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IESTPORTTECbullILIH CUITEI IHEHITIDUL
Gas Hydrates Technology
DT-97-174 December 1997
Novel Hydrate Prediction Methods for Drilling Fluids - Phase 2
Final Report
By
M Tumey J Trenery M Yousif
Westport Technology Center International 6700 Portwest Drive
Houston Texas 77024 (281) 560middot4666
(713) 864middot9357 (Fax) wwwwestport1com
Prepared for JIP WO H09526H200
Westport Technology Center International makes no representations or warranties either express or implied and specifically provides the results of this report as is based on the information provided by client
WESTPORT TECHNOLOGY CENTER INTERNATIONAL
Novel Hydrate Prediction Methods for Drilling Fluids- Phase 2
Prepared by Monica Tumey and Majeed Yousif
Work Done by Monica Tumey John Trenery Majeed Yousif
FINAL REPORT December 1997
-
Westport Technology Center International 6700 Portwest Drive
Houston Texas 77024 281-560-4666
Fax 713-864-9357 wwwwestport1com
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- Table of Contents
1 Executive Summary
2 Project Deliverables
3 The Experimental work and results
4 Features of the hydrate prediction model WHyP
41 WHyP input and output
42 Prediction of the Hydrate Phase Line - identifying the gas kick fluid 421 Statistical thermodynamic method 422 Gas specific gravity method
43 Prediction of the Hydrate Temperature Suppression aT - identifying the drilling fluid
431 Mud Activity Method 432 Drilling Fluid Composition Method 433 Resistivity and Density Method
5 Results - the model calculations compared to experimental data
51 Prediction of the hydrate phase line of a gas mixture with no inhibitor in the drilling fluid
52 Prediction of the hydrate temperature suppression aT using the measured water activity
53 Prediction of the hydrate temperature suppression aT using the inhibitor concentration ( wt)
54 Prediction of the hydrate temperature suppression aT using the measured mud filtrate resistivity and density
6 References
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1 Executive Summary
The main objective for this two-phase Joint Industry Project (JIP) was to develop methods and computer software (model) to predict the hydrate equilibrium conditions of drilling fluids
In phase 1 of this project which was completed in June 1996 we developed a novel method to predict the hydrate temperature suppression using the resistivity and density of the drilling fluid filtrate The method has the following features (1) useful tool for rapid on-site determination of gas hydrate temperature suppression in drilling muds (2) input parameters can be easily measured on site (filtrate resistivity and density at ambient pressure and temperature) (3) valid for drilling fluids inhibited by salts andor mixtures of salts and glycols (4) valid for temperature suppression of up to 55degF (5) except for the type of glycol no information is needed about the mud composition (6) valid for glycols and chloride salts concentrations of (0-30 wt) and (5-30 wt) respectively
In phase 2 of this JIP we developed a new hydrate prediction model that is specifically tailored for use by drilling personnel The model is named WHyP for Westport Hydrate Prediction Program for Drilling Fluids WHyP is based on the statistical thermodynamic theory of van der Waals and Platteeuw and incorporates the hydrate temperature suppression methods developed in Phase 1 as well as other available methods WHyP
is Windows 95reg compatible and is linked to an Excel interface for user friendly data inpuVoutput The model is designed to be simple and easy to run while at the same time maintaining high flexibility to accept a wide range of input data
WHyP can be run in a prediction mode or a design mode The design mode is a unique feature added to allow an interactive execution of the program With the design mode the user can determine the appropriate amount of a selected inhibitor to suppress hydrate formation at a given mudline pressure and temperature conditions
A trial version of the software was mailed to the sponsors in July 1997 for testing Since then this version was revised based on the comments received from Patrick Shuler (Chevron) and Richard Chambers (BPX) as well as our in-house testing A final version of the software is attached to this report Ultimately since no software product can be considered complete Wesport Technology will continue to maintain the software with upgrades distributed to the sponsors annually
To assess the accuracy of the model predictions we compared the predictions of the model to measured gas hydrate temperature suppression of 101 solutions of mixed salts and glycols The measured hydrate temperature suppression LiT was in the range of 0 to 47degF The accuracy of the model in predicting the hydrate equilibrium temperature is within 175degF when using the drilling fluid composition 334degF when using the mud filtrate resistivity and density and within 846degF when using the measured activity
This report also provides the background for the model development and the experimental measurements obtained as part of phase 1 and 2 of this JIP
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2 Project Deliverables
bull All data generated under phase 1 of the project
bull A user-friendly IBM-PC Windows 95reg based menu-driven hydrate prediction model specifically tailored for drilling and completion fluids The model will accept either of the following parameters
