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ICPTT 2011 © 2011 ASCE
179
Applicable Material Selection for Oil Country Tubular Goods (OCTG) in Sour
Conditions and Software Development
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Bing Shao1, Xiangzhen Yan2, Xiujuan Yang3 Tongtao Wang4 and Gensheng Li5
1 Doctor, College of Mechanical and Electronic Engineering, China University of
Petroleum; No.739, Beiyi Road, Dongying 257061; Email: sealkite@163.com; Tel:
PH (86) 0546-8391820
2 Professor, College of Pipeline and Civil Engineering, China University of
Petroleum; No.739, Beiyi Road, Dongying 257061; Email: yanxzh@163.com; Tel:
PH (86) 546-8392356
3 Professor, College of Pipeline and Civil Engineering, China University of
Petroleum; No.739, Beiyi Road, Dongying 257061; Email: yangxj999@163.com;
Tel: PH (86) 0546-8392356
4 Doctor, College of Mechanical and Electronic Engineering, China University of
Petroleum; No.739, Beiyi Road, Dongying 257061; Email: hdupcwtt@163.com; Tel:
PH (86) 0546-8391820
5 Professor, State Key Laboratory of Petroleum Resource and Prospecting, China
University of Petroleum, Beijing, 102249, China; Email: ligs@cup.edu.cn; Tel: PH
(86) 10-89733379
ABSTRACT
Through analyzing different guidelines and standards for material selection of OCTG
in sour conditions, belonging to six companies in four countries, we generalized the
main factors that influence the material selection of OCTG. Based on integrating and
optimizing these six guidelines on the materials’ safety and corrosion resistance
properties, a synthetic method for selecting materials has been brought forward. And
further, software for material selection of OCTG in sour conditions has been
developed. This software can provide results of six widely used materials selection
guidelines of Sumitomo, NKK, Kawasaki, Lonestar, DMV and Cabval, and
meanwhile, the best solution can be provided by the synthetic module. The East
Sichuan region has been taken for example. Input the environmental parameters and
then the results of different guidelines and suggested one are obtained. By comparing
them with recommended and adopted materials for well completion, it demonstrates
that the results provided by the software are accurate and reliable.
KEYWORDS
Sour Conditions; OCTG; Material Selection; Software
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INTRODUCTION
For a long time, corrosive gases in oil and gas fields like CO2 and H2S have done
much damage to tubing and casing strings and have reduced their security and
reliability a lot. Strings with traditional steels can’t be competent for production
environment with high temperature and high CO2/H2S concentration. The scientific
and suitable selection of the materials of casing strings could effectively prevent and
decrease the destructions on strings caused by the corrosion of CO2 or H2S. However,
far less research has been done for the corrosion when CO2 and H2S coexist than that
CO2 or H2S solely exists (Jiao et al, 2003 and Ma et al, 2006) and the guidelines for
selection of CRA mainly are regulations or references used within oil companies and
enterprises (NACE Standard MR0175, 1999 and Stress Engineering Service Inc,
2001). They are scattered and short of systematicness. For this, based on the analysis
of different guidelines and standards for materials selection of casing in gas well
containing CO2 and H2S, the CAE Technical Lab in China University of Petroleum
has developed a synthetic guideline which can provide more suitable materials.
Meanwhile, a software system that can provide applicable materials according to
different guidelines and standards with given environmental parameters is developed.
And through synthetic comparison and analysis among different applicable materials,
suggested result will be offered. This software is easy to operate and the result is
accurate and reliable, which could improve the efficiency of selecting materials
under acid conditions markedly.
DIFFERENT OCTG SELECTION CRITERIONS
Currently there are six guidelines for material selection of casing in gas well
containing CO2 and H2S which are world widely used. Here we give a brief
introduction to these guidelines and the synthetic guideline which is developed from
research on these six guidelines.
