociate completely into ions in water. halide is a manufactured product. bromide is produced by the reaction of hydrobromic acid or bromine gas and limestone or slaked lime. chloride is produced by the reaction of hydrochloric acid and limestone or as a by-product of the Solvay process. The chemical properties of both salts are listed in Table 1. chloride and bromide salts have an unusually high heat of solution. Dissolution of the dry salts should be done in a controlled manner due to the amount of heat generated as the salts dissolve. chloride and bromide are hygroscopic and deliquescent. The solid material, when exposed to the atmosphere, can absorb water until it forms a solution. chloride and bromide salts are used in the oilfield as a single salt brine or as a multiple salt blend brine. halide brines can be blended as a combination of calcium chloride and bromide, and in combination with zinc bromide salts. halide brines are used as completion and packer fluid and in formulation of PayZone fluids. fluids have the desirable properties to minimize formation damage cause by solid invasion, and shale dispersion. VISCOSITY Viscosity can be defined as the internal friction of a liquid. Viscosity is an important parameter for consideration in the oilfield due to its Apparent Viscosity, cp Table 1. Physical Properties of Halide Properties Chloride Bromide CHEMICAL FORMULA CaCl CaBr MOLECULAR WEIGHT CAS No EINECS No PHYSICAL APPEARANCE White granules/pellets White granules/crystals SOLID HYDRATES CaCl, CaCl H O, CaCl H O, CaCl 4H O, CaCl 6H O Temperature, deg. F Figure 1: Viscosity of calcium halide brines impact on hydraulics. The viscosity of a fluid is used in calculating fluid behavior under dynamic conditions such as fluid flow regime, frictional pressure, equivalent circulating density and pump pressure. halide brines are nearly Newtonian fluids. Newtonian fluids are defined as fluids that have a lin- ear shear stress to shear rate relationship. The viscosity of calcium halide brines as a function of temperature is given in Figure 1. The viscosity of mixed salt brines are sensitive to the composition of the salts. 9.5 ppg CaCl 11.6 ppg CaCl 1.8 ppg CaCl /CaBr 14 ppg CaCl /CaBr 14. ppg CaBr CaBr, CaBr 4H O, CaBr 6H O MELTING POINT 144 o F 1346 o F BULK DENSITY [anhydrous] lb/ft lb/ft 3 ph HEAT o F 0.6 cal./g/ o F [11.6 ppg CaCl ] 0.47 cal./g/ o F [14. ppg CaBr ] MAXIMUM BRINE 70 o F 11.8 ppg 15.1 ppg TETRA Technologies, Inc. Page 1

2 PH halide brines are nearly neutral in ph with values ranging from neutral to slightly alkaline. The alkalinity in calcium chloride and calcium bromide fluids is a by-product of its manufacturing process. The ph of calcium halide brines can be adjusted. The ph can be raised with lime [CaO] and slaked lime [Ca(OH) ]. Other highly soluble alkaline materials such as caustic soda [NaOH] should be used with caution to avoid precipitation of calcium hydroxide [Ca(OH) ] in the brine. The ph of calcium brines can be lowered with acids such as acetic acid [CH 3 COOH], hydrobromic acid [HBr] and hydrochloric acid [HCl]. The use of acids such as hydrofluoric [HF] and sulfuric [H SO 4 ] should be avoided to prevent undesirable precipitation. Extreme alteration of the brine ph may impact upon its corrosion rates, fluid and formation compatibility, and elastomer compatibility. CRYSTALLIZATION TEMPERATURE CRYSTALLIZATION TEMPERATURE, o F ppg CaCl ppg CaCl 1.8 ppg CaCl /CaBr 13.0 ppg CaCl /CaBr 13.0 ppg CaCl /CaBr PRESSURE, Psi Figure : Pressure crystallization temperature of calcium halide brines The general measurement of crystallization temperature used in the oilfield is the true crystallization temperature (TCT). The data on TCT values as a function of composition for calcium halide brines are given in Appendix A, Tables 7 to 9. The recommended TCT of a brine should be several degrees lower than the lowest temperature that the fluid will encounter. The minimum ambient temperature and seabed temperature should be taken into consideration in determining the TCT of a working brine. A recent discovered phenomenon is the impact of pressure on brine crystallization temperature. This phenomenon is referred to as pressure crystallization temperature (PCT). High pressure has been observed to increase the crystallization temperature of brines. In most cases, elevated temperatures are accompanied by high pressures, except in the case of deep-water exploration. In deepwater exploration, low seabed temperature coexist with high pressures from existing hydrostatic pressure or are artificially induced (i.e., during BOP testing). brines can experience significant PCT effect as illustrated in Figure. Wells that are prone to PCT effects should utilize a brine that is rated for the maximum encountered pressure experienced at the minimum temperature.. DENSITY The density of clear brine fluids is derived from dissolved salts. Brine densities are sensitive to changes in temperature (thermal expansion) and pressures (compressibility). The API standard for reporting brine density is referenced at 70 o F. The density of calcium halide brines measured at surface should be corrected using Equation 1. The correction factor used in equation 1 is given graphically in Figure 3 as derived from the polynomial equation referenced in API [Bulletin 13J, nd Edition, March 1995]. Brine crystallization temperature can be defined as the maximum temperature at which solids are formed. These solids can be salts and/or ice. All efforts should be made to avoid solids coming out of solution. The various problems that can arise from solids coming out of solution include loss in fluid density and solidifying of the entire fluid, causing plugging problems. Correction Factor Equation 1. D 70 = D m +(T m -70)xC f D 70 : corrected density at 70 o F, ppg D m : measured density at T m, ppg T m : temperature at which density was measured, deg. F Density, ppg Figure 3: Density correction factor Page TETRA Technologies, Inc.