bull For drilling fluids of known composition input weight fraction of each inhibitor bull For drilling fluids of unknown composition input the following measured
filtrate properties Resistivity density temperature glycol density and glycol molecular weight
bull Measurements of solution activity and hydrate equilibrium for bull Na-Formate (10 20 40 wt) bull K-Formate (15 30 50 wt) bull ZnBr2 (10 20 30 wt) bull CaBr2 (10 20 30 wt)
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3 The experimental work and results
Table 1 contains selected properties of 101 different solutions inhibited for hydrate temperature suppression All these data have been measured at Westport Some of the hydrate temperature suppression data were obtained previous to this project In chapter 5 the (composition activity or densityresistivity data are used in the WHyP model to calculate temperature suppression and the results are compared to the measured temperature suppression
Table 2 contains the gas hydrate equilibrium data of the 12 solutions measured in this project These data are used to determine hydrate temperature suppression
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Table 1 Measured Temperature Suppression Water Activity Density And Resistivity
0 ft t d I es e aqueous so ut1ons No Solution molarity
1 5 wt NaCl + 5 wt MeOH 088160 2 10 wt NaCl+ 10 wt MeOH 180329 3 28 wt KCI + 294 wt MeOH 036889 4 5 wt NaCl + 5 wto Ethylene Glvcol 089084 4 5 wt NaCl + 5 wt Ethylene Glycol 5 10 wt NaCl + 10 wtlo Ethvlene Glvcol 186175 6 20 wt NaCl + 1 O wt Ethylene Glycol na 7 10 wt NaCl+ 184141
10 wto Pronvlene Glycoi11
8 5 wt NaCl + 5 wt Glvcerol 089057 9 10 wt NaCl + 1 O wt Glycerol 187119 10 10 wto NaCl + 20 wt Glvcerol 1921243 11 10 wt NaCl + 30 wt Glycerol 1971374 12 20 wto NaCl + 10 wtlo Glvcerol 401127 13 20 wt NaCl + 20 wt Glvcerol 413262 14 20 wt NaCl + 20 wt Glycerol na 15 234 wt NaCl + 10 wt Glvcerol 485132 16 221 wto NaCl + 15 wt Glycerol 460198 17 208 wt NaCl + 20 wto Glycerol na 18 3 wt NaCl + 5 wt KCI + 055072058
5 wt Glvcerol 19 5 wt NaCl + 5 wt KCI + 095074183
15 wt Glvcerol 20 10 wt NaCl+ 10 wt KCI + 1991561126
1 O wt Glycerol 21 5 wt KCI + 5 wt Glvcerol 070057 22 5 wt KCI + 10 wt Glycerol 071114 23 1 O wt KCI + 1 O wt Glycerol 146118 24 5 wt CaCI + 5 wt Glvcerol 047057 25 5 wt CaCl2 + 20 wt Glycerol 049235 26 10 wt CaCI + 10 wt Glvcerol 100120 27 20 wt NaCl+ 20 wt GEO MEG na 28 53 wt NaCl + 128 wt AauaCol-S 096023 29 20 wt NaCl + 1 O wt AauaCol-S 397019 30 10 wto KCL + 10 wt AauaCol-S 146018 31 10 wt NaCl +10 wt KCI + 198156019
1 O wt AauaCol-S 32 20 wt Na-Formate + 335019
10 wt AauaCol-S 33 20 wt NaCl + 10 wt HF1 OON na 34 15 wt KCI + 30wt HF1 OON na 35 30 wt CaCI + 70 SvnTec na 36 5 wt NaCl 088 36 5 wt NaCl 37 10 wt NaCl 183 37 10 wtdego NaCP 1
38 125 wt NaCl 233 39 20wt NaCl 393 39 20wt NaCl 40 2044 wt NaCl 402 41 26wt NaCl 532 42 10 wt NaCl+ 10 wt KCI 195153
Water Density Activity at60degF
[ppg]
0957 8563 0897 8786 0947 8088 0902 8698
0929 9052 0796
8983
8702 9138 9355 9592
0802 9774 0796 10072
0632 10112 0680 10144
0947 8901
0921 9251
0744 9708
0967 8721 8795
0958 9095 0976 8787
9035 0962 9243 0813 10264
8805 0777 9680 0883 9096 0814 9680
0803 9513
0789 9847 0827 9931 0800 0915 8617
0899 8918
0886 9105 0820 9584
0833 9585 0728 9983 0834 9513
Temp Resistivity LlT Ref (oF) [ohm-m] [OF]
729 01459 860 a 718 00777 2100 a 721 04148 3500 696 01218 660 a 720 01301 660 a 729 01049 1680 a 716 00447 3970 d 770 01005 1804 b
770 01390 512 b 727 01131 1268 b 730 01259 1950 b 770 01559 2661 b 721 00642 3570 a 723 00614 4210 a 716 00802 4691 a 730 00683 4030 a 729 00602 4350 a
4590 a 720 01189 760 a
738 0 1195 1590 a
720 00466 2320 a
698 01057 335 a 770 01505 566 b 729 01066 910 a 721 01388 400 a 770 02151 823 b 730 01204 1010 a
3650 d 770 01932 740 b 714 00785 3660 d 720 00730 1160 d 723 00492 3050 d
720 00929 3020 d
3640 d 2990 d nh d
741 01325 375 b 739 01321 375 b 739 00594 842 b 734 00753 842 b 745 00635 1050 a 734 00516 2823 a 745 00414 2823 a 718 00446 2700 a
3520 a 718 00217 2090 d
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- Table 1 (continued)
-
No Solution molarity Water Density Temp Resistivity AT Ref Activity at 60F
[ppg) [F] [ohm-m] [F]
43 5wtKCI 069 8588 770 01316 162 b 44 10wtKCI 142 8862 770 00672 692 b
d 45 20wt KCI 306 0835 9513 721 00259 1700 46 5 wt CaCl2 047 8680 716 01259 234 b 47 5wt CaCl2 770 01449 234 b
a 48 1442 wt CaCI na 0989 1400 49 15 wt CaCl2 153 0921 9452 741 00649 1520 a 50 1922 wt CaCl2 na 0908 721 00489 2190 a 51 21 wt CaCI na 2300 52 26 wt CaCI na 716 00492 3900 53 1Owt Na-Formate 157 0846 8903 727 01140 617 c 54 15 wt Na-Formate 241 0962 9130 725 00993 55 10 ooa (176 wtl Na-formate 313 0740 10068 56 11 nnn (194 wt) Na-formate 374 0676 10944 57 20 wt Na-Formate 331 0811 9395 725 00829 1493 c 58 30 wt Na-Formate 53 0775 10021 734 00752 2993 c 59 40 wt Na-Formate 759 0757 10765 718 00981 3920 d 59 40 wt Na-Formate 762 0938 10806 3920 d 60 5 wt K-Formate 061 0986 8581 732 02602 61 10 wt K-Formate 125 0970 8806 734 01781 62 15 wt K-Formate 194 0860 9089 873 d 63 12 nnn (171 wt K-formate 293 0584 12033 64 131nnn1187 wt K-formate 347 0562 13052 65 20 wt K-Formate 264 0957 9255 727 00759 66 30 wt K-Formate 423 0784 9901 736 00341 2395 c 67 40 wt K-Formate 595 0733 10444 734 00380 68 50 wt K-Formate 794 0670 11149 nh 69 21 wt Ca-Nitrate 283 0869 9430 721 00848 740 d 70 15 wt NaBr 152 0944 8689 700 00807 71 20 wt NaBr 229 0888 9830 718 00556 1672 a 72 30 wt NaBr 375 0783 10743 698 00401 2980 a 73 5 wt CaBr2 026 0991 8674 720 02144 74 10 wt Ca Br2 054 0892 9063 148 c 75 15 wt Ca Br2 085 0976 9452 698 00792 76 20 wt Ca Br2 113 0844 9452 998 c 77 30 wt Ca Br2 179 0805 9932 729 00492 2324 c 78 5 wt Zn Br2 036 0854 8704 720 02738 79 10 wt Zn Br2 075 0919 9063 736 01356 084 c 80 15 wt Zn Br2 118 0830 12084 723 01148 81 20 wtZn Br2 164 0875 9452 736 00905 700 c 82 30 wt Zn Br2 271 0844 9932 732 00866 1420 c 83 5wtMe0H 154 0917 8251 84 10wt MeOH 305 0896 8146 85 15 wt MeOH 454 0887 8094 86 40wt MeOH 1168 0833 7808 3700 87 50wtMeOH 1453 0827 7768 88 5 wt Ethylene Glycol 081 0904 8388 89 10 wt Ethvlene Glvcol 163 0877 8444 90 15 wt Ethylene Glycol 246 0853 8500 91 20 wt Ethvlene Glvcol 33 0844 8556 92 30 wt Ethylene Glycol 501 0833 8651 93 5 wt Glycerol na 0962 94 10 wt Glvcerol 111 8543 700 a