Synthetic Guideline. Nowadays, there are a small number of computing models for
steel’s corrosion rate in case of CO2 and H2S coexisting. Based on the models of De
Waard and Mishra for sole existence of CO2 or H2S and the data got from the
autoclave simulative experiments (De Waard C et al, 1991; Mishra et al, 1997; Li et
al, 2004;), we can establish a computing model for corrosion rate in case that CO2
and H2S coexist:
ln rcorr = A −
(
⎡
⎛
Q
B
Q'
+
− C ⋅ pH + D ⋅ ⎢1 − exp ⎜ −
⎜ PH S
KT
T
⎢⎣
2
⎝
E ⋅ ln PH 2 S
)
2
+ F ⋅ ln PH 2 S + G ⋅ ln PCO 2 ,
ICPTT 2011
⎞⎤
⎟ ⎥ ln PCO +
2
⎟⎥
⎠⎦
(1)
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181
Where, A, B ,...G are constants and coefficients decided by the experimental data and
have considered the influence of solution flow rate and ions such as Cl − 、Mg 2+ 、Ca 2 + ,
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Q
is activation energy,
Q'
is activation energy for formation of FeS film, K is
universal gas constant.
The corrosion rate of steels in conditions where CO2 and H2S coexist is related to
factors like partial pressures of CO2 and H2S, temperature, pH, concentration of Cl −
(NORSOK Standard M-506, 2005) and so on, which can be shown in the formula
given above. The guidelines for selection of materials widely used today are also
based on these conditional parameters.
In synthetic guideline, through the analysis and comparison among the results of
other six guidelines with same parameters, which is also the comparison among the
sulfide stress corrosion cracking (SSCC) resistance properties of different types of
steel, the conservative materials will be chosen as the suggested result. The SSCC
resistance properties of different types of steels are shown in table 1.
Table 1. The SSCC Resistance Properties of Different Types of Steels
Stainless
Steel Martensitic Ferritic
Austenitic Duplex(ferrite/austenite)
type
Ordinary
preferable excellent excellent excellent
corrosion
resistance
SSC resistance
bad
bad
excellent preferable
SCC resistance
excellent
excellent bad
preferable
The required parameters in synthetic guideline have considered all parameters in
other modules, including partial pressures of CO2 and H2S, temperature, pH,
concentration of Cl − . Analyze the dividing values of parameters in each guideline
and re-divide the selecting regions containing different applicable materials each.
Based on analysis of safety and corrosion resistance properties of different materials
in same selecting region, the most appropriate materials in this selecting region can
be got.
Sumitomo Guideline. In this guideline, materials will be selected according to the
partial pressures of CO2 and H2S. Temperature and the concentration of Cl − conduct
as the constraint conditions like that the service temperature of SM 13CRS-80 should
no be higher than 175℃ and SM 9CR should be used in case that the concentration
of Cl − is less than 50000ppm.
Additionally, the valid parameter ranges of Sumitomo guideline are much extensive.
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The valid ranges of CO2 and H2S partial pressures both reach 100MPa and the
limitative temperature reaches 300℃. In addition, in order to prevent the corrosion of
CO2 and H2S, Sumitomo Company has developed New SM-Series steels that
behavior pretty well in high temperature, high CO2/H2S pressure and high Cl −
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concentration environment, which is also one of the reasons for Sumitomo
guideline’s extensive application.
NKK Guideline. In NKK guideline, materials will be selected according to the
partial pressures of CO2 and H2S, temperature and the concentration of Cl − ,
excluding the effect of pH. Temperature and the concentration of Cl − will be
necessary only in specific CO2/H2S pressure ranges, and in this case, materials will
be selected based on temperature and the concentration of Cl − only.
Kawasaki Guideline. In Kawasaki guideline, materials will be selected according to
the partial pressures of CO2 and H2S, temperature and pH, excluding the effect of the
concentration of Cl − . Temperature and pH are secondary parameters that will be
necessary only in specific CO2/H2S pressure ranges.
Lonestar Guideline. In Lonestar guideline, materials will be selected only based on
the partial pressures of CO2 and H2S and the effects of other factors have not been
considered.
Lonestar guideline is similar to Sumitomo guideline in dividing values of partial
pressures of CO2 and H2S, but there is no limit in temperature, pH or other conditions
for materials selected in Lonestar guideline.
