Material Selection Considerations for CO2 Sequestration Projects
Table 3: Information Required for Materials Selection for Internal Environments
System Essential Information for Material Selection
Equipment Type of fluid
carrying Presence of free water produced Mol % CO2
fluids ppm H2S pH (estimation of )
Operating temperature Design pressure
Bubble point pressure Design temperature
Min. blowdown temperature Presence of O2 or free S
(free S can be in the gas or condensate) Sand content
Project life (years) Ambient temperature
Presence of mercury Water dewpoint in gas systems Water content of the gas Inhibition philosophy Flow rates
SLC = service life corrosion.
Table 4: Information Required for Materials Selection for External Environments
Equipment Information Required Wells
Pipelines
Nature of annulus fluid* Presence of shallow-water aquifers and cement intervals**
Buried or above ground Corrosive environment (fresh water, brackish water, seawater, soil type, etc.) External surface temperature Onshore or offshore Insulated or standard coatings Pipe in pipe Soil resistivity
Facilities
Normal atmospheric conditions (on land) or salt spray (offshore/coastal area) Ambient temperature Presence of external lagging Water, free or condensed
*External environments for tubulars, where annulus fluids are pH-controlled closed systems and where biocides are sometimes added to control bacteria, are not normally a problem for carbon steels. The potential impact of different annulus fluids on corrision-resitant alloy materials should be considered. **If the external casing is in contact with more than one aquifer, the electrochemical potential of the casing can be different in each aquifer, which can result in severe corrosion.
required for material selection is shown in the second column and the additional information required for SLC calculations (for carbon steel) is shown in the third column.
External Environments
The external environment might affect the selection of materials or the method chosen to provide protection from external corrosion (see Table 4).
Selection of Suitable Materials Basic Assumptions
The environmental limits for production fluids in terms of CO2, H2S, temperature, chloride content, pH, etc., represent basic recommendations about the suitability of the material for such an
environment. In some cases the actual limits of applicability of individual materials might be higher than those shown in the tables.
66 Additional Information
Required for SLC Calculation The full stream molar composition
Whether inhibitors are to be injected
Details of flow regime
Chloride level (of produced water) Flow velocities of all phases Operating pressure
Water content in glycol
(where added for corrosion or hydrate control)
HCO3- content of water, or preferably, full water
composition
Concentration of organic acids Projected operating pressure and temperature profile over life of project
Heat transfer coefficients of coating systems used (pipelines)
<3
Water contact with walls
Water contact with walls
<3
Water contact with walls
(corrosive or sour service)
Table 5: Downhole Tubing, Liners and Casing Production
Conditions
SLC Temp. Sour NaCl domain* or pH2S
(mm) (°C) <3
<3 (mbar) (g/l)
<200 Domains Any CS, ISO 11960, 0 or 1
any strength grade
<200 Domains Any CS, ISO 11960 Q+T 2 or 3
grades with hardness ≤250HV (? 22HRC) and C90/T95 grades**
80–200 Domains Any CS, ISO 11960 2 or 3
Grade P110 or lower strength**
110–200 Domains Any CS, ISO 11960, 2 or 3
N/A <110 <3.5 <165 13Cr N/A <170 <3.5 <20 13Cr
(corrosive sweet N/A <140 <3.5 <165 S13Cr service)
N/A <200 <3.5 <20 S13Cr N/A As non- <5 sour
(corrosive, slightly N/A sour service)
<100
As non- 13Cr or S13Cr† sour
(pH >3.5)
13Cr or S13Cr† (pH >4.5)
Wet/condensate N/A <100 Any Any GRE lined CS N/A <100 Any Any GRE‡
CS = Carbon Steel; GRE = Glass Reinforced Epoxy; HRC = Rockwell Hardness; SLC = service life corrosion. *Sour domains are defined in ISO 15156 Part 1.
**Where necessary, higher-strength grades might be qualified for a specific application. Guidance on qualification testing can be found in ISO 15156 Part 1. †Limited to L80 13Cr (AISI 420). Compared to 13Cr, super 13Cr grades have higher strength (P110) and improved resistance to pitting in sweet conditions, but no improved cracking resistance in sour conditions. The temperature and chloride limits are as defined for
conditions with <3.5mbar H2S. In specific applications specific super 13Cr alloys can be shown to give better performance than 13Cr. In general, however, there is no guarantee that one super 13Cr alloy will perform better than the average 13Cr. If there is an incentive to use super 13Cr then laboratory qualification testing is required. ‡
With GRE there are limitations on the combination of pressure and diameter – for increasing diameter the pressure rating decreases.
Grade Q-125 or lower strength.
Material
The limits quoted are based on the assumption that the pH of the environment is 3.5, unless otherwise stated. A pH of 3.5 is selected because this is the most severe condition for production operations (e.g. gas systems with only condensed water). Lower-pH environments can occur for short periods of time during acidising and flow-back of (partially) spent acids. If not properly controlled, these conditions can lead to severe corrosion.
If the pH is expected to be higher (less acidic), some relaxation of these limits might be possible. Where required, materials can be qualified for service outside the conditions indicated in the following sections by consulting a materials specialist and, where necessary, undertaking
laboratory testing. In the tables, <3.5 mbar (0.05psi) pH2S designates a non-sour environment with respect to the NACE MR 0175 classification; this is the ‘domain 0’ in ISO 15156.
Production Systems Downhole Tubing and Liners
Detailed production tubing material selection depends upon an analysis of the flow regime, corrosivity of the well fluids, materials properties and economic factors. Table 5 gives general guidelines on suitable materials depending on the cumulative corrosion loss anticipated for the lifetime of the well and the anticipated environmental conditions. Here SLC is used as one of the factors in materials selection. This is a common approach used in all these
EXPLORATION & PRODUCTION – VOLUME 9 ISSUE 2
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