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Table 1 (continued)
No Solution molarity Water Density Temp Resistivity tT Ref Activity at 60degF [OF] [ohm-m] [OF]
[ppg]
95 125 wt Glvcerol na 550 a 96 20 wt Glvcerol 226 8697 1100 a 96 20 wt Glvcerol 226 950 a 97 30 wt Glvcerol 35 0942 8959 1672 a 97 30 wt Glycerol 35 0942 8959 1480 a 98 40 wt Glvcerol na 0826 99 5 wt AauaCol-S 0084 0920 8397 100 1 o wt AauaCol-S 017 0938 8512 210 d 100 1 0 wt AauaCol-S 0169 0917 8453 210 d 101 15 wt AauaCol-S 026 0872 8527 0density at 77 F measured m JIP phase 1 molarity= mo I liter solution nh =No hydrate formation in test na = Not available
The sources of the measured temperature suppressions (ref Table 1 column 9) are bull a Yousif amp Young 19874
bull b Phase 1 (this project) 1
bull c Phase 2 (this project) bull d Ebeltoft Yousif and Soergaard 199714
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Table 2 Measured Gas Hvdrate Eauilibrium Temperature and Pressure
Solution Run ID Temperature fdegF]
Pressure losial
10 wtoo Calcium Bromide CBRR1P5500 8150 5600 CBRR2P4000 7850 3800 CBRR3P3000 7500 2800 CBRR4P1500 6900 1330
20 wt Calcium Bromide CABR1P5500 7300 5080 CABR2P4000 7050 3820 CABR3P3000 6750 2840 CABR4P1500 6220 1363
30 wt Calcium Bromide CARR1P5500 5800 4850 CARR2P4000 5620 3785 CARR3P3000 5310 2855 CARR4P1500 4970 1525
1 O wt Sodium Formate NAFR1P5500 7560 5130 NAFR2P4000 7300 3680 NAFR3P3000 7100 2800 NAFR4P1500 6600 1280
20 wt Sodium Formate NFAR1P5500 6580 5000 NFAR2P4000 6450 3825 NFAR3P3000 6220 2980 NFAR4P1500 5720 1480
30 Sodium Formate NFMR1P5500 5000 4545 NFMR2P4000 4740 3595 NFMR3P3000 4480 2660 NFMR4P1500 4095 1264
1 0 wt Zinc Bromide ZBRR1P5500 8195 5230 ZBRR2P4000 7920 3972 ZBRR3P3000 7640 3010 ZBRR4P1500 7130 1503
20 wt0o Zinc Bromide ZNBR1P5500 7585 5085 ZNBR2P4000 7340 3955 ZNBR3P3000 7060 2985 ZNBR4P1500 6530 1430
30 wt Zinc Bromide ZNRR1P5500 6745 4820 ZNRR2P4000 6600 3817 ZNRR3P3000 6310 2825 ZNRR4P1500 5910 1465
15 wt Potasium Formate KFMR1P5500 7400 5065 KFMR2P4000 7150 3890 KFMR3P3000 6850 2980 KFMR4P1500 6430 1480
30 wt Potasium Formate KFAR1P5500 5710 4596 KFAR2P4000 5580 3870 KFAR3P3000 5310 2812 KFAR4P1500 4890 1532
50 wtoo Potasium Formate KFAR1P5500 No Hydrate Formation
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4 Features of the hydrate prediction model WHyP
WHyP is the state-of-the-art hydrate prediction model specifically tailored for use by drilling personnel To use the model only minimal prior knowledge of the phase
behavior of natural gas hydrates is required WHyP is Windows 95reg compatible and is linked to an Excel interface for user friendly data inputoutput The model is designed to be simple and easy to run while at the same time maintaining high flexibility to accept a wide range of input data The model can be run in a prediction mode or a design mode
The design mode is a unique feature added to allow an interactive execution of the program The design mode helps the user to interactively vary the amount and type of inhibitor to keep the mud system outside the hydrate region for a given BOP pressure and temperature The user must select one inhibitor and input the temperature and pressure conditions If the selected inhibitor is not adequate to inhibit hydrates at the specified mudline pressure and temperature the program will request that you abort
The following section describes the models used in WHyP For a closer study of these the references at the end of this report should be helpful Figure 1 shows the models used by WHyP The methods to determine the pure water line (line 1) are described in section 42 and section 43 treats the models for determining the temperature suppression tT
Figure 1 The Model Com onents -
-
By determining the phase line 1 and the tT phase line 2 which represents the hydrate equilibrium conditions of an inhibited mud can be determined as illustrated in Figure 1
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41 WHyP input and output
The computer program requires the characterization of both the hydrocarbon phase (the gas kick fluid) and the aqueous phase (drilling fluid) WHyP can be used for prediction of hydrate equilibrium at pressures ug to 10000 psi (700 MPa) It allows for a maximum temperature suppression of 558 F (310 degK) These limitations were set by the experimental data available during development of the model Anytime the concentration of the selected inhibitor(s) exceeds the saturation limit or the model accuracy in predicting the hydrate temperature suppression tT the program will abort