DMV Guideline. Decision conditions for selecting materials are given in this
guideline and firstly, users make the judgment whether the concentrations of certain
corrosive medias are: PCO2 concentration >10.3MPa; Cl − concentration >250 g/L;
PH2S concentration > 6.89×104Pa; T > 99℃. If any of the concentrations in
production fluid exceeds any of the critical conditions shown above, then the
necessary parameters would be necessary and based on the pressure of H2S and
temperature, applicable CRA would be picked out.
DMV guideline only provides CRA selection suggestions in certain conditions and
the effects of pressures of CO2 and H2S, temperature and the concentration of Cl −
have been considered, except that of pH.
Cabval Guideline. Cabval guideline is similar to DMV module in decision
conditions, but it has a more extensive applicable scope. The temperature and H2S
pressure will be necessary when any of the concentrations in production fluid
exceeds any of the critical conditions.
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SOFTWARE DEVELOPMENT
Fig. 1 shows the block diagram of the software which is designed in modular structure
and the modules keep mutually independent as much as possible to make it easy for
operation, modification and function extendedness. The software is composed by
seven modules which are Synthetic module, Sumitomo module, NKK module,
Kawasaki module, LoneStar module, DMV module and Cabval module. Different
applicable solutions and the suggested one can be offered at the same time. The
results could be outputted in text which can be further edited and saved. Fig. 2 shows
the main operation interface in synthetic module.
Figure 1. Block diagram of the software
ICPTT 2011
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ICPTT 2011 © 2011 ASCE
184
Figure 2. Operation interface of synthetic module
EXAMPLE ANALYSIS
The East Sichuan region is the main working district for Sinopec South Branch for
Exploration & Development. The working environment there is pretty extreme and
the depth of well is within 6500m, temperature is within 150℃, formation pressure is
within 65MPa, natural gas partial pressure is within 15MPa, CO2 partial pressure is
within 15MPa and the concentration of Cl − is within 15000ppm. The recommended
materials
for
well
completion
were:
SM2535/SM2242
for
T:132℃~149℃&PH2S<1.4MPa or T<132℃ when there is no free
sulfur;SM2535/SM2242 for T<132℃, SM2550 for T: 132℃~149℃ where free
sulfur exists.
Environmental Parameters. According to the known conditions, we can take the
environmental parameters shown in Table 2 where the unknown pH is adopted as the
neutral value pH=7.
Table 2. Environment Parameters
CO2
partial H2S
partial Temperature Cl − concentration
pressure
pressure
15MPa
1.4MPa
150℃
15000ppm
pH
7
Materials selected by the software. Input the environmental parameters and we can
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ICPTT 2011 © 2011 ASCE
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get the results of different modules shown in Table 3.
Table 3. Materials Selected by Different Guidelines
Different Materials selected
Guideline
s
Synthetic SM 2535-110,125,130(25Cr-35Ni-3Mo);
Module
SM 2035-110,125(20Cr-35Ni-4Mo);SM 2242-110,
125(22Cr-42Ni-3Mo)(≤250℃);DMV 928(Alloy 28 28Cr-32Ni)
(Note) SM 2050, SM 2060, SM C276 (18Cr-54Ni-16Mo-W) are
available for well containing free S.
Sumitomo SM 2535-110,125,130;SM 2035 - 110, 125;
Module
SM 2242 - 110, 125 (≤250℃)
(Note) SM 2050, SM 2060, SM C276 (18Cr-54Ni-16Mo-W) are
available for well containing free S.
NKK
High Nickel Alloy NK NIC series,
Module
SANICRO 28(27%Cr-31%Ni-3.5%Mo),
INCONEL 825(22Cr-42Ni-3Mo)
Kawasaki OFF EVALUATION
Module
Lonestar
SM-2035(20Cr-35Ni-4Mo),2535(25Cr-35Ni-3Mo),2242(22Cr-42Ni-3M
Module
o)
DMV
Material type:Austenitic Alloy: DMV 928(27Cr-32Ni-3.5Mo)
Module
DMV C-276(C-276;C -276) are available for well containing free S.