3 In calculation of hydrostatic pressures or equivalent circulating density exerted by a brine in the wellbore, simultaneous application of the thermal expansion and compressibility factors must be applied. These calculations are easily done by TETRA s TP-Pro Program. CORROSION halide brines have relatively low to moderate corrosion when used at their natural neutral ph. Table presents corrosion rates of various densities of calcium brines. The common factors that have a tendency to accelerate corrosion of calcium halide brines include high temperatures, introduction of oxidizers, and contamination of acidic gases such as carbon dioxide and hydrogen sulfide. chloride brines should be carefully screened for applications in chrome alloys to avoid chloride stress cracking. Chloride stress cracking is a phenomenon induced by physical stress in the presence of chloride fluids that can result in catastrophic failures. The factors that influence chloride stress cracking include alloy type, alloy hardness, temperature, stress, chloride concentration, and contaminates. Single salt calcium bromide brines are sometimes utilized to avoid a chloride brine system and its associated problems with chloride stress cracking. Common additives used in corrosion treatment of calcium halide brines include oxygen scavengers, corrosion inhibitors, anti-scaling agents and biocides. Oxygen scavengers are reducing agents that chemically react with elemental oxygen. Oxygen is one of the parameters that promotes corrosion and it is essential to eliminate oxygen in wells utilizing chrome alloys. Oxygen scavengers are consumable additives and require continuous treatment in an open system. Table. Corrosion Rates of Halide Brines Fluid Temp. Test Period Corrosion inhibitors utilize a wide variety of chemistries to retard corrosion. Clear brine fluids are generally treated with a single application of corrosion inhibitors. Anti-scaling agents are utilized in environments that are prone to induce scales. Anti-scaling agents are designed to alter the properties of the solids that form such that the particle size are smaller, dispersible and nonscaling. Formation of scales can promote localized corrosion and formation damage. Biocides are used to kill bacteria that can produce corrosive by-products such as sulfides or slime formers which can promote localized corrosion. Biocides should be added to the brine early in order to give the biocide sufficient kill time. FLUID COMPATIBILITY halide brines have some compatibility issues. The calcium ion is generally the problematic ion. It can be the source of scaling problems such as calcium carbonate [CaCO 3 ] and calcium sulfate [CaSO 4 ]. The solubilities of some typically encountered calcium compounds are listed in Table 3. ions can also precipitate out polymers, surfactants and organics. Due Metal Coupon T Base Fluid to these considerations, fluid additives, formation water and other contacting fluids should be screened for compatibility with calcium halide brines prior to usage. The halide ion does not usually pose a significant Table 3. Solubilities Compound Acetate [Ca(C H 3 O ) ] Carbonate [CaCO 3 ] Fluoride [CaF ] Formate [Ca(COOH) ] Hydroxide [Ca(OH) ] Sulfate [CaSO 4 ] Sulfide [CaS] Inhibited Fluid 10.0 ppg CaCl 10 o F 30 days N mpy 0.6 mpy [TETRAhib ] 10.0 ppg CaCl 10 o F 30 days J-55.9 mpy 0.8 mpy 10.0 ppg CaCl 300 o F 30 days N mpy 1. mpy 10.4 ppg CaCl 40 o F 30 days N-80.9 mpy 1.4 mpy 10.4 ppg CaCl 40 o F 30 days 13 Cr 0.4 mpy 0.06 mpy 1.5 ppg CaCl /CaBr 40 o F 30 days N mpy 1.5 mpy 1.5 ppg CaCl /CaBr 40 o F 30 days 13 Cr 0.5 mpy 0.08 mpy 14.0 ppg CaCl /CaBr 00 o F 30 days S13 Cr 0. mpy 0.1 mpy [TETRAhib Plus] 14.0 ppg 350 o F 5 days N mpy 4.5 mpy CaCl /CaBr [TETRAhib Plus] Solubility in o F 1.0 wt.% 0.14 wt.% wt.% 13.9 wt.% 0.18 wt.% 0. wt.% 0.01 wt.% compatibility problem. It is highly soluble with most cations encountered in the oilfield. halide brines are generally compatible with most oilfield elastomers. A general recommended guideline for compatibility of calcium brines with elastomers is given in Table 4. Elastomer formulations are subjected to changes and vary with manufacturers. Therefore the TETRA Technologies, Inc. Page 3