The WHyP program allows for input data in either SI or field units The output will be in the chosen unit system The user interface is built up through a series of screens starting by identifying the hydrate forming natural gas (section 42) Next the user identifies the drilling fluid in use (section 43) or asks the program to design a sufficiently inhibited mud (in the design mode) Finally the thermal conditions are specified WHyP will let you calculate either hydrate temperature at set pressure or hydrate pressure at set temperature The program can also calculate the entire hydrate equilibrium line (up to 10000 psi (700 MPa)) and plots up to 5 hydrate lines on the output sheet for visual comparison
42 Prediction of the Hydrate Phase Line - identifying the gas kick fluid
The program accepts both the composition of the fluid or its specific gravity
421 Statistical thermodynamic method
The statistical thermodynamic theory of van der Waals and Platteeuw2 represents the backbone for the WHyP model This part of the model provides the main predictive tool for the hydrate phase equilibrium of pure waternatural gas systems (shown as line 1 in Figure 1)
WHyP accepts the following species in the gas kick fluid
Table 3 Acceoted Gas Comoonents
Methane C1 Heotane n-C7 Hexadecane n-C16 Ethane C2 Octane n-C8 Heotadecane n-C17 Pronane C3 Nonane n-C9 Octadecane n-C18 lsobutane i-C4 Decane n-C10 Nonadecane n-C19 Normal Butane n-C4 Undecane n-C11 Eicosane n-C20 lsonentane i-C5 Dodecane n-C12 Carbon dioxide C02 Normal nentane n-C5 Tridecane n-C13 Nitroaen N2 Cvclonentane c-C5 Tetradecane n-C14 Hvdroaen sulfide H2S Hexane n-C6 Pentadecane n-C15
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WHyP assumes that there is sufficient water present to form hydrates The solubility of hydrocarbons in water is negligible It calculates equilibrium of structure I and II hydrates and allows for a 2 phase flash to account for gas and condensate
In the following is a brief introduction to the statistical thermodynamic approach to hydrate equilibrium calculations A more detailed description can be found in the literature2
bull Classical thermodynamics require energy (fugacity) balance at equilibrium of all components in the present phases This is used to calculate the gas hydrate equilibrium temperature or pressure using the composition of the kick fluid
A multiple component and multiple phase system is at thermodynamic equilibrium when the chemical potential micro of each component is the same in all phases
Van der Waals and Platteeuw calculated the chemical potential of water in the hydrate state from a fictitious state of empty lattice (MT) added the effect of the guest molecules (K) stabilizing the cavities (i)
Langmuir adsorption theory gives the probability (YK) of a cavity (i) being occupied by a hydrate forming molecule (K) CKi is the Langmuir adsorption constant at the specified temperature
A general expression for the chemical potential of water in the co-existing phase is made by relating it to some reference state (0)
Combined to the final equation of energy equilibrium of water in existing phases Li represents the difference between the fictitious empty lattice condition and the coshyexisting water phase (liquid or ice) at reference condition
Llmicroo -JT (Mio+ fgtC(T- To)) T+ s Ll~dP = ln(a )- v In(- middot)RT RT2 RT w L L YKo
0 ~ 0 I K
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-middot The water activity is the term in the energy balance that reflects the effect of hydrate
inhibitors
ln(fw)=lna~ w
WHyP uses the Suave-Redlich-Kwong equation of state to calculate the fluid phase fugacities of all components in all phases present
422 Gas specific gravity method
In the absence of a reliable composition of the gas kick fluid the statistical model of van 2
der Waals and Platteeuw cannot be used To overcome this difficulty (unknown gas composition) a specific gravity correlation3 is included in the program to determine the pure water line (line 1 in Figure 1 )
This empirical correlation uses only the specific gravity y of the kick fluid to predict the hydrate equilibrium temperature at a given pressure The method is less accurate than the thermodynamic approach of van der Waals and Platteeuw It is only to be used as a first estimate of the hydrate equilibrium temperature when gas composition data are not available The specific gravity correlation introduced in WHyP is an improvement over the previous method3
Included in the new specific gravity correlation are the hydrate equilibrium data measured since the publication of the original method in 1944 The equation developed and included in this computer code is
Tdeg F = -15428+ 24422ln(r)+ 12604In(Ppsia)
43 Prediction of the Hydrate Temperature Suppression ~T - identifying the drilling fluid
When the drilling fluid contains hydrate inhibitors such as salts and glycols other tools are required to determine the suppressing effect or~T of these inhibitors
With WHyP the user can chose to input the weight fraction of each inhibitor present in the drilling fluid or the mud filtrate resistivity and density A direct input of the measured or calculated solution activity can also be selected by the user
The advantage of the activity and the resistivity methods is that the hydrate temperature suppression jT can be determined for a drilling fluid of unknown composition
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431 Mud Activity Method
This method uses measured activity of the drilling fluid to predict the hydrate temperature suppression AT This is the most accurate of the methods provided that the activity measurements are good The water activity is a direct measure for inhibitor concentration according to classical thermodynamics