Cabval
ALLOY 825(Ni-Fe-Cr Alloy: 42Ni-22Cr-3Mo)
Module
Based on the environmental parameters shown in Table 2, materials can be selected
by the software as shown in Table 3. Materials selected by Synthetic module are
suggested result through comparison among results from other six modules on safety
and corrosion resistance properties.
Result Discussion. The materials in Table 3 are all high-alloy steels and we can
discuss them from two cases that whether free S exists or not.
In the case with no free S, ALLOY 825 has the same components to SM2242.
Materials selected by Lonestar module are same to that by Sumitomo module. The
component contents of SANICRO 28 is similar to that of DMV 928, but the former
has one percent of nickel less, so conservative alloy DMV 928 should be kept. In the
other case with free S, the suggested materials DMV C-276 and SMC276 have
identical components.
Through the analysis and comparison above, we can get the suggested materials:
ICPTT 2011
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ICPTT 2011 © 2011 ASCE
186
SM2535, SM2035, SM2242 (ALLOY 825) or DMV 928 without free S; SM2050,
SM2060 or SM C276 with free S, which are corresponding to materials selected by
Synthetic module.
Generally the higher the alloy content is, the better the performance will be, but with
a higher cost. So the final material selection should combine the best performance
with the lowest cost. The materials provided by the software are based on safety and
corrosion resistance properties and the cost has not been included. In this example,
we also can reach a best solution with best performance and lowest cost: SM 2535
for no free S and SM2050 for free S.
Return to the recommended materials for well completion, it is appropriate to adopt
SM2535 or SM2242 for no free S existing, but when free S exists and temperature is
less than 132℃, neither SM2535 nor SM2242, but SM2050 is the proper material. In
this area, SM2242 has been adopted as casing material for PuGuang well 304-3,
which is proper.
CONCLUSION
Applicable materials optimization software for OCTG in sour conditions makes it
convenient to select proper materials for specified conditions. It can provide users
with multi-choice suggestions on the basis of safety and steels’ corrosion resistance
properties and by combining them with the economic conditions or other
requirements, users could make the final decision. This software system is easy to
operate, the result recommended by it is accurate and reliable and it could further
enhance the product efficiency.
ACKNOWLEDGMENT
The authors are very much indebted to Important National Science & Technology
Specific Projects (Contract No. 2008ZX05036) and the People’s Republic of China
“973 Projection” (Contract No. 2010CB226706) for the financial supports.
REFERENCES
De Waard C, Lotz U, Milliams D E. (1991). Predictive model for CO2 corrosion
engineering in wet natural gas pipelines. J. Corrosion, Dec, 976-985.
Jiao, W.D., Zhang, Y.Z. and Zhang, Q. (2003). Corrosion law of CO2 and H2S on oil
country tubular goods. J. Chemical Engineering & Machinery, Apr, 250-253.
Joint Industry Project Report. (2001). Best practices for prevention and management
of sustained casing pressure, Houston, Stress Engineering Service Inc.
Li, Q.A., Bai, Z.Q., Huang, D.Z., et al. (2004). Predictive model for corrosion rate of
ICPTT 2011
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ICPTT 2011 © 2011 ASCE
187
oil tubes in CO2/H2S coexistent environment PartⅠ:building of model J.
Journal of Southwest Jiaotong University, Feb, 141-147.
Ma, L.P., Wang, Y.Q. and Zhao, S.H.(2006). Coexistence of CO2 and H2S corroding
tubing under down hole environment. J. West-China Exploration Engineering,
Nov, 50-52.
Mishra B, Hassan S A, Olson D L, et al. (1997). Development of a predictive model
for activation-controlled corrosion of steel in solutions containing carbon
dioxide. J. Corrosion, Nov, 852-859.
NACE Standard MR0175: Sulphide stress cracking resistance metallic materials for
oilfield equipment. (2001). NACE, Jan.
NORSOK Standard M-506: CO2 corrosion rate calculation model. (2005). NORSOK,
Mar.
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