4 Table 4. Guidelines for Elastomer Compatibility Material Temp. Rating AFlas <450 o F Satisfactory Chemraz <400 o F Satisfactory Fluorel, filled <350 o F Satisfactory Kalrez <550 o F Satisfactory Neoprene <50 o F Swells Nitrile <300 o F Satisfactory Teflon <35 o F Satisfactory Viton <450 o F Satisfactory brines is listed in Table 6. The equipment for each category in Table 6 is listed in the order of increasing risk of exposure. Repeated or prolonged skin contact with calcium brine should be avoided. Due to the high salt concentration of brines, use of any leather material is not recommended. The minimum recommended safety equipment available on well sites utilizing brines should include an eyewash facility and a safety shower. elastomer manufacturer and/or tool vendor should always be consulted prior to application. The compatibility of a brine to an elastomer may be altered by introduction of additives such as corrosion inhibitors and extreme fluid ph adjustment. SAFETY & ENVIRONMENTAL halide brines are hygroscopic fluids that can be a severe irritant when it is ingested, inhaled or comes in contact with eyes and skin. Consult the material safety data sheet for compete information. The hazard ratings and transportation classification for both salts are given in Table 5. Neither calcium salts are regulated as a hazardous material for transportation. NFPA Rating Hazard Symbol Risk Phrases Transport Information Table 5. Safety Chloride Health 1 Fire 0 Reactivity 0 XI [irritating substance] R 36 [irritating to eyes] Not Regulated Bromide Health 1 Fire 0 Reactivity 0 None Listed None Listed Not Regulated Table 6. Personal Protective Equipment Eyes Skin Clothing Respirators Safety glasses Chemical Safety goggles Face shield & goggles Water impervious gloves Slicker suit or Water impervious gloves Follow respirator standards 1) OSHA, 9 CFR ) European Standard EN 149 chloride and calcium bromide brines are environmentally acceptable completion fluids. completion fluids can be used in the United States and in the North Sea without restriction. chloride and calcium bromide are listed in OSPAR Commission s PLONOR list. The OSPAR Commission represents a convention of European countries for the protection of the marine environment in the North-East Atlantic. The PLONOR list is a compilation of chemicals used and discharged offshore which are deemed to be pose little or no risk to the environment. The recommended personal protective equipment for calcium halide Page 4 TETRA Technologies, Inc.

5 Brine o F [lb/gal] Pressure Gradient [psi/ft] APPENDIX A Table 7. Composition of Chloride Brines Water [bbl] CaCl wt.% CaCl [wt.%] Chloride Crystallization Temperature [TCT, o F] ,500 57, ,500 64, ,500 73, ,00 81, ,600 89, ,900 97, ,00 104, , , , , ,00 18, , , ,500 14, , , ,00 157, ,00 164, , , , , , , , , ,00 196, ,800 03, ,800 10, ,400 16, ,000 3, ,600 9, ,00 35, ,900 4, TETRA Technologies, Inc. Page 5

6 Brine o F [lb/gal] Pressure Gradient [psi/ft] APPENDIX A Table 8. Composition of Bromide Brines Water [bbl] CaBr CaBr [wt.%] Bromide Crystallization Temperature [TCT, o F] , , ,400 31, , , ,400 34, , , , , , , , , , , , , , , ,00 371, , , , , , , , , , , , , , , , , , , ,300 43, ,700 49, , , , , , , , ,500 45, , , ,900 46, , , , , , , , , , , Page 6 TETRA Technologies, Inc.

7 Brine o F [lb/gal] APPENDIX A Table 9. Composition of Chloride/ Bromide Brines Pressure Gradient [psi/ft] Water [bbl] CaCl CaBr Chloride Bromide Crystallization Temperature [TCT, o F] ,800 50,000 13, ,100 44,700 7, ,500 39,400 41, ,800 34,100 53, ,00 9,100 66, ,500 4,100 79, ,800 19,000 91, ,100 14,00 103, ,400 09, , ,700 04,600 17, ,000 00, , ,00 195, , , ,900 16, , , , ,100 18, , , , , , ,600 05, , ,400 16, ,00 165,300 6, , ,00 36, , ,00 46, , ,300 56, ,00 149,400 66, , ,600 75, , ,900 85, , ,100 94, ,00 134, , , ,800 31, ,600 17,300 31, ,900 13, , ,000 10,00 339, , , , , , , , , , , ,900 37,900 TETRA Technologies, Inc. 505 Interstate-45 North The Woodlands, TX Focused on Energy. Dedicated to Service. Page Copyright 00 TETRA Technologies, Inc. All rights reserved. TETRA, TETRAhib, TP Pro and the TETRA logo are trademarks of and PayZone is a registered trademark of TETRA Technologies, Inc. Rev 1/0