For the gas hydrate base line (line 1 in figure 1 ) the water activity is very close to unity This changes as impurities enter the water rich phase and in an inhibited system the term mostly effected by the impurities is the water activity The classical approach to determining gas hydrate equilibrium is by assuming that the water activity is the only parameter (in the energy balance) that effects the equilibrium temperature (or pressure) through the inhibition
432 Drilling Fluid Composition Method
This method determines the hydrate temperature suppression AT from the weight percentage of each inhibitor in the solid free mud formulation4
bull The method can be used for mixed inhibitors when the composition of the drilling fluid is known The WHyP model allows for use of the following inhibitors
Table 4 Accepted I nh1b1tor Components
Inhibitor Concentration limit (wt)
Inhibitor Concentration limit (wt)
NaCl 264 Methanol 400 KCI 255 Ethylene Glycol 400 CaCl2 300 Proovlene Glycol 400 NaBr 475 Glycerol 400 CaBr2 320 Polval1ltylene Glycol 400 ZnBr 320 NaCOOH 420
KCOOH 500
A correlation for mixed inhibitors was developed by Yousif and Young4 and further
improved in phase 1 of this project This model uses the assumption that inhibitors will shift the hydrate equilibrium temperature regardless of the pressure An empirical expression was developed giving the hydrate temperature suppression AT as a polynomial of the inhibitor concentration x
AT= 84998x + 1821x~ -3522~
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The inhibitor mole fraction Xn is calculated by Hammerschmidts equation for inhibitor concentration modified for mixed solutions
((( ) ) wtmiddot) wtL n-1 a+I -- +-shy- Mws Mwg
X - (wt)+ wt+ wtw L M M M f3mx
Ws Wg WW
where a is the mixtures degree of ionization and ~ is a correction factor accounting for the synergetic effects between salt and glycol in mixed inhibitors This factor was fitted to experimental data from a range of mixed solutions When the mud consists of either salts or glycol (not mixed) this factor equals zero and the inhibitor fraction converges to Hammerschmidts original equation A closer description of this expression is given in appendix A
433 Resistivity and Density Method
This method which was developed as part of phase 1 of the Novel Hydrate Prediction Methods Joint Industry Project determines the hydrate temperature suppression tT using the resistivity and density of the mud filtrate The resistivity and density used as input for this method must be measured at the same temperature This method is not valid for use when bromide or formate salts are present
The composition of mixed solutions of chloride salts (NaCl KCI CaCl2) and glycol can be calculated as functions of the resistivity and density
RmixPmix H wswg
After calculating the inhibitor fraction of the mixed solution the model proceeds with the method in section 432
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80
- Calculated bull60 bull Experimentala bull r bull l 40 UJ
a UJ
bullbull 20 bull
bull o==-+--~~--+~~~ 280 290 300 310
Temperature K
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5 Results - the model calculations compared to experimental data
51 Prediction of the hydrate phase line of a gas mixture with no inhibitor in the drilling fluid
In the following section measured gas hydrate equilibrium of selected gas mixtures from published literature are plotted with the equilibrium calculated using WHyP
511 Gas composition 906 wt C1 66 wt C2 18 wt C3 05 wt iC4 05 wt nC4 no inhibitor in the drilling fluid (Mcleod HO Campbell JM (1961 )5)
Figure 2 Hydrate Phase Equilibrium
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so~~~~~~~~~~~~~~~~~--__
--Methane70 --Propane -965degoC135ooC3
bull Methane ~ 60
50 bull Propanee 4o + 965ooC135ooC3
~ 30 0
20
10
0 f-==11shy260 270 280 290 300 310
Temperature [K]
80 --Methane70 --EthaneCi 60
0 -946ooC154C2~ 50
bull Methanef 40 Ethane 30 bull 946degoC154C20 20
10
0 i----dtlll 260 270 280 290
Temperature [K]
300 310
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512 8 9 10Gas composition 965 wt C1 35 wt C3 Shown with 100 wt C1 7 middot bull and 100
wt C39
1
no inhibitor in the drilling fluid (Mcleod HO Campbell JM (1961) 5)
Figure 3 H drate Phase E uilibrium
513 0 9 - Gas composition 946 wt C1 54 wt C2 Shown with 100 wt c1 1 middot bull bull
10 and 100 wt c 212131bull
no inhibitor in the drilling fluid (Mcleod HO Campbell JM (1961) 5)
Figure 4 H drate Phase E uilibrium
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10000
~
Ui ai ~
I en en Clgt ~
a
1000
--shy
1----middot---middot --- shy - shy- shy -shy - shy --middot-middot shy - shy
j --~--middot --middot bull
7 7- I
t---~-~
I shy 1bull + 10 wt CaBr2 --shy
I 1 20 wt CaBr2 ) I bull 30 wt Ca8r2
I I
40 50 60 70 80 90 100 110 Temperature [degF]
bull 10 wt ZnBr2
1 20 wt ZnBr2
bull 30 wt Zn8r2 1000-~-~--~-~--~-~--~~~
100 11040 50 60 70 80 90 Temperature [degF]
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52 Prediction of the hydrate phase line of a gas mixture with bromides and formates in the drilling fluid
In this section the experimental data in table 2 are compared to the model predictions
521 Gas composition Green Canyon Drilling fluid containing 10 20 and 30 weight CaBr2
Figure 5 Hydrate Phase Equilibrium
522 Gas composition Green Canyon Drilling fluid containing 10 20 and 30 weight ZnBr2
Figure 6 Hydrate Phase Equilibrium
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+ 1 O wt Na-Formate a 20 wt Na-Formate
bull 30 wt Na-Formate
30 40 50 60 70 80 90 100 110 Temperature [degF]
523
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Gas composition Green Canyon Drilling fluid containing 10 20 and 30 weight Sodium formate
Figure 7 Hydrate Phase Equilibrium
524 Gas composition Green Canyon Drilling fluid containing 15 and 30 weight Potassium formate
Figure 8 Hydrate Phase Equilibrium
~--I
30 40 50 60 70 80 90 100 Temperature [degF]
L___________ -------~
1
+ 15 wt K-Formatebull a 30 wt K-Formate
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53 Prediction of the hydrate temperature suppression tT using the measured water activity
When measured activity is used to identify the drilling fluid the deviations between measured and calculated temperature suppression tT is mainly due to measurement error The method is consistent with classical thermodynamic theories
The Mean square error (MSE ) is defined
MSE=
Where e is the individual tests deviation between calculated and measured temperature suppression and n is the number of samples tested
Table 5 shows the WHyP predictions of hydrate temperature suppression from measured activity The data are scattered and for the 51 samples in Table 5 the mean square error is 846degF To evaluate this deviation the measured activity of some chloride solutions were compared to tabulated activities showing a scatter in the activity measurements of up to 008 (mean square error of 047) Figure 9 shows a comparison between measured hydrate temperature suppression and suppression calculated by WHyP using measured and tabulated activity The MSE is 699degF for the calculations with measured activity and 217degF for temperature suppression calculated with tabulated activity Based on these results we conclude that the uncertainty in activity measurements causes most of the error when the method is used This method should be applied with care and not at all if there is uncertainty about the accuracy of the measured activity data
Test of Accurac Measurements
f J- 40 ~ c8 2 E 30 middot---shy
Ishy f c20shy~ g-
I---middot ---shy bullMeasured Activity
J Ul
bull bullbull A Tabulated Activity
o1__J~_J_~_L-==r==J
10 --shy --shy
0 10 20 30 40 50 Calculated Temperature Suppression
Novel Hydrate Prediction Methods for Drilling Fluids Page 20 Progress Report 122497
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Table5 dA Temperature suppress1on C Ia cu ate I dfram Measure ct1v1ty
measured calculated
Item Sample Water AT AT E Activity (F) (F) [F]
1 5 wt NaCl + 5 wt MeOH 09568 860 586 -274
2 10 wt NaCl+ 10 wt MeOH 08972 2100 1436 -664
4 5 wt NaCl + 5 wt Ethylene Glycol 09020 660 1365 705
5 1 o wt NaCl + 1 O wt Ethylene Glycol 09294 1680 970 -710
6 20 wt NaCl + 10 wt Ethylene Glycol 07962 3970 3005 -965
12 20 wt NaCl + 1 O wt Glycerol 08022 3570 2906 -664
13 20 wt NaCl + 20 wt Glycerol 07957 4210 3013 -1197
15 234 wt NaCl + 1 O wt Glycerol 06315 4030 6041 2011
16 221 wt NaCl + 15 wt Glycerol 06798 4350 5074 724
18 3 wt NaCl + 5 wt KCI + 5 wt Glycerol 09472 760 720 -040
19 5 wt NaCl + 5 wt KCI + 15 wto Glycerol 09213 1590 1086 -504
20 10 wt NaCl+ 10 wt KCI + 10 wt Glycerol 07443 2320 3888 1568
21 5 wt KCI + 5 wt Glycerol 09665 335 453 118
23 10 wt KCI + 10 wt Glycerol 09585 910 563 -347
24 5 wt CaCl2 + 5 wt Glycerol 09762 400 320 -080
26 10 wt CaCl2 + 10 wt Glycerol 09617 1010 518 -492
27 20 wt NaCl+ 20 wt GEO MEG 08126 3650 2737 -913
29 20 wt NaCl + 10 wt AquaCol-S 07771 3650 3323 -327
30 10 wt KCL + 10 wt AquaCol-S 08826 1160 1652 492
31 10 wt NaCl + 10 wt KCI + 10 wt AquaCol-S 08144 3050 2708 -342
32 20 wt Na-Formate + 10 wt AquaCol-S 08026 3020 2900 -120
33 20 wt NaCl+ 10 wt HF100N 07889 3640 3125 -515
34 15 wt KCI + 30wt HF100N 08271 2990 2505 -485
35 30 wt CaCl2 + 70 SynTec 07998 nh 2946 na
36 5wt NaCl 09149 375 1180 805
37 10 wt NaCl 08988 842 1414 572
38 125 wt NaCl 08859 1050 1603 553
39 20wt NaCl 08199 2823 2620 -203
40 2044 wt NaCl 08328 2700 2415 -285
41 26wt NaCl 07281 3520 4176 656
42 10 wt NaCl + 10 wt KCI 08344 2090 2390 300
45 20 wt KCI 08353 1700 2376 676
48 1442 wt Caci 09889 1400 149 -1251
49 15 wt Caci 09213 1520 1086 -434
50 1922 wt CaCI 09084 2190 1272 -918
53 10 wt0o Na-Formate 08462 617 2206 1589
57 20 wtoo Na-Formate 08107 1493 2768 1275
58 30 wt0o Na-Formate 07753 2993 3353 360
59 40 wt0o Na-Formate 08386 3920 2324 -1596
62 15 wt0o K-Formate 08599 873 1995 1122
66 30 wt0o K-Formate 07844 2395 3200 805
68 50 wt0o K-Formate 06697 nh 5270 na
69 21 wt0o Ca-Nitrate 08690 740 1856 1116
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Table 5 (continued)
Item Sample Water Activity
AT (F)
AT (F)
pound fFl
71 20 wt NaBr 08875 1672 1579 -093 72 30 wt NaBr 07829 2980 3225 245 74 10 wt CaBr2 08917 148 1517 1369 76 20 wt 0o Ca8r2 08435 998 2248 1250
77 30 wt CaBr2 08053 2324 2856 532 79 10 wt ZnBr2 09190 084 1119 1035 81 20 wt ZnBr2 08754 700 1759 1059 82 30wt ZnBr2 08435 1420 2247 827 97 30 wt Glycerol (167) 09423 1480 788 -692
100 10 wt AquaCol-S 09276 210 996 786
MSE 846
nh =No hydrate formation na = Not available
-Novel Hydrate Prediction Methods for Drilling Fluids Page 22 Progress Report 1224197
60
c 50 0middot ~ 40 a
sectshy~ 30ca a ~
I 20 a E $ 10
0
0 10 20 30 40 50 60
bull ~bullbull bull-
bullbull ~ bull bull bull bull ~v bullbull bull bull-
I bullbullmiddot- bull Calculated
temperature suppression
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Figure 10 Measured and Model Predicted Hydrate Temperature suppression LlT
using Mud Activity in WHyP
54 Prediction of the hydrate temperature suppression LlT using the inhibitor concentration ( wt)
This model can be applied with high accuracy to a wide range of inhibitor concentrations The 67 samples in table 6 give a mean square error of 175degF
Some caution should be used when applying the model to mud with high concentration of salts (close to saturation) as other components in the mud might effect the solubility limits
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Table 6 H d t dfrom mu d compos1 ion IV ra e temperature suooress1on ca Icu ate
Item Sample LiT LiTbull euro (oF) (oF) fdegFl
1 5 wt NaCl + 5 wt MeOH 860 770 -090
2 10 wt NaCl+ 10 wt MeOH 2100 1935 -165
4 5 wt NaCl + 5 wt Ethylene Glycol 660 654 -006
5 10 wt NaCl + 10 wt Ethylene Glycol 1680 1797 117
6 20 wt NaCl + 1owt Ethylene Glycol 3970 3916 -054
7 10 wt NaCl + 10 wt Propylene Glycol 1804 1615 -189
8 5 wt NaCl + 5 wtlo Glycerol 512 554 042
9 1Owt NaCl + 10 wt Glycerol 1268 1479 211
10 10 wt NaCl + 20 wt Glycerol 1950 2055 105
11 1Owt NaCl + 30 wt Glycerol 2661 2686 025
12 20 wt NaCl + 1Owt Glycerol 3570 3393 -177
13 20 wt NaCl + 20 wt Glycerol 4210 4419 209
14 20 wt NaCl + 20 wt Glycerol 4691 4419 -272
15 234 wt NaCl + 1Owt Glycerol 4030 4154 124
16 221 wt NaCl + 15 wt Glycerol 4350 4418 068
17 208 wt NaCl + 20 wt Glycerol 4590 4644 054
18 3 wt NaCl + 5 wt KCI + 5 wt Glycerol 760 736 -024
19 5 wt NaCl + 5 wt KCI + 15 wt Glycerol 1590 1460 -130
20 10 wt NaCl + 10 wt KCI + 10 wt Glycerol 2320 2836 516
21 5 wt KCI + 5 wt Glycerol 335 554 219
22 5 wt KCI + 10 wt Glycerol 566 577 011
23 10 wt KCI + 10 wt Glycerol 910 991 081
24 5 wt CaCl2 + 5 wt Glycerol 400 466 066
25 5 wt CaCl2 + 20 wt Glycerol 823 873 050
26 10 wt CaCl2 + 10 wt Glycerol 1010 1173 163
28 53 wt NaCl + 128 wt AquaCol-S 740 880 140
29 20 wt NaCl + 10 wt AquaCol-S 3650 3308 -342
30 10 wt KCL + 10 wt AquaCol-S 1160 954 -206
31 10 wt NaCl + 10 wt KCI + 1 Owt AquaCol-S 3050 2748 -302
32 20 wt Na-Formate+ 10 wt AquaCol-S 3020 3090 070
36 5wt NaCl 375 360 -015
37 10wt NaCl 842 924 082
38 125 wt NaCl 1050 1267 217
39 20 wt NaCl 2823 2468 -355
40 2044 wt NaCl 2700 2545 -155
41 26wt NaCl 3520 3555 035
42 10 wt NaCl+ 10 wt KCI 2090 1961 -129
43 5wt KCI 162 238 076
44 10wt KCI 692 587 -105
45 20wt KCI 1700 1485 -215
46 5 wt CaCI 234 296 062
47 5 wt0o CaCl2 234 296 062
48 1442 wt CaCI 1400 1412 012
49 15 wt CaCI 1520 1521 001
meas Calculated
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Table 6 (continued)
-
Sample iT (oF)
ilTbull (degF)
e [oF]
50 51
52 53
57 58
59 62
66 68 71
72 74 76
77 79
81 82
94 95
96 97
100
1922 wt CaCl2 2190 2289 099 21 wt CaC2 2300 2687 387 26 wt CaCl2 3900 4081 181 10 wt Na-Formate 617 536 -081
20 wt Na-Formate 1493 1632 139 30 wt Na-Formate 2993 3023 030 40 wt Na-Formate 3920 4187 267 15 wt K-Formate 873 757 -116 30 wt K-Formate 2395 2476 081 50 wt K-Formate nh 5232 na
20 wt NaBr 1672 1634 -038 30 wt NaBr 2980 2952 -028 10 wt CaBr2 148 355 207 20 wt CaBr2 998 1004 006 30 wt CaBr2 2324 2005 -319 10 wt0o ZnBr2 084 255 171 20 wt ZnBr2 700 714 014 30 wt0o ZnBr2 1420 1446 026 1owt Glycerol 700 260 -440 125 wt Glycerol 550 359 -191 20 wt Glycerol (110) 950 756 -194 30 wt Glycerol (167) 1480 1584 104 10 wt AquaCol-S 210 234 024
MSE 175
nh =No hydrate formation na = Not available
-
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Figure 11 Measured and Model Predicted Hydrate Temperature Suppression AT
using Mud Composition in WHyP
0 10 20 30 Calculated
temperature suppression
40 50
55 Prediction of the hydrate temperature suppression AT using the measured mud filtrate resistivity and density
This model was developed based on the observation of a correlation between the resistivity of ionic aqueous solutions and their effect on gas hydrate temperature suppression This correlation was developed in phase 1 of of this project and a detailed description is given in the report from phase 11
bull
The 37 samples in table 7 give a mean square error of 334degF
-
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Table 7 Hydrate temperature suppression calculated from mud filtrate
-
( 1) Density at 77degF measured 1n phase 1 (2) Density at 68degF tabulated CRC 48 edition (3) Measured resistivity (table 1) converted by temperature dependency to fit measured densiljL
res1st1v1ty and density measured calculated
Item Sample Temp [OF]
Resistivitx [ohm-m]31
Density [ppg]
tT [OF]
tT [OF]
f[oF]
4 5 wt NaCl + 5 wt Ethylene Glycol 600 01417 8698 660 533 -127 5 10 wt NaCl + 10 wt Ethylene Glycol 600 01203 9052 1680 1752 072
7 10 wt NaCl + 10 wt Propylene Glycol 770 01005 8983 1804 1332 -472
8 5 wt NaCl + 5 wt Glycerol 600 01390 8702 512 494 -018
9 10 wt NaCl+ 10 wt Glycerol 770 01083 9138 1268 1567 299
10 1O wt NaCl + 20 wt Glycerol 770 0 1209 9355 1950 2132 182
11 10 wt NaCl + 30 wt Glycerol 770 01559 9592 2661 2795 134
12 20 wt NaCl + 1 O wt Glycerol 600 00524 9774 3570 2892 -678
13 20 wt NaCl + 20 wt Glycerol 600 00709 10072 4210 4254 044
14 20 wt NaCl + 20 wt Glycerol 600 00927 10072 4691 4447 -244
15 234 wt NaCl + 1 Owt Glycerol 600 00799 10112 4030 4509 479 16 221 wt NaCl+ 15 wt Glycerol 600 00685 10144 4350 4460 110 18 3 wt NaCl + 5 wt KCI + 5 wt Glycerol 600 01354 8901 760 921 161 19 5 wt NaCl + 5 wt KCI + 15 wt Glycerol 600 0 1386 9251 1590 1774 184 20 10 wt NaCl + 10 wt KCI + 10 wt Glycerol 600 00525 9708 2320 2691 371
21 5 wt KCI + 5 wt Glycerol 600 01174 8721 335 479 144
22 5 wt KCI + 10 wt Glycerol 770 01505 8795 566 777 211
23 10 wt KCI + 1 O wt Glycerol 600 01223 9095 910 1375 465
24 5 wt CaCb + 5 wt Glycerol 600 01586 8787 400 684 284
25 5 wt CaCl2 + 20 wt Glycerol 770 02151 9035 823 1316 493
26 10 wt CaCl2 + 1 O wt Glycerol 600 01386 9243 1010 1753 743
28 53 wt NaCl+ 128 wt AquaCol-S 770 01932 8805 740 928 188
29 20 wt NaCl + 10 wt AquaCol-S 600 00883 9680 3650 2911 -739
30 10 wt KCL + 10 wt AquaCol-S 600 00825 9096 1160 1300 140
31 10 wt NaCl + 10 wt KCI + 10 wt AquaCol-S 600 00556 9680 3050 2718 -332
36 5 wt NaCl 770 01283 8617 375 408 033
37 10 wt NaCl 770 00649 8918 842 857 0 15
38 125 wt NaCl 600 00734 9105 1050 1267 217
39 20wt NaCl 600 00530 9584 2823 23 18 -505
40 2044 wt NaCl 600 00512 9585 2700 2251 -449
42 10 wt NaCl + 10 wt KCI 600 00512 9513 2090 2024 -066
43 5wt KCI 770 01316 8588 162 355 193
44 10 wt KCI 770 00672 8862 692 720 028
45 20 wt KCI 680 00472 9453 1700 19 11 211
47 5 wt0o CaCl21 1 770 01449 8680 234 541 307
49 15 wt0o CaCl21 680 00689 9150 1520 1467 -053
50 1922 wt CaCl2 680 00509 9345 2190 1702 -488
MSE 334 1
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0--~----~L-~~~--~~------~~----~~~-
0 10 20 30 Calculated
temperature suppression
40 50
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Figure 12 Measured and Model Predicted Hydrate Temperature Suppression ~T
using Mud Filtrate Resistivity and Density in WHyP
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6 References
1 Novel hydrate prediction methods for drilling fluids Westport report no WTClshy96-133 June 24 1996
2 van der Waals JH and PlatteeuwJC Adv Chem Phys 2 1-55 (1959)
3 KatzDLPrediction of Conditions for Hydrate Formation in Natural Gases Petroleum Technology AIME Technical Publication No 1748 (July 1944) 140-149
4 Yousif MH Young DB A simple correlation to predict the hydrate point suppression in drilling fluids SPEIADC paper 25705 1993
5 McLeod HO Campbell JM JPT 13 590 1961
6 Thakore JL Holder GD 1987
7 de Roo JL et al 1983
8 Verma VK 1974
9 Jhaveri J Robinson DB 1965
10 Wilcox WI Carson DB Katz DL 1941
11 Holder GD Hand JH 1982
12 Ng H-J Robinson DB 1985
13 Avalonitis DA 1988
14 Ebeltoft H Yousif M and Soergaard E Hydrate control during deep water drilling Overview and new drilling fluid formulations SPE 38567 1997 SPE Annual Technical Conference and Exhibition San Antonio Texas Oct 1997
Novel Hydrate Prediction Methods for Drilling Fluids Page 29 Progress Report 1212497
((( ) ) wt) wtL n-l a+l -- +--Mws Mwg
x =(wt) wt wtwL ~- +--+---3
Mws Mwg Mww mix
wt 3mix = b1 wt wwt g Mw Jwt wt g [ -b2 Mw Mw
Table A1 Th e SaIt P ropert1es m WHIVIP
Mw Degree of ionization a Concentration limit
(gmole) ( c =wt I Mw) (wt) ( c) NaCl 58440 01 (40033554 + (659587579 + (21604556 + 264 0452
(3383139 + 01959452 ln(c)) ln(c)) ln(c)) ln(c)) KCI 74555 0730430 - (309047 - (1601070 - 471227 c) c) bullc 255 0320 CaCl2 110986 0754608 - (240036 + (474824 + 206364 c) bullc) bullc 300 0270 NaBr 102894 1379254 - (493934 - (1986963 - 389332 cl c) bullc 475 0462 CaBr2 199888 0938196 - (1594105 - 0890007 c) bullc 320 0160 ZnBr2 261238 0938196 - (1594105 - 0890007 c) bullc 320 0122 NaCOOH 68008 0237573 + (0317955 - 237197 bullc c) middotc 420 0618 KC OOH 84120 0237573 + (0317955 - 237197 bullc c) bullc 500 0594 Modifications
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APPENDIX A
The data used by WHyP for calculation of temperature suppression from mud composition
The inhibitor components specific properties were collected from the literature when available some slightly modified for better representation of hydrate temperature suppression The method of calculating gas hydrate temperature suppression from inhibitor concentration uses the ionized fraction of salt rather than the total fraction
The general expression for inhibitor fraction is
Where wt 5 wt9 and wtw are salt glycol and water weight percent (g I 100g) respectively M M9 and Mw are salt glycol and water molecular weight ~ is the interaction coefficient between salt and glycol
The interaction coefficient ~ is calculated by
J
When either fraction of salt or glycol goes to zero ~ disappears and the inhibitor fraction is reduced to Hammerschmidts original equation The empirical constants b1 and b2
fitted from experimental data
The degree of ionization (a) for salt in water is available in the literature Table A1 contains the polynomial fit for degree of ionization used by WHyP
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Calcium chloride (CaCl2) degree of ionization The tabulated degree of ionization was found to respond better over the entire concentration range when the inhibitor fraction was given the form
Bromide and Formate degree of ionization The degree of ionization was not found tabulated for CaBr ZnBr2 NaCOOH and KCOOH Instead a fictive value was fitted from the experimental data of gas hydrate temperature suppression
Table A2 The GI 1esm IY1ycoIProperf WHP
Mw Concentration limit (gmole) (wt) ( c) 32042 0579Methanol 400 62029Ethvlene Glvcol 400 0645
Proovlene Glycol 76090 400 0526 92095 400 0434Glvcerol
100middot 0400Polyallcvlene Glycol 400 - ( 1) Using modified molecular weight
Modifications Methanol (MeOH) molecular weight The model predicts too high inhibiting effect of methanol when using the true molecular weight (Mw = 32042 gmole) A better response is observed when the molecular weight is corrected by
In(wt)Mw~eOH = MwMeOH
07923
Polyalkylene Glycol molecular weight The model predicts too low inhibiting effect of polyalkylene glycol when using the true molecular weight (Mw = 600 gmole) A better response is observed when a fictitious molecular weight of 100 gmole is used
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